US1947180A - Tarnish resisting silver - Google Patents

Description

Patented Feb. 13, 1934' PATENT OFFICE TARNISH BESISTING SILVER -Blaslus Bart, East Orange, N. 1., assignor to Precious Metals Developing Company, Inc. a

corporation of New Jersey No Drawing. ApplicationJanual-y 21, 1931 Serial No. 510,271

5 Claims. (Cl. 20443) In nw copending application Serial No. 458,906, filed May 31, 1930, I have described a process of producing tarnish-resisting silver, that is, a process for making tarnish-resisting articles including sterling silver and other alloys, silver plate and the like, and particularly such articles as tableware, hollow-ware, prize cups, trophies, medals, jewelry, apparatus and instruments of many kinds, reflectors and so forth. The process as described consists in electro-depositing a coating of rhodium upon the article to be treated.

The present invention relates to a process for the same purpose, one object being to obtain the same or better tarnish-resisting effect at less expense.

Further objects are to provide such a process which shallrequire much less rhodium than the process described in my said copending application; to thus provide. a-process for producing tarnish-resisting metals such as silver, silver compositions or alloys which are normally tarnishable, wherein one or more layers of diiierent tarnish-resisting metals less expensive than rhodiiun are successively applied to the silver or other tarnishable metals to be treated, after which a coating of rhodium is applied, so as to provide the characteristic colorof silver and undiminished or decreased light reflectivity; to provide a process of this character in which the various coatings consist of tamish-resisting metals such as nickel, palladium and rhodium which are applied in the order or their color characteristics, that is, the metal having the color least resembling the color of silver, is appliedjfirst, while the coating having the color nearest to that 01' silver,'is applied last; and to provide such a process wherein a metal, such as nickel, is applied to the silver or other tamishable metal andhas the palladium applied theretoso as to check tarnishing and alloying of the palladium with the silver or other metal and permit a light coating of palladium to be used.

Other objects are to provide a process 01' the character-described, wherein polishing of the various coatings is obviated, it being possible to apply the desired finish to the silver article to be treated, and then apply the tarnish-resisting coatings without further surface-finishing, due

to the preservation of the original finish throughat the various coatings; to provide such a process in which the tarnish-resisting deposit 'or coating is such it cannot be removed by any known method without destroying the article; and to obtain other advantages and results as My process may be and is most usually applied to any silver or silver alloy article or to any article having a silver finish, for example, a solid silver or silver alloy article or an article having the blank or body of base metal and a plating 01 silver thereon.

In carrying out my process, and as one example thereof, I give the article tobe treated an acid bath as is usual preparatory to an electro-deposition process. This acid bath may consist of merely dipping the article in, for example, sulphuric acid,.or the article may be electrolytically treated by using it as a cathodin a bath of from five to ten per cent sulphuric acid solution and with a nickel or lead anode. This electrolytic treatment may be carried onior ten or twenty seconds with a current density 01' from ten to fifty amperes per square foot of cathode surface.

Thereafter a flash coating 0! nickel is applied directly to a silver by any known electro-deposition method. I may use instead of nickel any suitable metal 01' the nickel group such as cobalt or alloys or other metal which is equally white and tarnish-resisting. This process is carried on for a time sufflcient to apply a very light coating or flash of nickel, for example, about two minutes, with a low current density of, for example, from three-tenths to one-half (0.3 to 0.5) amperes per square decimeter of cathode surface. .The nickel coating serves as a check layer to initially resist tarnishing of the silver and to prevent alloying of the silver with the palladium, which is the next coating.

