CA2520807A1 - Enhancing silver tarnish-resistance - Google Patents

Abstract

An alkanethiol, alkyl thioglycollate, dialkyl sulfide or dialkyl disulfide may be used to surface treat of an alloy of silver containing an amount of germanium that is effective to reduce firestain and/or tarnishing. The treatment has been found to further reduce tarnishing of the alloy such that a sample can be supported close above a 20% solution of ammonium polysulphide for at least 30 minutes while retaining a generally untarnished appearance.
The treatment may be carried out at the end of manufacturing a shaped article to give rise to an article that will preserve its untarnished appearance both during transit to a point of sale but during subsequent display for an extended period. The invention therefore also includes a method for manufacturing a tarnish-resistant silver article, which comprises the steps of forming a shaped article of an alloy of silver containing an amount of germanium that is effective to reduce firestain and/or tarnishing, surface treating the article with an alkanethiol, alkyl thioglycollate, dialkyl sulphide or dialkyl disulphide; and introducing the article into packaging.
Also disclosed for use in treating an alloy of silver as aforesaid is a water-based composition comprising a treatment agent selected from an alkanethiol, alkyl thioglycollate, dialkyl sulfide or dialkyl disulfide and a mixture of an anionic surfactant and an amphoteric or nonionic surfactant in a concentration that is effective to solubilise the treatment agent.

Description

_ 1 -1CNIIANCING SIL'V'ER TAIINISII-RESIaTANCE
FIELV OF THE IhIVENTIQN
s The present invention relates to the use of organo-sulphur compounds in the enhancement of the tarnish resistance of silver alloys, to silvez articles of enhanced tarnish resistarxce that have been surface-treated with the organo-sulphar compounds and to methods of keeping and display of the treated articles.
It also relates to a water-based composition that can be u$ed far the treatment of a to metal which may be a silver allay but which may also be another metal requiring surface treatment to impart tarnish resistance e. r. copper, brass or nickel.
BAt=.'K~ROUND TO THE INVENTIf)N
13 Silver alloys and their tarnish-resistance Standaxd Sterling silver proviaea manufacturers and silversmiths with a versatile and reliable material but it is inevitable fat finished articles will require further clemin'e, and polishing to temporarily remove undesired tarnish products.
z0 It is yvell-known that yvith exposure to everyday atmospheric conditions, silver and silver alloys develop a lustre-destroying dark film known as tarnish.
Since znoient times it has been appreciated that unalloyed 'one' silver is too soft to 'withstand normal usage, sad it has been the practice to add a 25 proporiivn of a. base metal to izicrease hardness rrnd strength. In the U'K, IegislatiQn that bas existed since the fourteenth century specifies a minimum silver content of articles for sale at 92.5% {the Sterling standard), but does not specify the Ease metal GOFISLItlli:ntS, Experience 4onvinced early silversn3iths That copper was the most suitable of the rrtetals available to them. Ivlodern silver sheet 3o manufacturers generally adhcr~; to this composition, although sc~metirnes s, proportion of copper is replaced by cadmium to attain even greater ductility.

z .-Sterling ,,vith a 2.5% cadrniurn content is a standard material for sp~ii~g and stamping. Lower grades of silv':r alloys are eorr~xnorz in many parts of Europe for the production of hollow-ware and cutlery. The 800-grade alloys (Ag parts per thousand) arc predominantly used in southern and mid-Europe whereas .in Scandinavia the 830 standard is predominant.
In all btrt the largest manufacturing companies, most of the annealing and sbldering required to assemble finished or semi-finished articles is carried out with the flame of an air-gas blowtorch. The oxidising or reducizlg nature of the flame and the temperature of the articles are controlled only by the drill of the silversmith. Pure silver allows oxygen to pass easily through it, particularly when the silver is heated to above red heat, Silver does not oxidise in uir, but the copper in a silver/copper alloy is oxidised to cuprous or cupric oxide. Pickling of the oxidised surface of tl~e article in ltot dilute sulphuric acid removes the superficial but not the deeper-seated copper oxide so that the surface consists of fine or unalloyed silver covering a layer of silverlcopper oxide mixture. The pure silver is easily permeated fluxing further heating, allowing copper located deeper below the surface to beco~.e oxidised, Successive annealing, cold working and pickling produces a surface thatwexhibits the pure lustre of silver when lightly polished but z0 . with heavier polishing reveals dark and disfiguring stains known as 'firestain' or 'fire'. Soldering operations are much more produc,~tive of deep firestain because of the higher tenrrperaturas involved. Wlaen the depth of the firestain exceeds about 0.025mm (0.010 inches) the alloy is additionally prone to cracking Fmd diflicuZt to solder because an oxide surface is not wetted by solder so that a proper ZS nlstallurgical'band is not formed.
Patent GB-B-2255348 (R,ateau; Albert and Johns; Metaleurop Recherche) disclosed a novel silver allay that maizitaimed the properties of hardness and lustre inherent in Ag-Cu alloys while reducing problems resultW Q from the tendency of 3~ the copper content to oxidise. The alloys were ternary Ag-Cu-Ge alloys containing at least 92.5 w-t°l° Ag, O.S-3 wt% Go and the bal<~nce, apart from 3 _ inzpuritics, copper. The alloys were stated to be stainless in ambient air riuri~~g conventional production, transforzr,ation and f nishing operations, to be easily deformable when cold, to be easily brazed end not to give rise to significant shrinkage on casting. They were also stated to extzibit superior ductility acrd S tensile strength and to be annealable to a required hardnLss. Germanium was stated to exert a protective function that toes responsible for the advantageous combination of properties exhibited by the new alloys, and was in solid solution in both the silver and the Copper phases. The microstructure of the alloy was said to be constituted by two phases, a solid solution of germanium and copper in to silver surrounded by a filamentous solid solution. of gennauium anal silver and coppex. 1~e germanium in the copper-rich phase was said to inhibit .surface oxidation of that phase by forming a thin Ge0 or Ge4z protective coating which prevented the appearance of fire5tain dtu trig brazing and flame annealing wlzioh results from the oxidation of copper at high temperatures. Furthermore the 15 development of tarnish was appreaiubly delayed by the addition of germanium, the surface turned sliglxtly yellow xather than black and tarnish products wore costly reazoved by ordinary tap water, The alloy was said to be useful inter crlia in ja~vellery. However, the alloy disclosed in the above patent Suffers limitations insofar as it cm exlubit large grain size, leading to poor deformatGOn properties 20 and formation of large pools from low-melting eutectics resulting in~localiscd surface melting when the alloy is subject to the heat of an air torah, Patents CTS-~-6168071 and ~P-B-0729398 (Johns) disclose a silverlgennanium alloy which carnpxiscd a silver contEnt of at Isast 77 wt %
and a 25 germaniu;n content of between 0.4 and 7%, the remainder princfpally being copper apart froze any impurities, which alloy contains elemental boron as a Srain refiner at a concentration of more than (?ppm and less than 20ppm. The boron content of the alloy can be aehievzd by providing the boron in a master eapperlboron alloy having 2 v4~t % elemental boron. Zt was roported that such low 30 conGontrations of boron surprisingly provide excellent grain refining in a silverlgerrrzaniunz alloy, impa~rking e~reater strength and ductility to the alloy c~
compared with a silverlgermaniuxn. alloy without boron. The boron in the alloy inhibits grain growth even at temperatures used in the jewellery trade for soldering, and samples of the alloy were reported to have xesisted pitting even upon heating repeatedt~r to temperatures where in conventional alloys the copperlgezmanium eutectic in the alloy would melt, Strong and aesthetically pleasing joints between separate elements of the alloy oar be obtained without using a filler material between the free surfaces of the two elements and a butt or lap joust can be formed by a diffusion process or resistance or laser welding techniques. Compared to a weld in Sterling silver, a weld in the above-described to alloy has a much smaller average grain size that irzzproved the formabiliL3~ and ductility of the welds, and an S3q alloy has bccn wcldcd by plasma welding and polished without the need for grinding.
Ternary and quaternary allays e.g. Ag-Cu-Ge alloys and A,g-Cu-Zn-Ge alloys include two base metal. ahoying elements, Gu and Ge, in a noble parent metal, Ag. Grx exposure to an oxidising at~.osplaere, two oxidation xeaatiorts have to be considered. Firstly, the oxidation of copper to cuprous oxide:
~l[Cu~anoy 'E- ~z (g) -; 2Cu20 (s) t1) Secondly, the oxidation, of germznium tv gerrmxnium {di)oxide:
[~''le~~lloy ~ 02 (f) '~' ~~d2 (5) The above equation shows formation of germanium {1V) oxide, Ge02, but there may also be formed germanium (1l) o:dde, Ge0 or an intermediate material Ge,;Oy where x is 1 and y is greatex tht~n 1 bttt less than Z. Under standard conditions, i.e. for pure Cu and pure Ge each reacting with pure oxygen gas at tttm pressure to forms the pure oxide phase, both reactions are feasible, with the chemical driving force for xeaction~ (2) being hi;her than that of reaction (1) by a factor of 1.65.
Accordiatg to Wn 01095082 (Johns) tarnish resista~zGe ofternary alloys of silver, copper and gern~azZiunl or quaternary alloys of silver, copper, Zinc and getmatrium can ho increased by casting a molten mixture to form the alloy and annealiz~ the alloy to reduce its thielcnoss and rc-crystalline the trait's in tlm ahoy, the annealing being carried out under ~. selectively oxidizing atmosphere e.g HzIH20 or COICOz iv pxomote the formation of GeOz while preventing the formation of Cu20.
~'raatnient coxxApasitions for removing br pre~Veutielb silver tarnisv Various proposals have been made for cleaning or protecting Sterling salver and other known grades of silver to rexnove tarnish t~ridlpr to inhibit the t o Poxmation of tarnish.
US-!~-2841501 discloses a silver polish based on z1n abrasive powder and a C12-Czo n-atkane thiol which is said to be nonytoxic, to have a mild odor and to protect silver against tarnishing by fdr~ning a manomolecular layer R-S-Ag 1s wherein ft represents the alkane chain of the thiol, said Iayer forming a physical barrier between t1e silver and reactive ingredients of the atmosphere.
GI3-A,-1130540 is concerned with the prot~etion of a finished surface of Slerlir~ or >3xitannia silver as a step in a production run, and discloses a process z0 that comprises the steps of wetting cz clean silver surface of an article v~dth a solution comprising 99 parts by weight of a volatile organic solvent, for e~:ample trichloroethylene or 1,1,1-trichloroethane and from O.I-1.8 parts by weight of an organic solute containing a -SH group and capable of forming a transparent colourless z5 pxotective layer on, the silver surface, for example stearyl and cetyl ~ercaptan or thioglycollate;
allowing the solution to react with the surface to form such a layer .and allowing the solvent to evaporate; and vrashzng the surface with a deterge~~t solution, rinsing the suxface with hot 30 water and allowing it to dry. The above process is stated to provide a "long-term finish" intended to last the intended shelf life until the article reaches the user.

