Why Use Platinum-Cobalt Alloy?

By Stuller | August 15, 2012

Change is never easy. You invest a lot of time and energy learning how to do something, and then there is a change that means you have to learn a new way of doing it.

Some of you have commented on our change from Platinum-Iridium casting alloy to a Platinum-Cobalt alloy, because it means you’ve had to learn a new set of procedures in working with the metal. However, if you look at the changes you have to make in your techniques, it is less of a transition than the move from gold alloys to platinum. And, when you factor in the benefits that this Platinum-Cobalt alloy offers, you come out ahead in learning this new set of skills.

For example, this Pt-Co alloy was developed more than 20 years ago and has been used extensively in Europe and Japan for jewelry. It’s not new, and it was developed specifically to perform better in jewelry casting than either Platinum-Iridium (Pt-Ir) or Platinum-Ruthenium (Pt-Ru).

If you look at a cross-section of cast pieces, you will see that the Pt-Ir and Pt-Ru always show more porosity than the Pt-Co alloy. That means you get the benefit of a denser, more solid casting without the problems that porosity can create.

The as-cast surface of Pt-Ir and Pt-Ru is always much rougher. Because of the smoother surface, Pt-Co requires less finishing, resulting in a higher finished weight and less metal loss both of which keep the manufacturing cost down.

And since Pt-Co has a better fluidity than Pt-Ir or Pt-Ru, you get a better fill rate and a much higher yield in the casting process, once again enhancing the manufacturing process and reducing manufacturing cost.

Working with Pt-Co at the bench requires only a couple of changes from your Pt-Ir techniques-

  • Don’t use boric as a firecoat during soldering. However, you can clean up any surface discoloration that occurs during the soldering process. Be aware that the heating temperature for this clean up is 1200 degrees Fahrenheit, not Celsius.
  • Since the cobalt is very slightly magnetic, you need to be careful about contamination with bench scrap. However, since all platinum alloys are very easily contaminated, you shouldn’t have a problem if you follow good housekeeping procedures.
  • Although you can’t weld Pt-Co alloy to Pt-Ir alloy, you can easily weld it to itself. Stuller offers both sizing stocks and solders for Pt-Co applications.

Probably one of the most useful things about the alloy is that it can ethically and legally be marked as Platinum without having to list the alloy component, since it is 950 pure. That’s not the case with Pt-Ir, which is only 900 pure Platinum.

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8/23/2019 Market Prices:
Gold 1503.80 Platinum 865.00 Silver 17.05