Wednesday, November 16, 2011

Testing the new PMC Sterling

I am captivated by the new Sterling PMC; having worked with it since the spring, I want to write a little bit about my experience.

I’m thrilled to be able to say it’s very strong when fired and lovely to work with when fresh. Like PMC Pro, it has a longer open working time than other versions of PMC. When dry, it’s generally similar to dry PMC3 or Plus except it's much easier to carve with gouges. It carves smoothly without chipping, like PMC Pro and like BronzClay.

Sterling PMC needs to be fired in 2 stages, a brief air fire and then a carbon firing. This is more complicated than the needs of fine silver PMC and at first it loomed large as a drawback for me. As I began to appreciate its strong points, however, the double firing became a lot more tolerable.

What follows is a brief story of my experience with the material to date. My plan for the winter is to explore more open work, more ring designs, hollow forms, and larger kiln loads. To be able to rely on metal clay for the kind of strength required by this type of work is thrilling to me. I look forward to developing ideas that I have been reluctant to do in PMC and also reluctant to fabricate in sterling metal.

Five Rings in Sterling PMC:

Please note: The times and temperatures I used in the firings described here were part of my testing process. The times and temperatures described in the PMC Sterling insert are our up-to-date recommendations for firing.

All of these pieces were fired at 1000F for 30 minutes then 1510F for 45 minutes, in well used coal carbon. All were fired with approx. 10mm of carbon on all sides (ie not much carbon).

The first (corset ring, 4 cards thick) was fired flat as a strip then keum-boo-ed on the inside surface with two layers of 24k foil (the gold adhered nicely, although a few tiny spots resisted the bonding). Then the strip was formed into a ring around a mandrel, laced with wire, patinated and polished.

This bee ring was fired face down and in spite of the band being thin, it did not warp or slump. The bee is quite thin, but strong and unmovable with my fingers.

The bee was more challenging to keum-boo than the corset ring, I think because the corset has no texture on the inside.

There was some staining on the surface of the bee that seemed to repel the gold. I tried cleaning it off but I couldn’t get the gold to adhere to some spots. This type of staining, after the carbon firing, has not happened again. The fact that the gold adheres as well as it does to the sterling without depletion gilding or any other preparation is still a mystery.

I made the snake to test a thick piece and to try carving the sterling clay. It is superb to carve.

I made this ring to test strength in open work pieces and also attachments like the little balls, which I attached with slip. It did well on both counts. The ring is thin but strong and the balls are not coming off.

I fired this ring face down in the carbon with a piece of kiln paper under the cutouts and on top of the cutouts so the carbon granules would not jam into the cut out areas. This worked perfectly well although the ring itself is too thin to be practical. In spite of it being thin, it did not slump. I fired this ring with 4 other pieces; two hollow tubes and two flat pieces. All fired to strong metal.

(dry ring)

(ready for firing)

This cylinder is the first hollow form I’ve made in sterling PMC. The caps on the top and bottom are donuts (rather than solid clay). I did this to conserve material. The cylinder did not distort in the firing; next time I will make it thinner walled and lighter weight.

I’m experimenting with firing more pieces in the carbon. The cylinder was fired with 4 other small pieces: 1000F in air for 30 minutes then 1510F in coal carbon for 45 minutes. All pieces are strong and well sintered.

I'll write more as I experiment more and experiment I will. As with the BronzClay, and then the PRO, I look forward to discoveries I'll make bumping along in territory that is not entirely known. As with everything to do with metal clay the pleasure is in the pioneering (well, at least most of the time).

I look forward to hearing about your discoveries, as well!

I'm teaching a PMC Sterling ring class before the PMC Conference this summer. The class is full but please let me know if you'd like to be on my mailing list for upcoming PMC Sterling classes.


  1. Fabulous information Celie! I look forward to trying the sterling.

  2. Celie, after reading your post I am extremely excited about this new material! Thank you so much for sharing in detail the results of your thorough and well-though-out testing. I look forward to hearing more as you continue to explore the opportunities created by PMC Sterling!

  3. Celie, thank you for sharing your excitement and hard work with other pmc enthusiasts like myself who are a little intimidated about trying out the new clays. I hope to learn more about the pmc sterling and get a chance to work with it soon.

  4. what an awesome post! thanks for sharing your experience with this new PMC.