Halohydrocarbons 'were said to be the xzaost suitable solvents but theic~
suitability on environmental growtds is now open to ciuestion. Lthers ~Yere said lU
be flanunablc and toxic, and lo~,ver alcohols were said to be poor solvents.
VTater is not mentioned as a soIverrt. Applicants have seen a report on the Internet fCOm s ATQ'FINA Cherz~icals lnc that the solubility of mereaptans in water decreases progressively from 23.30 gllitre for maihyl mercaptan to 0.00115 gllitre for nonyl mercaptan, and data for for both hexadecyl and octadecyl mercaptan {CAS 2$85-00-9) reports them as water- insoluble.
tU US-A-61S381S (Snick) also teacbes that treatments of the above kind are xesult in the fuzxnation of a saltassernbled coating derived fzom the thiol compow~ds in which tha sulphur atoms are bound onto the metal surface and the allryl tails ore directed pwuy from the metal surface. In the examples of that specification, iluoroaIkyl arnides e.g. CFa{CFz)sCONH(CH2)ZSH iri aqueous is alcohols e.g_ aqueous isopropanol are sprayed auto the surface of silver, after which the surface is rinsed ttnd dried with a salt cloth. The fluoraaikyl amides lank detectable odour and can dissolve in lower alcohaIs or alcohoilwater mixtures, although it is apparont from the description and examples that not all alcoholic solvents prod .t~ce good films.
2tI
Yousong lCim et a! repvrl that the adsorption of thiols onto silver proceeds through an anodic oxidation reaction that produces a shift of the open circuit potential of the substrate metal irt the negative diz~ction or if the potential is f xed an anodic ctu-rent peak:
25 RSH -t-1~(0) --> RS-1vI(I) + 1h' + a (M) {M = Au or Ag), sae httwllt-vHVV.elecJrachem.or lm~ eetirt~sl,~ast1200/ab ~t~ raclsl_ SaYmpcsiylhlll026 pdf KWEiIl K11T1, AC~SDY~7lTUi1 v?itc~ lteactioyi of Thlots aYecl S2rlfide5 ort Noble Nletals, Rarxzan SRS-2404, I4-I7 Au~ast 2000, ~.aimen, Fujian, China, 30 Itttx~;//I?coss.orgricoz~sxtnlpaper~7cut~t~cim.pdf , also iliscIuses the formation of self-assernblecl morsolayers and discloses that alkanetliols, diaLl;yl sulfides and dialkyl disulfides self assemble on silver surfaces with aliphatic dithiols farming dithoiolates by forming two Ag-S bonds.
In oontr~st, the literature an formation of alkylthiols of germanium is relatively sparse, The dissaciztive adsorption of H~5 at a Ge I00 sttrfS.ce to yield adsorbed -SH groups and adsorbed hydrides has been raported by 3~lelen e~ al., .lpplred Surface Science. 1.~0, 65-72 (1999), see htto~/lv~ww.chem.missauri.edu/Greenlief/aubslOD005797.gdf.~ see also a report by Professor Michael Cxreenlief of the University of Missouri-Coluarbia t0 http:lhvww chetn rt~i~souri.edulGreenlieflReseareh.htm3 that room te~nnperature exposure of H2S to Ge(14D) results in dissociative adsorptiUn that can be fol3owed easily by ultraviolet photoelectron spectroscopy. The reaction of alkanethiols with Ge to farm a high quality monolayer has been reported in the context of semiconductor and nanoteehnolo~y by Han et al, .l. .4m_ Chem. Soc., 123, 2422 (24Q7.), In the experiment described, a Ge(111) wafer is sonicated in acetone to dissolve organic contaminants and immersed in Concentrpted HF to remove residual oxide and produce a hydrogen-terminated surface, after which the wafer is immersed in an alkanethiol solution in isopropanol, soz~icated in pzopanol and dried.
z0 S~)IvrMAI~Y OF THE INVENTION
Althou~li GB-A-1I30540 was alleged to provide a Long-tenor finish, the experience of one of the inventors who is a silvexsniiih is this type of treatment z5 does not fully solve the difficulties Created ny tarnish in the period between manufacture and supply to the ultimate purchaser or user and suffers from a number of shortcomings. A.Ithough a silver prtsduct might arnve at the retailer in an untarnished state, it was largely tho result of the wrapping applied by the manufacturer, which protected the article from air. Once the wrapping was 3o removed and the article was displayed in a retail environment such as a display case in a hotel where it was subject to ambient air and the heat of artificial lighting, an article of conventional Sterling silver would require rc-polishing after one week and after two weeks t~rou.ld normally be so tarnished as to be un-saleable. At an e.Yhibition, the life of an article on display before significant tarnish sets in may be as sham as 3-4 days. Re-polishing produces wear and fine handling scratch~;s, so that unless the article can be sold quickly it looses its pristine appearance. The need to polish display silver at frequent intervals adds to the labour cost of a jeweller or other retail establishment, whose management take the view that its staff should be employed to sell producas and not to clean stock.
Tamis'b at point of sale or display is therefoxe a serious problem that reduces the to willingness uF those in the distribution chain to stock and display silver products, and which has not yet been adequaiely solved.
V~hen the product reaches the ultimate putcl~aser, it is of course desirable that the t<~sk of tarnish removal should be made as infrequent anti undemanding ns pnssible.
silver alloys according to the teaching of GB-E-22~53~8 and EP B-0729398 are now commercially available in Europe and in the LTSA under the trade mark Argeniium~and the word ".Argentium" as used herein refers to these alloys. Although they e:rhibit improved tarnish resistance compared to e.g.
Sterling silver, and any tartzish that forms can be removed by simple washing, there is still room far improvement in tarnish resistance. 'fizat rc.~nains true even when annealing is conducted in a selectively oxidising atmosphere as disclosed in WQ 02/0950$2.

