Platinum Guru

Before platinum can be used in jewelry making, it has to be alloyed to create the metal most suitable for a specific application. Platinum can be alloyed with a multitude of metals to create a harder, more usable alloy. Platinum alloys range in purity from Pt 950 to Pt 900 and Pt 850. Pt950 contains 950 parts per 1000 of platinum and 50 parts per 1000 of another metal. Pt900 contains 900 parts per 1000 and 100 parts of one or more other metals. Pt 850 is not very common and is usually found in chain product.

Alloying platinum with different metals creates a variety of properties that make platinum extremely versatile. Adding five per cent ruthenium creates an alloy suitable for machining and faceting on a lathe. Many wedding bands are made this way. A five per cent addition of cobalt to platinum creates a very fine casting alloy. This alloy is hard and strong, yet very fluid and capable of filling very fine detail during the casting process. Adding tungsten will create a springy alloy that is generally used for findings. There are many more specialty alloys on the market, not to mention proprietary alloys that manufacturers create to make jewellery such as tension rings.

  ~Jurgen

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One of the finest 950 platinum casting alloys is platinum 950/cobalt 50, also known as 95/5 cobalt.  This alloy has a very fine grain, high liquidity, and the ability to fill intricate detail.  With a hardness of 135 HV and the ability to cast well and take a good polish, it is one of the most popular casting alloys in Europe and the

.  Platinum 950/cobalt 50 is also slightly ferro-magnetic, making identification easy (you can simply use a magnet to detect attraction).

This alloy does oxidize, however.  Because of this tendency, propane and other fuels do not work well with it.  Instead, torch melting should be done with a hydrogen/ oxygen fuel mix, which does not permit much oxidation.  This alloy is most successfully cast with induction heating in a controlled atmosphere.

  ~Jurgen

For torch casting, the most commonly used platinum casting alloy is platinum 900/iridium 100.  This alloy, also referred to as 90/10 iridium, has good working characteristics, casts well, can be welded, and does not oxidize.  It also offers a bright white color and has sufficient hardness at 120 Vickers (HV).  It was the universal platinum alloy in the

for many years.

In recent years, many casters have begun using a platinum 950/iridium 50 alloy, known as 95/5 iridium, to comply with the 950 standard.  (Many countries, including the

, require any item stamped “platinum” to be at least 95 percent pure platinum.)  Unfortunately, this alloy is not a good choice for casting.  While it has great characteristics for fabricating, including rapid work-hardening, as cast it has a hardness of only 80 HV-far too soft for jewelry.  (A minimum hardness of 120 HV is recommended.)  With wear, rings bend and scratch, and stones come loose.

  ~Jurgen

Fusing a platinum seam is preferable over soldering and should be done when possible.  However, there are different alloys used in platinum and these should NEVER be mixed.  Only fuse Iridium Platinum with Iridium Platinum.  Only fuse Cobalt Platinum with Cobalt Platinum.  Only fuse Ruthenium Platinum with Ruthenium Platinum.  Never mix them, if you are not sure of the alloy content, use solder.  Platinum S+ can not be fused.  You must use solder when working with it.

~ Brad

Platinum Jewelry,Fabrication,Casting

The FTC Platinum Guide for marking jewelry made wholly, or in part, of platinum provides that items consisting of:

*  950 parts or more per thousand of pure platinum can be marked "Platinum" without the use of any qualifying statements;

*  850 to 950 parts per thousand can be marked in accordance with international standards of "950 Plat." or "950 Pt.," "900 Plat." or "900 Pt.,"

*  "850 Plat." or "850 Pt.”  (The revised guide permits the use of a two or four letter abbreviation for platinum);

*  500 parts per thousand of pure platinum and at least 950 parts per thousand platinum group metals can be marked with the parts per thousand of pure platinum, followed by the parts per thousand of each platinum group metal (example: "600Plat.350Irid." or "600Pt.350Ir.” and less than 500 parts per thousand pure platinum cannot be marked with the word platinum or any abbreviation thereof.

Copies of the Platinum Guide Federal Register notice and the entire Jewelry Guides are available from the FTC’s web site at http://www.ftc.gov and also from the FTC’s Public reference Branch, Room 130, 6th Street and Pennsylvania Avenue, N.W. Washington D.C. 20580; (202) 326-2222

Jurgen

Platinum in its pure form is very soft and needs to be alloyed.  These Platinum alloys have different advantages and are used for specific purposes.  The flow properties of the 950/50 Platinum /Cobalt mixtures are best suited for casting.  With this alloy, very fine pieces of excellent quality can be cast, and considerable detail can be achieved.  Pt/Co has an annealed hardness (HV) of 130 and when cold-worked achieves a hardness (HV) of 270.  It polishes well and holds its luster for a long time.  When welded with a torch Pt/Co may oxidize slightly.  This can be removed by firecoating the object after the initial welding and re-heating it to about 1000° F. Pickle in a 10% solution of nitric acid.  The oxidation will not reappear during wear.  It is not possible to torch-weld different Pt alloys together as they have different melting points.  It is always safe to solder them together using 1500 or 1700 solder.  As a point of interest, Pt/Co is slightly magnetic.

Be sure to wear #5 or #6 welding goggles to protect your eyes.

Platinum /Cobalt alloy is slightly ferro-magnetic.  This Pt950 alloy has very good flow characteristics and is a superior platinum casting alloy.  With its good hardness, it takes on a great polish.  The best way to size a Platinum /Cobalt alloy ring is soldering with 1700 solder.  Roll the solder paper-thin, wedge it into a very well fitting seam and heat.  The seam should be very, very thin.  Now use a file to remove excess solder, and BURNISH the seam with a Tungsten burnisher.  This should remove all traces of the seam.  Now polish and clean the ring.

Jurgen