Platinum Alloys: Features & Benefits
This presentation is designed to familiarize you with the assorted platinum alloys that are available in the industry today. Once you know the features and benefits of each alloy, choosing one that will be suitable for your manufacturing venture will be less difficult.
As most all platinum alloys can be used for casting, it is important to find the one that will be the best suited on many levels. The alloy should be fluid, it should be filling fine detail and should be hard and scratch resistant. A Platinum / Copper alloy for example, may be good for fabricating and forging, but it is not the best choice for casting. The alloy will tend to be porous, have a high non-fill rate and will often require re-working.
The issue of hardness, scratch resistance and denting can be an important consideration when casting is the manufacturing method. Most castings are cleaned and polished and there are no other steps taken to work-harden the metal. Thus the “as cast” hardness of the alloy becomes an important consideration. Alloys such as Platinum/Iridium 950 have a very low hardness and thus are not recommended for casting. The same can be said for many Platinum/Palladium alloys that are used mainly in Japan. These alloys have a very low hardness as well as a grayish color. Many Japanese manufacturers are rhodium plating their product to achieve the whiter color as well as a harder skin on the jewelry. In the States, jewelry manufacturers are often creating platinum jewelry that is of mainstream design and was originally created to be made of a different metal, and not necessarily of platinum.
This can lead to problems down the road, as structural issues, design features and finishing procedures will need to be addressed. Some alloys will be more suitable to different manufacturing methods. This will be an important factor in the selection of the alloy.
The usual manufacturing methods are casting, stamping, machining and hand fabrication. There are other, not so common manufacturing methods, such as electro-forming and just recently, powder technology has entered the field. Today, however, we are looking at the major manufacturing methods and the alloys suitable for them. Hallmarking and purity issues are also a consideration, as many markets have zero tolerance for purity. (This is compared with gold, where the tolerance in the U.S. is 3 parts per 1000 for the actual alloy and 7 parts per 1000 for solder seams.)
To guarantee that the platinum will pass assay, the alloys that are made by metal providers such as Johnson Matthey, Engelhard-CLAL, C. Hafn er and such, are usually better than the stamp indicates. A Pt950 alloy for example will actually be made of 952 parts of platinum. The Platinum/Copper alloy used in Germany is even better as it has 960 parts per 1000 of platinum. Jewelry made of 952 alloys will have no problem passing assay.
The problem with assaying issues will most likely come from the manufacturers who are choosing to alloy their own and do not sweeten the alloy with the extra 2 /1000 platinum in order to get a small price advantage. This is too close to the purity limit and will often create a problem. As soldering is done and components are attached, it is possible that these items will not pass assay. As you know many platinum solders do not contain too much platinum and thus can lower the purity of the piece.
This can lead to a much greater expense than the extra 2 parts per 1000 would have been in the long run. Another point to consider is the expertise that metal providers have to do the alloying. Many manufacturers who attempt to melt sponge and metal grain together will experience a large learning curve and expenses. Alloying platinum is not as simple as alloying other precious metals. Platinum can be easily contaminated and then the loss can be substantial.
In this paper, I will discuss the most common platinum alloys in detail and talk about some not so common ones in general. Even though there are a few platinum alloys of lower purity, I will focus on platinum alloys with a minimum purity of 850 parts per 1000 of platinum. The main focus being 950 parts per 1000 alloys. Here I want to mention briefly that there are also micro alloyed, very high purity alloys used in Japan and Germany, with a purity of 999 parts per 1000. If you need technical information on these alloys, your metal provider will be able to provide that. You may also get the information through Platinum Guild International and I will provide an e-mail address at the end of this talk.
Platinum 850/150 Iridium is used in Japan for watch backs and spring application. It is stamped Pt850 and is sometimes also seen for chain product. It cannot be hallmarked in the UK.
Pure platinum has a hardness of 40 HV. Adding iridium to platinum has an immediate effect on hardness. Even small quantities will harden platinum.
The above mentioned alloy has a hardness of 160 HV and is therefore suitable for special applications.
Because of its hardness it can be machined and will be used for watch backs. It polishes easier than the 900/Ir and 950/Ir alloys. Because of the high cost of iridium, it is an expensive alloy to make. New heat treatable alloys have been developed to create spring and hard cases for watches without compromising platinum purity or hallmarking. The melting range is 1800-1820C, ductility (Elongation) 15% and the specific gravity is 21.5.
Platinum 900/100 Iridium has been used in the United States and other countries for a long time. It used to be called Indio/Platinum and would be stamped IRIDPLAT in the U.S. Today it is stamped 900Pt, 900 Plat or Pt900. It is an excellent general purpose alloy.
Bright, white color, excellent all purpose alloy. Does not oxidize and thus can be welded as well as soldered. Seams will stay bright and shiny after welding.