It has now been found that an alkanethiol, alkyl thioglycollale, dialkyl sulphide or diall:yl disulphide Gan be used for the surface treatment o~ an allay of silver containhtg an amount of germanium that is effective to reduce frestain andlur tartushing so as to reduce or further reduce tarnishing of the alloy such tlaat a sample can be subjected to hydrogen sulphide gas above a 20% solution of .. C
ammonium polysulplude for at least 30 minutes and typically ~5-60 minutes al room temperature while retaining a generally untarnished appearance.
The invention therefore r4lates to ~r method for treating a finished or semi-s finished shaped flatware, hollowware or jewellery article of a silverlgermanium alloy that has a silver content~of at Ieast 77 wt % and a germanitun content of bctrveen 0.4 and 7°~° the remainder principally being copper so as to reduce or further reduce tarnishing of the article such that a sample or the alley of which the article is made can be suppaz~ted close above a 20% solution of ammonium 1b polysulphide for at least 3~ minutes while retaining a generally untarnished appearance, said method comprising surFac:e treating said article with an alkanethiol, alkyl thioglycollate, daalkyi sulfide or dialkyl disulfide 15 The above method may include tire further step of introducing the article into packaging.
The invention further provides a finished or semi-finished shaped flatware, hollowware ~r jewellery ariiGle of an alloy of silver containing au zo amount of germanium that is effective to reduce firestain andlor tarnishing and that ha,~ been treated with a C,2-C~4 allcanethiol, alkyl thioglycollate, dialkyl sulphide or dialkyl disulplude and that exhibits a tarnish resistance such that a sample of the alloy of which the article is made can be supported close above a 20°/a solution of ammonium polysulphide for at least 30 minutes while retaining a 25 generally untarnished appearance.
The above accelerated tarnish test in which the article is subject to hydrogen sulphide gas front the amrnonim polysulphide solution above which it is suspended at a height of e.g. 30mm correspozrds to a period of a year or more in 3o a retail environment where an article is on display and e;~posed to ambient atinosphes~e and may be subject to elevated temperatures. It is the combination of - la the protective Function of the germanium content of the alloy with the further protection from the argatto-sulphur compound that is believed to be responsible for the observed increase in tarnish resistance. 'The period during which the article zetains its untarnished Appearance under these severe conditions may be three or s more tithes the corresponding period for an article that has not been treated with an organo~sulpnur compound, ivhieh is unexpected because the same accelerated tarnish test carried out under the same conditions vn a. conventiozu~I
Sterling silver article not containing protective gcrnxanium does not reveal a siSnif Cant increase in untarnished lifetirxte between its untreated and angora-sulfur treated states.
t0 Accelerated tarnishing trials carried out using Argentium and standard Sterling silver samples immersed in solutions of octadecyl merc3ptan and hexadecyl mercapte~n Imve shown that the protective thiol is removed from the standard Starling sample but not from the Argentium silver samples on rubbing with a tissue soaked in a solvent (EnSolv 765, an n-propyl bromide based solvent ~3 cleaner discussed below), 1n accelerated testing the solvent-rubbed regions of standard Sterling silver discolour more rapidly than the un-rubbed regions whereas in Argentium silver no noticeable difference in. appearence develops between the rubbed trnd un-rubbed regions, suggesting that thiol bonding is stronger or more effectjwe.
AcceIer-ated tatztishing tests with Argentium Stezling using amrctonium polysulphide have been reported by the Society of American Silversmiths, see htfi~/lwww ~ilversmithit~,~ comll or entium4 httn and in a comparative test the Argentium Sterling remained untarnished after one hour whereas conventional Sterling became tarnished alter less than 1S
minutes.
However, in this test 0, 5mI of 20°lo atnmanium polysuifide solution is mixed with 2UUml of distilled water, so that the test is ;neatly less severe than when samples are exposed to the 20% solution itself. In WO 0~1Q95082, samples ware ' suspended above 20% amnronium polysulphide, but the exposure times were 3o relatively short, and onset of yellowing was reported for Ag-Cu-Ge allays after 3-5 minutes exposure. Other tests reported it7 that specification involve placing samples irz a clesiccator containing flowers of sulphur ~.id calcium uitxate and are less severe than the ammonium polysulphide test.
As part of their program for developing improved fbrn~ulatjoz~s for tl3e s treatment agents described above, the applicants have unexpectedly discovered that the treatment agents cari be dissolved ar dispersed directly in aqueous surfactant without the need far preliminary dissaiving of the treatment agent in an organic solvent and sui~sequent mixing of tlae zesulting solution with aqueous liquid. >rmbodiments of the above compositions sue optically clear and storage-stable at ambient temperatures for a period of weeks or months. The treatment composition uiay therefore be water-based and comprise an alkanethiol, alkyl thioglycollate, dialkyl sulfide oz dialhyl disuit'ide and a mixture of an anionic surfactant with a. neutrat or arrxphoteric surfactant and water.
i$

D)~TATh.)CD AESCIt~TION OIf T~ I1~IVENT1G~1 Silver-copper-germanium alloys s The allays that may be treated according to the invention include an alloy of silver conta,inin,~ an amount of germanium that is effective to reduce Brestain and/or tarnishing. US-A-6406664 (l7iamond~ discloses that amounts of germanium as low as O.lwt% can be effective provided that substantial amounts of tin are present but although formulation examples are given, no test data for corrosion or firestuin is given either for articles made by coating or fox articles fabricated from sheet. The inventor considers that 0,5. wt% Ge provides a preferred and more realistic lowex Iitnit pod that in practicE use of less than lwt°/'o is undesirable. A two-component coppex-free alloy could comprise 99°l0 .:1g and t Ge, and a #arttish-free casting alloy for jewellery kas been reported that comprises 2.5°.'°Pt, 1% Ge, balance Ag and optionally containing Zr, Si or Sn.
The ternary Ag-Cu-Ge alloys and quaternary Ag-Cu-Zn Ge alloys that can suitably be treated by. the method of the present invention arc those having a silver content of at least 30%, prererably at least 60%, mare pxcfcrably at least 80%, and roost preferably at least 9?.5%, by weight of the alloy, up to a maxitniun of no more than 98%, preferably no more than 9?%. The gennaniurn content of the Ag-Cu-(Zn)-Ge alIpys should be at least 0.1%, preferably at least 0.5%, more preferably at least 1.1 %, and most preferably at least 1.5°/, by weight of the t~lloy, up to a maxirnum of preferably rio more than 6.5%, morn preferably 2s no more than 4%.
if desired, the germanium content may be substituted, in pact, by one or more elements which have an oxidation potential selected from At, Ba, Be, Cd, Co, Cr, Er, Ga, h~, Mg, Mn, Ni, Pb, )?d, Pt, 5i, Sn, Ti, V, 'Y, Yb and Zr, provided the effect of germanium in terms of providing f res#ain and tarnish resistance is not unduly adversely a~ff~cted. Tlxe weight ratio of gennpniwo to substitutable elements may range frort~, x00: 0 to 40; 40, preferably from 100: Q to $0_ 20.
Preferably, the gercnarzium content consist entirely of germanium, l. e. the weight ratio is 100; 0.
The remainder of the ternary Ag-Cu.Ge alloys, apaxC from impurities and any grain refiner, will be constituted by copper, which should be present in an amount t~f at least 0.5%, preferably at least 1°fo, wore preferably at Ieast Z°lo, and most preferably at least 4%, by weight of the alloy. For m '$Q0 grade' ternary alloy, for example, a coppex content of 18.5% is suitable. 'I~e remaindex of floe to quaternary A,~-Cu-Zn-Ge ahoys, apart from impurities and any grain retainer, will be constituted by copper which should be present in an. amount of at least Q.5°/v, preferably at Icast 1%, more preferably at least 2%, and most preferably at Ieast ~%, by weight of the allay, and zhtc which should be present in a ratio, by weight, to the copper of no more than 1: 1. Therefore, -zinc is optionally present in the silver-copper alloys in an amount of from 0 to 100 % by weight of the Copper content. For an '$00 grade' ttuaternary alloy, for cxarnple, a vopper content of I0.5% and zinc content of 8°f° is suitable.
In addition to ,silver, popper and germanium, and optionally zinc, the alloys preferably contain a grain refuxer to inhibit grain growth during processing of the alloy. Suitable graitz refiners include boron, fridittm, iron and nickel, with boron being particularly preferred, The grain refSner, prefCrably boron, rnay be present in the Ag-Cu (Zn)-Ge alloys in the range from I ppm to 1~ ppm, preferably from 2 ppm to 50 ppzn, txioxe preferably from 4 pprn to ZO pprn, by weight of the alloy.
In a przferred eznbodinzent, tha allay is a ternary alloy consisting, apart from impurities and any grain refiner, of 80°/a to 96% silver, 0, 3 °ta to >%
germazuum and 1 % to 19.9% copper, by waight of the alloy. In a more preferred 3o embodiment, the alloy is a ternary alloy consisting, apart from impuriiies and grin rcfiuer, of 92.5°,~o to 98%v silver, 0.3°~o to 3% germanium and 1% (v 7.2%

