How to Choose Platinum Alloys
What platinum alloys do you recommend for my designs?
950 Platinum Ruthenium
950 Platinum Ruthenium (950PtRu) is the most widely used platinum jewelry alloy in the United States.
- Hardness of 130 Vickers
- Malleable enough for easy setting but strong enough to stand up to daily wear.
- Natural white color is nearly identical to platinum iridium alloys often seen in antique jewelry.
Pro Tip: 950PtRu has a greater tendency to form porosity during casting than most other alloys, but this is easily healed through Hot Isostatic Pressing (HIP).
950 Platinum Cobalt
950 Platinum Cobalt (950PtCo) is unmatched for filling fine cross-sections and design details.
- Greatest molten flow capability of any platinum alloy of the market
- Good hardness of 135 Vickers.
- Its color has a slight blue hue compared to 950PtRu.
Pro Tip: 950PtCo is slightly magnetic and oxidizes when exposed to heat. While this might be troubling on the bench it is often preferred for its ability to cast fine designs and polish more quickly.
950 Platinum Hard Cast
950 Platinum Hard Cast (950PtHCA) is a harder platinum alloy.
- Extra protection against wear and distortion.
- 5% Ruthenium-Gallium offers superior hardness at 180 Vickers.
- It has a natural white color nearly identical to 950PtRu.
Pro Tip: 950PtHCA is excellent for hard-on-jewelry customers who tend to abuse their rings. This alloy has lower molten flow capability so extra care is required in design to fill thin or delicate areas.
Why Not Iridium?
Another commonly asked question is “Why aren’t you casting platinum-iridium?” Widely used for years in both casting and fabrication, 900PtIr and 950PtIr have been demonstrated to be too soft for jewelry applications when used purely in cast form. Both anecdotal and scientific research confirm this fact, so we actively encourage jewelers to switch to one of the above alloys due to their greater wear resistance.
“There is absolutely no difference between working platinum ruthenium and platinum-iridium at the bench” – Experienced bench jeweler and head of TechForm’s wax department, Tim Green. Since joining TechForm, Tim made the switch to 950PtRu for his own jewelry and is very satisfied on all fronts.
For more practical information on platinum jewelry visit Platinum Guild International’s Platinum Resource Center https://www.platinumlearning.com/ .