Then the article is given an acid bath to re-, move the nickel electrolyte, for example, in the same manner as first described, after which a flash coating of palladium, platinum or white gold is preferably applied to the nickel coating by any knownelectro-deposition method. This process is carried on for the necessary period 01' time to produce a light coating of palladium, for example, five minutes, with a current density of from 0.2 to 0.3 amperes per square decimeter oi cathode surface. The palladium coating protects the nickel coating and adds to the durability of the article, and more closely simulates the color of silver than does nickel. The palladium coating may be omitted if desired and the rhodium may be deposited directly on the nickel, but the palladium is preferably used because it serves as an additional tarnish-resisting surface and increases the wearing qualities of the surface in addition to its other advantages.

will be brought out by the following description. The article is then given an acid bath to remove the palladium electrolyte and to thoroughly clean the article preparatory to the" application of the last coating.

A coating of rhodium is then applied directly to the palladium or nickel coating, and for this step in the process I prefer to use as the electrodepositing bath or electrolyte, a solution of rhoditun sulphate in dilute sulphuric acid containing approximately two grams of rhodium and 20-40 0. c. of sulphuric acid per litre. The solution is preferably used at a temperature of about eighty to one hundred degres F. with a current density of from two (2) to five (5) amperes per square decimeter of cathode surface and with an inert anode such as platinum. The article is so treated for about three minutes.

As the result of my process, an electro-deposition of the two or three coatings upon the silver or other white metal or alloy is provided, which makes-the metal tarnish-resisting to the extent of being practically non-tarnishing. At the same time, the appearance orcolor or reflectivity of the silver or other metal is preserved to such an extent that the metal treated according to. my invention practically cannot be distinguished from the metal (silver) which has not been so treated. In the case of silver so treated his about twenty per cent whiter than the best tarnish-resisting silver heretofore produced, and its reflectivity or light emcienc'y is correspondingly high, the great improvement is believed to be due to the physical form in which the coatings are deposited. The various coatings are very thin and consequently smooth so as to accurately conform to the surface to which they are applied. For example, if the silver surface is highly polished, this finish is preserved at the end of my process, while if the silver surface is initially given a satin finish, this satin finish will appear in all of the coatings. The rhodium almost exactly corresponds in color to silver and has a whiteness or reflectivity of such degree as to be practically undistinguishable from silver. The first applied coatings of nickel and palladium permit of the use of less rhodium, and consequently reduce theexpense incident to the process below that which would be entailed if rhodium alone were used.

The tarnishresisting coatings adhere very firmly to the base and cannot be removed from the article without completely destroying it, so

that the durability of the article is increased at the same time that the color and light reflecting characteristics of the silver are preserved.

The process is simple and can be carried on commercially without the difiiculties commonly met in other processes ipr the same purpose, and in many other electro-deposition processes, for example, chromium plating processes.

Various changes and modifications can be made, by those skilled in the art of electro-depositing metals, in carrying out my invention, without departing from the spirit or scope of the invention, and therefore, I do not wish to be understood as limiting myself except as required by the following claims when construed in the light of the prior art. The term. silver is used in said claims in the sense set forth at the beginning of this specification, as including sterling silver and other a1- loys, silver plate and the like, and it is not restricted to pure silver or any particular kind of silver except that which is used for its appearance or color or reflectivity or light efiiciency. Variations in the baths or solutions, within chemical or electro-depositing skill, such as in the ingredients or quantities or use of the solutions, are also intended to be within the scope of the claims. Furthermore, while my invention was developed primarily for silver, it can be used for other metals, such as copper; nickel, palladium and many others, including base metals and alloys, such as German silver, which are sometimes used as a. base for such goods as the silver ones herein mentioned.

What is claimed is,

1. An article having a'tarnishable metal body, a coating of a tarnish-resisting, substantially whit metal'over the body metal, and an outer coating of rhodium.

2. A silver article having thereon successive electro-deposited coatings of nickel and rhodium.

3. A silver article having thereon successive electro-deposited coatings of nickel, palladium and rhodium.

4. A silver article having electro-deposited thereon a coating of pmladium beneath which is electro-deposited upon the silver a layer of a me to check alloying with the silver.

5. An article set forth in claim 4, having a layer of rhodium electro-deposited upon the palladium.

BLASIUS BART.