s copper, Gy weight of the alloy, together with 1 ppm to 4U ppm haxon as grain z~~n er. Zxz a further pret~rred embodiment, the alloy is a ternary alloy consisting, apart fnon~ impurities nnnd gain refizmr, of 92.5% to 96ro silver, 0. 5% to 2%
germanium, and 1 %u to 7% copper, by weight of zl~e alloy, togethex with 1 ppm t~
40 ppm boxon as grain refiner.
ProteeEive itgents As protective agent there may be used a compound cotztainit2g s long io ahairz alkyl gxoup and a -SIB ox-S-S- group, e.g. an alkancthiol, dialkyl sulfide or dialkyl disulfides in which the chain is preferably at Least It) carbon atoms long and may tae Cz2-C24. The -STI or -S-S- compounds that many ba n,secl znclt~de straight chain satuxt~ted aliphatic corupouuds containing 16-24 oarbon atoms in the chain, for example cetyl znercaptan (hexadccyl. mcreaptan) and stearyl morcaptan (ocGadeeyt mercaptan) and cetyl aztd steary~ thioglyeoliates whose forrnuiae appear blow.
HS
HS
4ctadecyl mercaptan is a white.to pale yellow waxy solid that is insoluble in water and that melts at 15-16°C. Hexadecyl mercaptan is also a tvhitc or pale ?5 yellow waxy solid that melts at 30°C, formulations based au organic solvents The prvteetivc agent may be used in solution in a solvent e.g. a non-polar orgaziic solvent such as an alcohol e.g. methyl or etlryl alcohol, a ketone e.g.
3 acetone or methyl ethyl ketane, nn ether e.g. diethyl ether, an ester e.g. n-butyl acetate, a hydrocarbon, a ' haiocarbon e.g. methylene chloride, l,l,l-triehloroetlYane, trichloroethylene, perchlorosthylene or HCFC 14I b. The protective agent may comprise 0.1-1 wt°/n of tt~e soivent. Sfllvents based on alkyl or aryl halides may be used e.g. n-propyl bromide which is pxesently preferred on z0 the ground of the short atmospheric life of that compound, its relatively low ~toxieity corrzpared to other haloosrbons, its favourable chemical and physical propazBes and its boiling point, specific heat and Latent heat of vaporisation_ US-A-56t6549 discloses a solvent mixture comprising: 90 percent to 15 about 96.5 percent n-propyl bromide; 0 percent to abocit 6.5 percent of a mixture of tcrPcnes, the terpene mixture comprising 35 percent to about 50 percent cis-pinane and 35 percent to about SU percent trans-pinane; and 3.5 percent to about 5 percent of a mixture of low boiling solvents, the low boiling solvent mixture comprising 0.5 percent to 1 percent nitromethane, 0,5 percent to 1 pexccnt 1,~-20 butylene oxide and 2.5 percent to.3 prscent 1,3-dioxolane. The solvent mixture has the following attvantages;
(l) it is properly stabilized against any free acid thQt might re;;~ult from oxidation of the mixture in the presence of air, from hydzolysis of the mixture in the presence of water, and from pyrolysis of the mi.Yture under thi influence of 25 high tempezatures;
(ix) it is non-flammable and non-corrosive;
(iii) the various components of the solvent mixture are nvt regulated by the CJ.S. Clean Air Act; and (ivy none of tlxe various components of the solvent mixture are known 3o cancer causing a4ents (i,a., the various components are not listLd by N.T.I., LA.R.C. and California Proposition 65, nor are they reguated by ~SHA).

~j 1~'Ivrev~er, the salveiit mixture has a high solven~Gy with a kauri-butanol value above 12d and, more preferably, above 125. In addition, the solvent mixture has an evaporation rate of at least ~,9fi where 1,1,1-Trichloroethane=1, Upon evaporation, the solvent 171LYt111P~ leaves a non-volatile residue (NVR) o1' less than 2.5 mg and, more preferably, no residue, Solvents made in accordance with the above patent are available from Enviro~Tech International, Inc of Melrose Park, IlliIlOAS, lJSA under the trade naare EnSolv.
Farraulatior~s based on organic solvent and W~tGx IQ
For many purposes, e.g. light industrial applic~.tions, it may be preferred to carry out the anti-tarnish treatment using a predominantly aqueous solvent system, For this purpose, the protective agent may be dissolved in a water-immiscible organic solvent, for example a solvent based an n-pzopyl bromide, the resulting solution may be mixed with a relatively concentrated water-based soap or detergent composition which acts as a "carrier", after which water is added to the resulting mixture to provide an aqueous treatment dip or combined degreasing and treatment solution. Thus an aqueous dip has the advantages that a solvent degreasing system is npt necessary, the dip is easily made and may ba used cold, 2o alt areas of immersed articles Can come into contact with the stearyl rtrercaptan or other treatment aSent, Argentium Silver only requires 2 minutes - 1 hour in the dip, rinsing and drying of articles are made easy as water droplets are repelled tiom the surface of the polished silver, and the clip cart be easily used in a manufacturing environment before articles axe sent to retailers.
Preferred water-based detergents may be based on anionic, alkaxylated non-ionic or water-soluble cationic surface active agents or mixW res of them and preferably have a pH at or close to 7. Anionic surfactants may be based on alkyl sulphates and alkyl benzene sulphonates, whose harshness on prolonged skin exposure may be reduced by the ca-presence or use of alkyl ethox.y sulfshates (US-A-3793233, Rose et u1.; 404075 Gilbert; 431 S82a Pancherni). Other kno~,vn s«rfactants e.g. betaines may also be present, see e.g. US-A-4555360 (Bissett). A
suitable i~oulation cc>z~taiz~,zo.g S-15 wt% non-ionic surfactants and 15-3d wt°/a anionic surfactants is available cornnaercially in the UK under the trade name Fairy Liquid (Praetor & Gamble).
An aqueous liquid may~also be made by dissolving the treatmvent agent il~
a non-organic solvent and adding a relatively concentrated aqueous detergent liquid, fox example undiluted Fairy Liquid, This provides a detergent liquid that has a number of advantages: the soapy liquid is easily made, the liquid is easily to applied to the Argentium Silver articles with a damp sponge/cotton wool/cloth rte, the liquid and lather enables the stearyl tnercaptau or other treatment agent to get into those awkward areas on are article where a cloth may not be able to xeach, riming and drying of articles are mach easy as water droplets are repellod from the surface of the polished silver, the process can be easily used in a.
t 5 manufaoturing environnxent before articles are sent to retailers and cQn also be easily used in a retail or domestic environment. Furthermore, the hydrophobic properties imparted to silverlsilver alloy on treatment with the present thiol-based treatment agents may alleviate ox overcome the problems of water-marks or water-stainuag from , rinsing processes in a manufacturing or domestic 20 environment.
~ornaalations bused on aqucoets liquids it has surprisingly bean found that formulations containing effective zs amounts of the treatment agents Gan be made by dissolving the~u directly in aqueous liquids containing an anionic and s. nexttral or araphoteric surfactant and free from water-immiscible organic solvents and preferably free from alt other solvents. 'fhe treatment agents may be dissolved in xalatively concentrated -swfactaz~t-co~ntainxng adueous liquids, which may be used as such or a#ler 3o subsequent dilution with -water, see in particular the instructions given in the preceding section.