  5. Love that you waited to post after many tests. Your patience is great than mine. : ) Thank you so much for this info. Excited to try it!

  6. Wow, great to hear of your experiments, Celie! I'm very excited about the new sterling clay and look forward to playing with it myself! Thanks for sharing!

  7. Hi Celie, thanks for the info. I may just give it a try. Lovely work as usual. All the best, Hilary Taylor

  8. Celie, thanks for posting this. So excited to try it out!

  9. Very exciting. I can hardly wait! Hope you are well. xoxo~Ann

  10. Hey Celie,

    What a luxury to be able to do so much testing. I was given a small amount of Sterling PMC to test and decided to roll 2, 3, 4, and 5 card thick strips to see how strong they are, and then form them into rings post firing. One ring I put a topper on and refired to test a slip connection post firing. That worked really well, but because I didn't fire in a cage - my band was distorted after firing. I assume by the weight of the carbon. I had almost an inch. You used only 10mm. Interesting. When I get my hands on more Sterling - I'll definitely try your method.

    Thanks so much for sharing your results. I didn't know the class at the Conference was with Sterling! Now I'm even more excited to take it. Huzzah!

  11. Thanks for sharing this... I'm really looking forward to working with PMC Sterling. Love the strength of Pro and how well it carves in greenware, glad to hear the handling is similar - and I guess I can live with the two stage firing process if it frees us to explore more designs that would require greater material strength.

  12. Hi Celie,
    Thank you so much for sharing this....and am I glad that I am doing your class at the PMC con - can't wait! I'm only just beginning to play with all these clays so I have an exciting journey ahead of me!

  13. Hi Celie ~

    Thanks so much for your post! I'm beyond excited for this new material - what was the shrink rate for it? I can't seem to find that info anywhere!

    Thank you!
    ~ Ana

  14. Thanks for all your kind words! Having a lot of fun experimenting and I look forward to hearing how the sterling works for you!

  15. What an interesting new material. Thanks for this info Celie. When I heard about this new PMC, your blog is the first place I came to learn about it, and this was so helpful. Look forward to more info, thank you! Riki

  16. Thanks for shareing your tests, I have been trying it out myself and really pleased with the results so far,It take a bit of getting use to the flexibility at plaster dry stage, thats a bit weired, but lovin being able to make big stuff like bangles and cuffs, so looking forward to doing your class at the conference

  17. Thanks Riki! Tracey - I'm looking forward to seeing you in class and seeing what you've done with PMC sterling!

  18. I'm very appreciative for the posts!
    I wanted to make more rings, but wasn't happy with the PMC for durability.
    I will order some today....
    you've given me the courage to "go for it".

  19. I would like to make and fire a sterling cup. Should carbon be allowed to fill the interior, or should the inside be screened off in some way? Also, should cork clay be used on the inside of the cup during the initial firing to prevent slumping, and will it burn off completely during that firing? Thanks for your thoughts on handling a larger hollow form of this kind.

  20. Hi A, The answer partly depends on how big your vessel is. When I made the little tall box pictured on my home page I put a square of kiln shelf paper over it so carbon would not get in (I felt there was some risk of distortion from carbon in the interior of the box). Then I surrounded it with carbon.
    I don't have much experience with cork clay as a support material. I prefer to build the piece so it is sturdy enough to support itself and so far, that's worked out okay.
    As I said, a lot depends on the size of your piece. In general, when starting with a new material I like to start small then work larger as I gain confidence. Perhaps you did this?
    Best, Celie

    1. Loved the tutorial here. Would love to do a class too. Can the pmc sterling be fired in coconut carbon as the copper and bronze clays or is it a whole other kind?

  21. Hi Anon,
    Absolutely, PMC Sterling must be fired in carbon.
    I use the following firing schedule: Fire pieces in air, on a kiln shelf at 800F ramp to 1000F, hold for 45 min. Cool, then transfer pieces carefully to a steel container in which you have put 10mm of activated coco carbon (same stuff you use for bronze clay). Cover the pieces with another 10mm of coco carbon, cover the container and fire again: full ramp to 1500F, hold for 1 hour. Cool until it's safe to handle then remove your pieces.
    Glad you like the blog, thank you. My class 2013 home studio class schedule will go up on my web site soon.
    Best, Celie