While it is not suitable for hallmarking in the U.K., 90/10 Pt/Iridium enjoys a great popularity in the U.S. as an all purpose alloy. The color is bright white, it work hardens rapidly and can be cast, machined, and used for fabrication. The melting range is 1780-180013C and the specific gravity is 21.5. Ductility is 20%.
This alloy contains 902 parts per 1000 platinum and 98 parts Iridium. The hardness is 110 HV.
Platinum Iridium 950 is used in the U.S., Germany and Japan. It is a very good alloy for hand fabrication. Because of its low hardness, 80 HV, it is not really too suitable for casting. Cast pieces will scratch rapidly and tend to deform. Cast prongs can be easily bent and thus can loosen stones in the settings.
Bright white color, good ductility. This alloy work hardens rapidly to over 140 HV and is thus good for hand fabrication, die striking/stamping. It can be welded and soldered without any problem.
Excellent for hand fabrication, forging and custom assembly, this alloy is a favorite of the bench jeweler. It can be hallmarked internationally and is usually available as wire, sheet, tubing and casting grain. The melting range is 1780-179013C, ductility 30% and specific gravity of 21.45. The high ductility makes it ideal for die striking or any operation that requires forming, stretching and such. Welding seams remain bright and shiny. Because of its softness, polishing takes some extra effort.
Platinum 950/Ruthenium is used in the U.S.A., Hong Kong and Europe. It is a good alloy for machining and has found wide acceptance in the manufacturing of wedding bands. Typically, Pt950/Ru is made into tubing, which is then sliced and turned into wedding bands. It is also an excellent general purpose alloy and is used for custom fabrication as well. Die striking is also a manufacturing method for which Pt950/Ru is suited well. It can be hallmarked internationally.
Pt950/Ru has a good white color. Jewelers prefer this alloy because of its hardness and ease of fabrication. Casting is a little more difficult and often fine detail will not fill. Because of the relative low price of ruthenium vs. other PGM’s, some casters in the U.S. have switched to this alloy.
Pt950/Ru is the most commonly used machining alloy in the States. It is mainly used for wedding bands and other jewelry requiring lathe or machining. It has a high ductility and therefore is also used for platinum wire and chain making. The melting range is 1780-17951)C, ductility is 34% and the specific gravity is 20.7.
Platinum alloys containing palladium have traditionally been the alloys of choice in Japan.
Generally Platinum/Palladium alloys are very soft. To create a Pt/Palladium alloy that will be harder and thus more versatile, JM created the next two Pt/Pd/Co alloys especially for the Asian market. 850/Cobalt50/Palladium100 is a Japanese alloy and is used to create very hard castings. This alloy is not available in other countries.
The addition of cobalt hardens Pt/Pd alloys considerably. This alloy has a hardness of 150 HV as cast and is used to create very hard castings.
High hardness, good casting properties. The melting range is 1710-17301C, ductility of 22% and a specific gravity of 19.9. This alloy cannot be hallmarked in the UK.
Platinum 900/30 Cobalt/70 Palladium was created to give a mid range hardness to a palladium alloy. It is available in Japan.
This alloy has a hardness as cast of 120 HV and is used for medium hard castings.
High hardness, good casting characteristics. The melting range is 1730-1740C. Ductility is 22% and the specific gravity is 20.4. This alloy cannot be hallmarked in the UK.
In my research for this paper, I found that, while the above alloys are casting alloys used in Japan, the most popular Japanese casting alloys are still the Pt/Pd alloys I will introduce in a moment.
For chain making, many Japanese Manufacturers use Pt850, a combination of 850 Platinum with palladium and copper. Some manufacturers are using 8% Palladium and 7% Copper, others are using 10% Palladium and 5% Copper.
For chain making it is usually 90%Platinum and 10% Palladium.
Some manufacturers are preferring 900 Platinum with 50 Palladium and 50 Copper.
For chain making the favorite combination in Japan is 95% Platinum and 5% Palladium. Some chains are made from the Platinum 95%/5% Copper alloy, and one manufacturer is using Pt95%, 1% Ruthenium and 4% Palladium.
This is a very soft platinum alloy used in Japan, Hong Kong and to a lesser extent in Europe. It is used for casting all, including delicate settings.
Melting range: 1755-1765°C.
Hardness: 60 HV (annealed) and 68 HV (as-cast).
Specific gravity: 19.8.
This is the preferred general purpose alloy in Japan. It is used for soft castings, intricate settings, and fabrication. Used in Japan and Hong Kong.
Soft and ductile, which minimizes tool wear.
Melting range: 1740-1755°C.
Hardness: 80 HV (annealed) and 72 HV (as-cast).
Specific gravity: 19.8.
It has a dull gray color and is soft, so most manufacturers Rh-plate the Pt jewelry. Inferior for machining and grinding, does not have a good, shiny finish. Unsuitable for cutting and polishing as it has low ductility, low hardness, and low tensile strength.