t 'fhe treatment agent may be present in said composition, prior to dilutiuan thereof, in an amount of at (east 0.1 wt % and preferably at least 1 wt %, the solids content of the composition being at least S wt %, typically 3 0-4Q
wt and possibly 50 w(% or mole. The ability of aqueous sui~faetant liquids to dissolve or disperse such relatively hig"ci concentrations of higher alkyl thiols and other treatment agents which are repoxted to be highly water-insoluble has not been described. The resulting concentrates may be diluted with water to provide an aqueous treatment dip ar combined degreasing solution and dip for use as explained above, and it has been found that the treatment agent may remain in l0 solutivrc yr suspension following such dilution and may remain effective for the surface 2reatnxexit of silver-copper or silver-copper-germanium alloys and possibly o~tler metals such as copper, brass and nickel where surface protection films may retard corrosion. Particularly good results from the stability and effectiveness standpoint may be obtained by mixing hcxadccyl mcrcaptan (in the liquid state) straight into a surfactant "carrier" and using the solution as such or on subseqtreztt dilution with watex.
In particular, the present treatment agents can be successfully dispersed in aqueous liquids contairfmg mixtures of neutral and anionic suxfact~zr~ts with the 2o neutral surfactants providing e.g. about 33 w(% of the totfd surfactant present.
Treatzt~ent agents that cans be dispersed in such agents include n-hexadecyl thiol and n-octudecyl thiol. They crzn also be successfully dispersed in aqueous liquids containing mixtures of arnphoteric or zwiterionic surfactants and anionic si,u~'actants and such mixtures can provide relatively storage stable optically clear solutions witlx little or no tendency to re-precipitate the treatment agent.
In that case the weight ratio of the arnplrateric or zwitterionic surfactant to the anionic surfactant may be from I :I O to 10: l, typicsliy close to 1:3.
Anlphvteric or zwitterionic surfactants that may be used alone or in 3o admixture with one another arrdlor with nonionic surfactants and,~or with anionic surfactants rnay ba derivatives of secondary or tertiary amines, derivatives of heterocyclic secondary and tertiary mnines, ar derivatives of quaternary ammanimn, quaternary phasphoniunn or tertiazy sulfonium compounds. The cationic atom in the duaterrtary compound can be part of a heteroeyelic ring, In alI
of these compounds there is at least one aliphatic group, stralglxt chain or branched, containing from about 3 to 18 carbon atoms and .pt least one aliphatic substitucnt containing an axiionie water-solubilixing group, e.g., carboxy, sulfonate, sulfate, phosplzate, or phosphonate.
Examples of zwitterionic surfactants that may be employed include betaine surfactants, which are preferred, imidazoline-based surfactants, axnirioatkdnoate surfactants and in ~inodiallkaaoate surFactattts. S~zitable such surfactants include amidocarboxybetaines, such as cocoamidodiznethylcaxboxymethylbetaine, Iaurylamidodimelhylcarboxymethyl-betaina, celylam3dadimathylearbo:cy-methyibctainc, and coc4arnidd-bis-(2-hydroxyethyl)carboxymethyl-betaine. Particularly preferred are arnidocarboxybetaines betaines of flee formula below wherein R xopresents Ca-Cps alkyl e.g. cocanudopropyl betaine. That compound is generally regarded as safe:
in axz Aznes test conducted by BASF it did zzot prove mutagenic to Salmonella indicator organisms and in a human repeated patch insult Lost (APT) it did not indicate either contact hypersensitivity or phatoallergy (see the IvIAFC? CAB
cocaeaidopropyl amino betaine data sheet published by BASF):
N~'' o o ~N Q-/R
Also useful are sulphobetaine stlzfactants, e.g amide sulfabetaines such as ?5 iauramido-sulfoprapylbetaine of formula indicdfcd below, cacamido-2-hydroxypropylsulfobetaine, coeoaznidodimethylsulfopropyl-betaine, stearylamido-dimethylsulfopropytbetainc, and laurylamido-bis-(2-liydroxyethyl)-snlfopropylbetaine. Ellso useful may be imidazoline-based surfactants including .
s gylcinate and arnphoacetate compounds e.g. cvcoamphocarboxypropivnate, cvcoarrtphocarboxyprapionic acid, cocaamphocarbaxyglycinate, and cacaamphoacetate, aminoalkanoRte surfactants e.g. n-alkylamino-propionates and n-alkyliminodipropionates such as N-lauryl-(~-amino propionic acid and salts thereof, and N-Iauryl~~3-izzxino-dipropionic acid and salts thereof:
ton-ionic surface-active agents that may be used alone ar in admixture include compounds produced by the condensation of an alkyleim oxide with an w organic hydrophobic compound that may be aliphatic or alkyl aromatic. The length of the hydrophilic or polyoxyalkylene moiety that is condensed with any i5 particular hydrophobic compound can be adjusted to yield a water-soluble compound having the desired balance bctwoezr hydrophilic and hydrophobic moieties. Seuii-polar nozzianic surface active 'agents may also be used, including a~zZine oxides, phosphine prides, and sulfoxides. Suitable classes of compound include;
z0 ~ Polyethylene oxide condensates of alkyl phenols. These compounds include the condensation products of alkyl phenols having an alkyl group containinø
from about 6 to 1 ~ carbon atoms in either a straight or branched chain, with ethylene oxide, the said ethylene oxide; being present in amounts equal to 5 to ~5 tz~ales of ethylene. oxide per mole of alkyl phenol. The alkyl substituent in such COmpDUndS may be derived, for example, From polymerized propylene, diis4butylene, octene, or nonerae.
~ Condensation products oY aliphatic alcohols with ethylene oxide. The alkyl chain of the aliphatic alcohol may either be straight oz' brtuzcf~ed and generally contaitta from about $ tv about 22 carbon atoms Coudelisatian products of ethylene oxide vyith the product resulting from the reaction of propylene oxide and ethylene diatiiine.
~ Atnine Oxide surfaat<~ts, for example dimcthyldodecylamum oxide, dimefihyltetradecylatnine oxide, ethyhncthyltetradecylamine oxide, cetyLdimethylamine oxide, dimethylstearyl~mine oxide, cetylethylpropylamine oxide, diethyldadeGylamine oxide, diethyltetradecylamine o:cide, dipropyldodecylamine oxide, bis-(2-hydroxyethyl)dodecyiamine oxide, his-(2-hydroxyethyl)-3-dodecoxy-2-hydroxyprapylamirie oxide, (Z-hydroxypropyl)methyltetradecylamine oxide, ditnethyloleylamina oxide, dimethyl-(2-I~yd~oxydodecyl)a~ine ~xido, and thw corresponding dec:yI, hexadecyl and octadecyl homologs of the above compounds.
Phosphine oxide surfactants, e.g. din retlryldodecylphosphineoxide, dimethyltetradecylphosphine oxide, ethylmethyltctradecylphosphineoxide, 2o cetyldin~ethylphosphine oxide, dimethylstearyIphosphineoxide, cetylethylpropylphosphine oxide, diethyldodecylphosphineoxide, diethyltetradecyLphospbinc: oxide, dipropyldodecylphosphineoxide, diprvpyldodecylphosplzlne oxide, . bis-(hydroxymethyl)dodeeylphosphine oxide, bis-(Z-hydraxyethyl)dodecylphosphine oxide, (2-z5 hydroxypropyl)methyltetradecylphosphine Oxide, dimethyloleylphosphine oxide, and dimethyl-(2-hydroxydodecyl)phosphine the oxide and corresponding decyI, hexadecyl, and oct0.decyl hnmoiogsabove of the compounds.

