Tuesday, February 25, 2014

An Experiment; 960 made from PMC Sterling and PMC Plus

So many of you have asked if you could mix PMC Plus with PMC Sterling to get the mixture we’re calling “960” that I decided to try it.  I’ve resisted doing this because although I (hugely) prefer Plus to PMC3 for its working qualities, if I’m trying to make the strongest mixture I can that does not require a carbon fire, it’s logical to use the strongest fine silver clay; PMC3.  But since you’ve asked, and since I really do like the qualities Plus brings to the table, I went ahead and tried it.

I weighed out and mixed equal amounts of PMC Plus and PMC Sterling to make the alloy I'll refer to as +960, and let it rest for ½ an hour.  I decided to remake these earrings (pictured above); Each earring consists of three textured parts, two thick ones (5 cards) and a very thin one (2 cards).  I rolled the 5’s this thick so I could carve them when dry.  I made the striped ones two cards to test strength, both the strength of the dry clay and the strength of the fired metal.

Once fired, I Keum-boo-ed the thinner components. A simple (and unscientific) bend test suggested they were stronger than if I’d made them from PMC Plus or PMC3 alone but not quite as strong as if I’d made them from 960, the PMC3/PMC Sterling mix, which I will refer to as 3/960

Pros and Cons:

PROS of the PMC Plus and PMC Sterling mixture (+960)
•Much less sticky than PMC3 alone or 3/960 (made with PMC3 and PMC Sterling).
•Takes texture better than PMC3 or 3/960 because it’s less sticky and has less “bounce back”.
•The mixture has a longer working time than PMC Plus alone.
• Better dry-working qualities than Plus alone. It’s more elastic than PMC Plus. This +960 carves beautifully when dry, just like the original 3/960. The kind of carving I did on these earrings wouldn’t have been possible on pieces made of PMC Plus alone as it’s too brittle.
•When fired, this mixture takes keum-boo gold readily.  In that respect it is comparable to 3/960.
• It patinas as well as 3/960 made with PMC3 and PMC Sterling.

There is only one con as far as I can tell (after this very limited bit of research):  960 made with Plus is simply not as strong as 960 made with PMC3.  


  1. Celie, thanks for doing this testing. I always appreciate a good experiment.

  2. Celie, thanks so much for doing this experiment and sharing your results! The 960 formula is a groundbreaking discovery and knowing that it's possible to use PMC+ for the fine silver half of the mixture, and the pros and cons of doing so vs. using PMC3, is great. You continue to be innovative, scientific and generous with your experiments and the entire MC community thanks you!

  3. Thanks Celie for doing this testing and filling us in on the pros and cons. Thanks again.

  4. Thanks for the info and testing your the best!!!

  5. so, how does "not as strong" manifest itself? easily bent, not good for a shank, or ..... I'd be interested to know. But I will make some tests too. good to know about keum boo. thanks Celie--the testing Queen!

  6. Thanks for your comments!
    Barbara, I did a very small narrow experiment, just to get an idea of what this mix would be like. I would characterize the difference between Plus960 and 3-960 as similar to the difference between PMC Plus and PMC 3. The 3 is just that little bit stronger. But, yes, you should try it!

  7. Celie - You are the best! Thanks for experimenting, testing, and publishing your findings. This opens up a ton of possibilities.

  8. I was almost giving up on metal clay and your experiment has turned me around. Thank you, Celie!

    1. Don't give up, Cristina; this is great stuff!
      You are welcome!

  9. I have been playing with a mixture of PMC3 and Sterling 2/3 to 1/3 and I find it is really great for molding and seems to take a mirror shine much better than either clay when used alone. I do have to hold the high temp ( I use the recommended temp for the fine silver and add 100 degrees) and slow ramp and hold for 30 mins. I fire mine in ceramic paper envelopes and do not use carbon.

  10. Do you need a kiln to fire the 960 or can u torch fire it?