This is the third of the palladium alloys that are used in Japan. It is mostly used for chain making.
Melting range: 1730-1750°C.
Hardness: 90 HV (annealed) and 64 HV (as-cast).
Specific gravity: 19.1.
If you wonder why the Japanese jewelry industry is set on using palladium alloys, so there is a historical reason. Traditionally Japanese craftsmen have gotten used to palladium alloys. All machines and equipment are adjusted to these alloys. To change this would add more cost to recycling charges, which would make the jewelry less competitive. There are no plans to change to a different alloy system for the time being.
Platinum 950/Cobalt is the undisputedly best alloy for platinum casting. It is very strong and has excellent casting properties. With this alloy it is possible to cast pieces of considerable detail and finesse. It is also used for chains, where a strong and thin wire is required.
Platinum 950/Co is slightly ferro-magnetic. It also does oxidize at about 100013C with a grayish/bluish oxidation. It is somewhat difficult to weld with a torch, but no problem to solder with platinum solders. It is being used all over the world for casting. Can be hallmarked internationally.
Pt950/Co has a high hardness of 135 HV. It is very fluid and has a fine grain structure which makes it the ideal casting alloy. Some bench jewelers still resist the fact that some special steps are required to weld/solder with this alloy, but the benefits by far outweigh this minor inconvenience.
Pt950/Co has a melting range of 1750-1765C, ductility 20% and specific gravity of 20.8.
This platinum alloy is mainly used in Germany, some other European countries and Hong Kong. It is a general purpose alloy and is mainly used for fabrication.
Pt960/Cu is flexible and can be welded and soldered. It has been the general alloy of choice in the German market for many years. It is not recommended for casting, as it tends to oxidize a little during the melting and it is difficult to fill fine detail.
Pt960/Cu is inexpensive if you compare it with platinum alloys that are using PGM’s for alloying. It has large universal appeal, a good color and work-hardens well.
Melting range: 1725-1745°C.
Hardness: 120 HV (annealed) and 108 HV (as-cast).
Specific gravity: 20.0.
This alloy was developed by Engelhard-CLAL to create an alloy with the fluidity of cobalt and the flexibility of copper.
This alloy is very fluid and has a hardness of 120 HV. It is not ferro-magnetic and does oxidize at 1000°C as does Pt/Co.
Pt950/Co/Cu is a versatile alloy for casting, forming and machining applications. It has a good color and can be welded and soldered.
Melting range: 1750-1760°C.
Hardness: 120 HV.
Specific gravity: 20.1.
In this section I would like to discuss alloys that are being created for specialty purposes. Among these are the heat treatable platinum alloys of late. There are several proprietary alloys on the market and the inventors do not disclose the contents of the alloy.
Most metal vendors carry at least one of these alloys. Usually they are based on gallium/indium combinations. It is important to remember that these alloys have a lower melting point than regular platinum alloys. Usually a platinum alloy will melt in the mid to high 1700°C range. These specialty alloys will melt as low as 1500°C.
This alloy is hard, springy and can be cast. It is used for findings and other applications where springiness is needed.
an entire new spectrum of possibilities. Made into tubing, these alloys can be machined with very little tool wear and because of their strength a thinner, lighter piece can be manufactured without sacrificing durability.
Earring nuts will not loosen, The jewelry does not scratch as easy as other, softer alloys. The alloy can be soldered and welded without losing its characteristic. Solution heat treating will produce hardness above 200 HV (1000°C 1 hr/quench).
Aged at 600°C for 1 hr will bring the hardness up to 300-350 HV.
Melting range: 1550-1625°C.
Hardness: 200 HV (annealed) and 340/360 HV aged.
Specific gravity: 20.22.
Platinum /Tungsten is an alloy that is not made for casting. It has high springiness and is used in places where a spring action is required. It differs from the gallium systems, which can be cast and have a much lower melting point.
Available as wire or sheet, this alloy is very hard and springy.
This alloy can be welded and soldered to create springy appliances on jewelry. A tongue of a bracelet lock, for example. It has a good color and polishes well.
In this presentation I attempted to provide you with information on platinum alloys to help you make an informed decision as to which alloy to employ for your manufacturing venture. There are several alloys I did not mention, mainly because they are experimental and have not found their way into the mainstream.
An alloy is chosen for its capability, ease of recycling and many other criteria. It must be user friendly, scratch and bend resistant and hold your stones securely. It is further of importance that it can be finished with few or no problems and hold a shine. These alloys that can do all this are here. They are on the market and can do just what you are looking for. It is sometimes just a matter of breaking old habits to see a major improvement in your product.
Just as casting technology has come a long way from the vertical torch casting machine to the high tech pressure/vacuum machine, so have platinum alloys.
Platinum is the most precious metal in the world, a metal worthy of being called precious.
Source: By Jurgen J. Maerz, Platinum Guild International, 2004