Sulfoxide surfactants, for example oc;tadecyl methyl sulfoxide, dodecyl 30 methyl sulfoxide, tetradecyl methyl sulfoxide, 3-hydroxytridecyl methyl sulfoxide, 3-n~ethox5~tridecyl methyl sulfoxide, 3-laydroxy-~t-dodecoxybutyl methyl salfoxide, octadecyl 2-hydraxyethyl sulfoxide, and dodecylathyl sulfoxide.
~ Ethanolamide-based surfactants e.g. coconut fatty acid monoethanolamide or diethanolamide.
wherein R represents C~o-G.ao, ~p Gtz-Gis allLyl e.g. ulsyl- or coco-, rurther surfactants tray be based on diethylene triatnine (DETA)-based quaternaries, such as diamidoamine ethoxylates and irnidazolines, and esterquats. As a class, asterquats can be based an compotmds incltuiing methyl diethanolaniine lo (tvIDEA), triethanolamine ~TIiA?, and N,N-dirnethyl-3arninopropane-1.,2-diol (DMAI'D).
A wide variety of alkyl sulfates may be used as anionic surface-active agents including fatty alcohol sulphates, fatty alcohol ether sulphates, alkyl IS phenol ether sulphates, alkyl aryl sulphoniG acids and salts (hereof , cusnene, toluene and xyle~ne sulphonates and salts thereof and alkyl sulphosuccinates e.g.
soditun or ammonium lauryl sulfate, However, a preferred elttss o~ anionic s~~rface active agents is polyol monpalkylether sulfates of the formula RQ-(GHZCHz~S03M whez~in~~ represents Cao-C:1& alkyl, n is 2-6 (preferably about 2-2Q 3) and M represents a rnanovalent ration. Such compounds ure sulfonated ethoxylated C,o-Crs alkahols which may be derived from coconut oil or tallow of may be synEhetia. Sodium lauretk sui.fate which has beer! used succcssferlly herein is a sodium lauryl ether sulphate ethoxylated to an average of two moles of ethylene oxide per mole of lauric . acid and sulfated, and is of fortvula zs cH,(cz~z3~~cHztoc~z~G~rzhoso3Na.
In addition to sirrtple treatment agents, the above compositions may be formulated into mefal polishes e.~. for silver or brass. Suc$ products may be formulated as llLlufd prOdllCt5 lllt0 w171Ch objects such as jewellery ox cutlery are 30 to be dipped. After dipping, the objects are exsuahy rinsed under water and dried _ '1~ _ with a soft cloth. Alternative formulations take the form of creams or pagtes which are applied with a soft cloth and then z~er~.ioved.
Tor formulation into dipping composition, the active ingredients axe s normally an acid having a pKa of not more than ~, c.g, phosphoric, citric, oxalic, or tartaric acid together with thiourea or a derivative thereat e.g. an alkyl derivative such as methyl or ethyl thiourea. For formulation into creams or pastes there znay be e.g. about 25 wt°/a of a mild abrasive such as precipitated chalk, infusorial earth, silica or ~-aluinina (e.g. 0.05 tun grade). These ingredients are i4 believed compatible with the surfactants and treatment agents and can be incorporated when convenient by simple mixing.
Treatment procedures i s The surface treatment nzay be carried out after the manufacturing stages for a shaped article made of the alloy have been completed. The article may be of flatvsrare, hollowware ar jewellery, Fabrication steps xn.ay include spinning, pressing, forging, ousting, chasing, hammering from sheet, planishing, joining by soldering braying or ~yelding, annealing cad polishing using bmffslmops and 2o aluminium oxids or rouge.
An article to be lrea.ted may be de-greased by various methods:
~ Vapour degreasing with or without ulirasonics ~ Aqueous degreasing wish or without ultrasonies 25 ~ Organic Solvent C18~'8lslllg with or without ultrasunics (e.g. degreasing with ethanol or acetone poor to thiol trcatancnt which may provide very goad accelerated tarnish test results)_ ~ Simultaneous degreasing and thiol treatment, the thiol being present in an organic or adueous degreasing medium.

por example, the artxcIc may be degreased ultrasonically in ~. treatment bath, dipped into a bath containing the treatment agent e.g. 1 wt% steaxyl mexcaptan in solvent e.g. IanSolv, rinsed in one or more baths of the solvent and allowed to dry by cvapotation. Rinsing excess thiol away with the sane solvent s that is used for thiol treutiiicnt is preferred, so that tlliols that have not reacted with the metallic surface are removed and are unavailable to react with anything else. The solvent should leave no or substantially no residue, so that subsequent washing with water or aqueous solvents should be unnecessary and the article cari be allowed to dry. The article xuay then he packed for delivery into the i0 distribution chair. This may include u~apping the article in one or more protective sheets, placing it in a presentation box, and wrapping the presantaticn box in a protective wrapping e,b, or heat-shrunk plastics film, Articles which have been treated with au organic compound 4ontaining -SH or -S-S- groups as aforesaid and packaged should not only reach their point of sale in goad Condition t5 but should if displayed e.g, on a shelf or in a cabinet for a~~ exter:ded period, expected to be at least 6 months and possibly 12 months or more, remain without development of significant tarnish.
The articles may~.lternatively simply be polished with a polish containing z0 1-5wt% of the organo-sulphur compound e.g. stearyl mercaptan together surfactants and a cleaning agent e.g. diatomaceous earth in a solvent. As a further R.Iternative; they may be simply polished with a cloth impregnated with the sogano-sulphur compound e.g. cetyl or stearyl ruercaptan e.g by impregnation with a treatulent agent in an organic solvent e.g. n-propyl bromide followed by 2s drying, The advantages of a Cleaning cloth are that it is easily manufactured, eau he aasil~~ used in. a xetail or domestic environment and is good for general upkeep ofArgentium Silver (if required).
Tl~e treatment mothort of the invention would fmd paz-titular benefit in the 30 tarnish protection of blanks for stamping coins immediately before the st<~mping operation because it has beers found that embodiments of the present films can largely or wholly survive the stamping operation and can provide pritection against tarnishing for the newly rr~inted coins. It will be appreciated that coins in mini cvnditian are packaged far collectors with minitnsl handling, and that every ocasion of handling e.g. polishing with a saft cloth involves risk of damage to the coin, The rislt of such damage is reduced by the present treatlzienf which can impart prolonged tarnish resistance.
Tl~e invention will now he further described, by way of illustration only, with reference to tlae following exannples. Throughout the examples, the term "~;.nhanced tarnzsh resistance" of samples treated with stearyl mercaptan refers to the eomparisan with samples of A,rgentium 5ih~er which have not had any ireatmer~t except fcr polishing and degreasing.

Example 1 Soivenf dip application (solvcnf degreased samples}
s Solutions were made up containing stearyl mercaptan {0.I, 0.~ and l.0 gram) in EnSolv 765 (100 ml). Samples of Argentium Sterling Which had been polished and ultrasonically degreased in EnSolv 765 for 2 minutes were each.
immersed in one of the stearyl mercaptan solutions for periods of 2 minutes, 5 minutes and 15 minutes. The samgles were then buffed with clean cotton wool.
In order to evaluate tarnish resistance, dZe alloy samples were supported on a glass slide in a fume cupboard about 25mm above the surface of 20°/
annnnoniurrz polysulphids solution so as to be exposed to the hydrogen sulphide that arises from that solution. All of the samples demonstrated good tarnish resistance during a one-hour test; with vary slight yellowing after 4S minutes exposuxe to the hydrogen sulphide. The light film on the satzrples was easily removed with a cleaning cloth impregnated with stearyi mercaptatz.
By ~teay of caparison, a standard Sterling silver sample started to zo discolour as soon as it was subjected to the above test and alter one hover had formed a heavy black taztush which could not be removed with a Cleaning cloth ii~iprognated with steary! rnerc:aptdn. The xesults obtained with x second Starling silver sample that had been wiped with the cleaning cloth were similar dad discoloration started as soon as the sample had been placed into the test. An Argentium StErling alloy produced in accordance with EP-B-0729398 showed onset of tarnishing aftar 3 minutes. Another sample of the Argentium Sterluy alloy that had been annealed in a selectively oxidising atmosphere as disclosed in 'W0 02/09502 showed onset of tarnishing after 6 minutes. The markedly increased delay in Qnset of tarnishing was unexpected in the absence of an 3o increased delay in the case of the standard Sterling Silver article.

- 2'7 -Example 2 Effect o.k post-treataneut saivent cles~~uin~g Example I was xepeated for the Argcntiut~n samples except that instead of buffing witlz cotton wool afCer the mercaptan treatment, the samples were ultrasonically dEgreased in L.nSoIv 765 for 2 minutes. Tl~e samples were then tarnish tested as described ill Example 1 and all fotuid to shnw enhanced tarnish resistance. The ability of the protective effect of the 5teazyl mercaptau treatment tp to survive ultrasonic cleanity in EnSolv suggests that the tarnish resistance is being achieved by a surface reaction involving the stearyl mereaptan and possibly the gcrm~uxium in the Argentium Silver, and not by formation of a grease ox oil layer on the surface of the Ar~entium, l s EaampIe 3 Aqueous dip appiieatian (salvent degreased samples) An anti-tarnish treatment solution was prepared using the followinb 20 ingredients:
Stearyl m~ercaptan 1g EnSuIv 765 5 ml Detergent (Fairy Liquid) 40 ml 25 De-ionised water 100 nil The Stearyl Mezcaptan was dissolved into the )JnSolv 765 after which the resulting solution was mixed with detezgent (Fairy Liquid) and diluted with, eater to provide an aqueous dip. ~ampIes of Argentium silver were polished and ~o ultrasosucally degreased in EnSolv 7bS foz 2 minutes, immersed into the abpve aqueous dip for 2 min~~tes st ambient temperatures and then rinsed under running tap water It was noted the water was irruncdiately xepeiled from the polished surface, which left the samples dty. St~mplcs were tarnish tested as described izi Exarnptc 1 and all showed enhanced tarnish resistance.
s lJxunxplc 4 Aqueous dip application 2 {detergent degreased samples) Samples of Argentium Sterling were degreased in a 2% aqueous salutian IO of a detergent (Fairy Liquid] and were then immersed in the treatu~ent solution of Example 3, Zt was noted that the treated samples had become wt~tez-repellent as descrihed in >rxample 3, Sauzples were tarnish tested as described in ExarnplC

and. all showed enhanced tarnish resistance. The above test was repeated except that the Fairy liquid in the treatment solution was replaced by a liquid hand soap 1s (~0 r<xl). When exposed to ammouum polysulphide solution, the sarxtples did not show enhanced tarnish. resistance, It is passiblc that this nmy have bs;en because the hand soap was snore dilute, zo Example S
Simultaneous degreasing and anti-tarnish t~reatznent The fpllowing solutions were prepared:-25 - 1 gr-arn stearyl mereaptan ~ znl EnSolv 765 20ru1 detezgent (Faizy Liquid) - 100mi de-ionised water ~o ' 1 gram 5tearyl mercaptan - 5 zrzl EnSolv 765 - 30n z1 detergent (Fairy Liquid) - 104m1 de-iaoised water - 1 grant stearyl znercaptan (freferxed quantities) ' S mI Exz$oiv 765 - 40n~3 detergent (Fairy Liduid) - I t)Oml de-ionised water - 1 cram stearyl mercaptan to - 5 m1 hnSolv 765 - 40m1 detergent (p'aixy Liquid) - 500m1 de-ionised water - 1 grain stearyl mercaptar~
is - 5 ml EnSolv 76S
- 40rn1 detergent (Fairy Lirluid) I OOOmI de-ionised water.
The solutions were heated to 50°C in an ultrasonic cleaning tank.
zo Samples zzf polished Argezxtiuzn Silver were ultrasonically degreased in the solutions for Z minutes and were rinsed under rmuzing tap water. For the frst three of the above treatrnent solutions, it was observed ittat water was repelled off of the surface leaving the samples dry. Samples treated with the first three solutions above were tarnish tested as described in Example 1 and all showed 25 enhanced tarnish resistance. Hc~waver, in the case of the samples treated with the last two solutions, water 4vas not repelled off of the surface dttriz~g the rinsing siege. When the samples dried they Showed. streaks on the surface which discoloured dozing the tarnish test. 'fhe sample treated with the SOOml solution showed less di5colouratiozz than the sample treated with the 104Qm1 solution.
The 3o above experiments show that Argentiuzn silver ca~a be simultaneously degreased azzd p:at~;ctcd against tarnish using a thiol treatment ag;.nt applied in an aqueous 3a system, and that the zn,ore concentrated the stcaryl ntercaptanll;nSolv/detergentlWater solution, the better the taznish resistance produced.
s Example G
nirect Appiicatiou - Neat Detergent Solutions (solvent degreased! xcitteatts degreased samples) t o Tlte following solutions were prepared:
- 1 gram stearyl rnercaptali S nil EnSoIv '765 - 40m1 detergent (Fairy Liquid) {Preferred quantities) 1 gram stearyl xnercaptan - 5 ml ErlSolv 7b5 - 40m,1 soap (liquid hand soap) za The stearyl mercaptan was initially dissolved ixito tTie EnSolv, The detergent was then u~ixed into the solutions. Samples of Argetuum Silver were polished and ultrasonically degreased in EnSolv 765 for 2 minutes. Tlie steaiyl ar<ercaptaz~lEnSolv/detergeizt solutior~ were then directly applied to the surface of the Argentitun sammples using damp cotton wool and massaged into lather. T&e samples were then rinsed under running tt~p canter. In each case, it was noted that watex was repelled off of the polished scufsce, leaving the s~nples dry.
Samples were tarnish tested as in >rxample 1 by being exposed to neat ammonium polysnlphide solution over a period of 1 hour. 'They a1I showed enhanced tarnish resistance. The above direct method for applying die Stearyl ~ercaptan was 3o tested on samples degreased in a 2°ro Faity Liquid aqueous solution, Enhanced t<~zush resistance was again achieved.

Example 7 CtQth Application (solvcn# degreased samples}
s Cloths were hrepued by soaking clean cotton cloth in the following solutions:and allowing the cloths to dry D.1 grazxi Stearyl Mereaptarx dissolved in IOOmI ;E;nSolv - 0.~ gram Stearyl Mercaptann dissolved in 100m1 l:nSolv - 1.0 gram Stearyl Mercaptan dissolved in 100m1 EnSolv (Preferred) Samples of Argentiu,m Silver twhich had been polished and ultrasonically degreased in EnSolv 7bS ~ox 2 minutes) were wiped with the cloths then buffed with clean cotton wool. Samples were tarnish tested as described in Example 1 by being exposed to itrnmoniutn polysulphida solution over a period of 1 hour.
All of the samples showed enhan.ecd tarnish resistance.
Example S
~exad~e~yl and aetudecyl morcaptan in ~stiry liguid Hexadecyi rzzexcaptan (ig) in the liquid state was mixed with Fairy liquid tsurfactant containing anionic anal nonionic surface active agents) ~zd with water z~ in the quantities indicated below:
Reforence Fairy liduid (m~} L7~ionised water (mI) 8.1 40 ' Nil 8.2 100 Nil 8.3 200 hril s.-~ ~a loo _ 32 8.5 ~0 244 The ingredients of silulion 8:? appeared to mix well without needing the hekadecyl rn.ercaptart to be dissolved in art organic solvent bcfarehand, A
sample of Argentium silver was immersed in the resulting solution for 10 minutes and rinsed, The swface of the Argentiutn sample had became hydrophobic, suggesting the formation of a layer of hexadecyl mercaptan attaohed to tho surface of the Argentium silver. It rinsed well in water 'vithaue arxy noticeable deposit being lef~C on the surface after rinsing. A region of ih.e sample was rubbed 1 o with cotton wool soaked in EnSolv 765 and then subjected to t~zxtish testing with neat amtnaniurn polysulplSide ovc;r a period of ~5 -minutes. Excellent tarnish resistance was noted, without significant difference between the region that had 'been treated with EnSolv ?6S and the region that had not been so treated.
Similar solutions were prepared from octadecyl mercapf~n and fiairy liquid. Thep were t 5 transparent at first, bztt of lesser stability with separation of a surface layer of octadecyl mercaptan after some months.
example 9 2o Hexadecyl mercaptan in Simply shower gel Hexadecyl mercaptan in the liquid state was mixed with Siwple shower gel (a clear shower gel frartt Aceentia Health and $eauty Ltd, Birminghttrn, UTG, and believed to contain sodium Iaureth sulfate and aoca.midopropyl betaine as 25 principal surfact~rtts, together with cocamide 17EA arid incidental ingredieuts~ arid with water in the quantities indicated below:

Reference HDA~I (g) Simple (ml) Dcionised water (rnl) 9.1 1 100 Nil 9.2 1 100 100 9.3 S 100 100 s 9_4 t X00 100 Shortly after mixing, solutions 9.1 and 9,4 weIe completely transp3ret11 viscous gels free from noticeable separation of the hexadecyl znercaptan.
Sample 9.2 was also Gamgletely transparent but had a water-like consistency and again 14 dad not exhibit sepfuation of hexadecyl ruexGaptan. Sample 9.3 which also had a water-like coz~slsteney appeared as a milky emulsion when shaken but exhibited separation pf hexndecyl mexeaptan at the stud'aee ozz standing.
In a preliminary experiment, a sample of Argentitun silver was immersed n in soiutiou 9.I for 10 minutes and rinsed. The surface of the Argentium sample bad become hydrophobic, suggesCinb the fornxatian of a layer of hexadecyl mcrcaptan attached to the surfaee or the Argentium silver. Xt rinsed web in water without any noticeable deposit being left on the surface after rinsing. lVhen tested with neat amrnoni~um polysulfide, excellent tarnish resistance was noted.
Samples of Argentium silver and conventional Slerlinb silver were prepared-as-follaws. Each scruple was polished with Steelbright polish, followed by raugc, and then ulfrasanically degreased for twa minutes in a 2 vvt% Fairy Liquid solution in water at 54°C. 1t was then further degreased fox 5 minutes in ethanol and immersed at ambient temperatures in the test solulxon. After removal, part of each sample was rubbed ~,vith tissue soaked in BnSolv ?65 and then subjected to tarnish testing with neat ammonium polysulphide aver a period of minutes. Argentium samples showed exeeIlent tarnish resistance and thial bonding, especially good results being obtained with solutions 9.1 and 9.~
~0 compared to the higher water content solutions 9.2 and 9.3, Solutions 9.1 and 9.4 appeared to provide soma tarnish protcctior~ for standard Sterling silver also, but the tluol layer could be removed easily as was apparent from the differences between the entreated and the IJnSolv 7t;5 treated ze~ions.
E~eampla IU
Mixtures df cocamidopropyl betaine (CPR) and sodium l:tureth sulfate (~ST.S) The above tuaterials were supplied as a thick pourable aqueous liquid and as a highly concentrated somewhat gelatinous liquid {7U°lo active) by Surfachern Ltd of T.,~ods, United Kindgom. Hexadeoyl mercaptarc (1 rnl) in the liquid state was mixed with these materials in the quantities indicated below;
Reference SLS {ml) CPB {ml} Water (onl}

10.1 40 40 100 I0.2 40 ?0 100 10.3 30 10 100 10.4 i0 3U 50 10.5 30 10 150 For solution 10. i, Itexadecyl mercaptan was added to a thick mixture of sodium laureth sulphate and cocamidopropyl betaine aver which water was adt~ed and the solution was mixed cold.. 'The resulting mixture initially had a thick foamy-white texture which on settling ttur:.ed into a transparent gel.
Solution I0.2 was somewhat similar. Solution 10.3 was watery and was ioitiaily slightly transparent with lots of bubbles on top ofthe solution., and on sett;ing overnight it became transparent. Solution I0.4 was mixed with gentle heating to about 35°C
Heat appeared to slightly help with the mixing procedure. Atter a few minutes of mixing the mixture foarncd severaly. ~'he mix.-tu.re was allowed to stand overnighf and fUrmed a viscous solution. Solution 10.5 vas heated to appi~oxirnately 35°C
v~hiIst mixing. Water was last in~retiient to be Rdded. Using heat fQr mixing proved beneficial. The solution appeared very foamy but this settled over a few hours (within 12 houzs) to form a transpare»t solution slightly thinker than water.
Argentium silver samples were prepared by polishing iri Steelbright and then rouge, ultrasonically degreasing in a 2°/n aqueous Fairy Liquid.
solution further degxeusing in acetone, immersion in the test solution at ambient tempezatures for i0 mirmtes, and washing under cold rutviing tap water. A
lower rebion of each sample was rubbed with tissue soaked in EnSolv in an attempt to attempt to .remove any thiols, after which the sample was left to stead foz 45 to minutes and wezn then e,cposed to a neat ammonium polysuphide accelerated t~unishing test far 45 tninnutes, Ail the samples showed extremely good hydrophobic properties during the rinsing process which indicates presence of thiols. Water drops were repelled is and throe was no need to dry each sample. The samples performed well in the tarnishing test with resistance to tarnishing and little difference between the rubbed and un-rubbed regions. It was concluded that the hexadanyl meoaptc~n.
in each sample tested had created a tarnish-protective thioi-bonded layer on the since of the Argentium silver.
zo

Claims (23)

1. A method for treating a finished or semi-finished shaped flatware, hollowware or jewellery article of a silver/germanium alloy that has a silver content of at least 77 wt % and a germanium content of between 0.4 and 7% the remainder principally being copper so as to reduce or further reduce tarnishing of the article such that a sample of the alloy of which the article is made can be supported close above a 20% solution of ammonium polysulphide for at least 30 minutes while retaining a generally untarnished appearance, said method comprising surface treating said article with an alkanethiol, alkyl thioglycollate, dialkyl sulfide or dialkyl disulfide

2. The method of claim 1, wherein the alkanethiol, alkyl thiaglycollate, dialkyl sulfide or dialkyl disulfide has C12-C24 alkyl groups.

3. The method of claim 1 or 2, wherein the alkanethiol, alkyl thioglycollate, dialkyl sulfide or dialkyl disulfide is in an organic solvent.

4. The method of claim 3, wherein the solvent containing the alkanethiol, alkyl thioglycollate, dialkyl sulfide or dialkyl disulfide is generally neutral,

5. The method of claim 3 or 4, wherein the alkanethiol, alkyl thioglycollate, dialkyl sulfide or dialkyl disulfide is in a solvent based an n-propyl bromide.

6. The method of claim 3 or 4, wherein the alkanethiol, alkyl thioglycollate, dialkyl sulfide or dialkyl disulfide is in (a) a composition obtainable by dissolving said alkanethiol, alkyl thioglycollate, dialkyl sulfide or dialkyl disulfide in an organic solvent and adding to said solution a relatively concentrated aqueous soap or detergent, or (b) an aqueous dispersion obtainable by dissolving said alkanethiol, alkyl thioglycollate, dialkyl sulfide or dialkyl disulfide in an organic solvent, adding to said solution a relatively concentrated aqueous soap or detergent, and diluting the resulting mixture with water.

7. The method of claim 1 or 2, wherein said alkanethiol, alkyl thioglycollate, dialkyl sulfide or dialkyl disulfide is in a composition obtainable by dissolving said alkanethiol, alkyl thioglycollate, dialkyl sulfide or dialkyl disulfide direct in an aqueous mixture of an anionic surfactant and a neutral, amphoteric or zwitterionic surfactant, said mixture being free from solvents other than water.

8. The method of claim 7, wherein said composition comprises as surfactant a betaine.

9. The method of claim 8, wherein the betaine is cocamidopropyl betaine.

10. The method of any of claims 7-9, further comprising an anionic surfactant.

11. The method of claim 10, wherein the anionic surfactant is of the formula RO-(CH2CH2)n SO3M wherein R represents C10-C18 alky1, n is 2-6 and M
represents a monovalent cation.

12. The method of claim 11, wherein the anionic surfactant is a monovalent cation salt of laureth sulfate.

13. The composition of any of claims 7-12, comprising amphoteric or zwitterionic surfactant and anionic surfactant in a weight ratio of from 1:10 to 10:1.

14. The method of claim 9, wherein the aqueous mixture comprises sodium laureth sulfate and cocamidopropyl betaine.

15. The method of any preceding claim, wherein the alkanethiol or alkylthioglycolate is selected front stearyl mercaptan (octadecyl mercaptan), cetyl mercaptan (hexadecyl mercaptan), stearyl thioglycollate and cetyl thioglycollate.

16. The method of any preceding claim, wherein the alloy consists, apart from impurities and grain refiner, of 92.5-98% silver, 0.3-3% germanium, and 1-7.2%
copper, by weight of the alloy, together with 1-40 ppm boron as gram refiner.

17. The method of claim 16, wherein the ternary alloy consists, apart from impurities and grain refiner, of 92.5-96% silver, 0.5-2% germanium, and 1-7%
copper, by weight of the alloy, together with 1-40 ppm boron as grain refiner.

18. The method of any of claims 1-15, wherein the alloy is a quaternary alloy of silver, copper, zinc and germanium.

19. The method of any preceding claim, comprising the further step of introducing the treated article into packaging.

20. The method of claim 19, wherein said packaging includes a presentation box.

21. The method of claim 20, wherein the packaging includes external.
wrapping for the presentation box.

22. Use of a C12-C24 alkanethiol, alkyl thioglycollate, dialkyl sulfide or dialkyl disulfide in the preparation of a tarnish inhibitor for an article of a silver/germanium alloy that has a silver content of at least 77 wt % and a germanium content of between 0.4 and 7%, the remainder principally being copper, so as to reduce tarnishing of the alloy such that a sample can be supported close above a 20% solution of ammonium polysulphide for at least 30 minutes while retaining a generally untarnished appearance.

23. A finished or semi-finished shaped flatware, hollowware or jewellery article of an alloy of silver containing an amount of germanium that is effective to reduce firestain and/or tarnishing and that has been treated with a C12-C24 alkanethiol, alkyl thioglycollate, dialkyl sulphide or dialkyl disulphide and that exhibits a tarnish resistance such that a sample of the alloy of which the article is made can be supported close above a 20% solution of ammonium polysulphide for at least 30 minutes while retaining a generally untarnished appearance