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.

CONS:

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.  

960: A new alloy of sterling PMC

Book made with 960 sterling

For the past year I’ve been working with an enriched version of sterling metal clay. "Enriched" simply means that this alloy has more fine, or pure, silver in it. It's still sterling, and can be legally marked as such.  We're calling it "960". That number refers to the amount of fine silver in the alloy just as 925 identifies regular sterling.  

960 is made by mixing equal parts of PMC Sterling and PMC3. I open a 25 gram pack of PMC3 and a 25 gram pack of PMC Sterling and mix them together. It takes less than 5 minutes. It's really that easy. 

You mix it, kneed it, fold it and so forth until it's uniformly colored.  No water, or oil is necessary when mixing these clays.

This is simple to do because PMC Sterling is a grayish color and PMC3 is more beige. Probably because I've done a lot of cooking in my life, once it’s uniformly colored, I let the mixed clay rest for 1/2 an hour or so.  Enclose it in plastic, the way you would with any other metal clay.

I just taught the first class using this new material.  In the class, at The North Country Studio Workshop conference at Bennington College, the students made their own 960 to work with. It got great reviews.

From left to right: PMC Sterling, 960. PMC3

Although I love the way PMC Sterling handles, it does have a couple of drawbacks, or one major drawback, really; the carbon firing.  Carbon firing is just not fun.  No one likes it and I think it's holding PMC Sterling back from the attention it deserves. It's so much stronger than fine silver PMC, has a longer open working time and superior dry working qualities. But then, you have to fire it, twice, and there's the carbon!

960 is almost as strong (in my opinion), handles almost as well, carves almost as well as 925 PMC Sterling but NO CARBON!  It fires in air on a kiln shelf like any of the fine silver PMCs.  We've been firing 960 at 1500F for one hour.

It has another perk; gold foil, when you keum-boo, goes on more readily than it does on PMC Sterling.  However, it doesn’t diffuse into the silver surface as quickly as it does with fine silver (I guess that’s really two perks).

Is there a reason to continue to have PMC Sterling in my studio?  Yes, PMC Sterling is peerless for that occasional very delicate design that requires extra strength.   It's also, in my opinion, the best way to fire diamonds in metal clay.  Although diamonds will survive an air-fire, the temperature must be quite low or they will not survive.   I like to fire my metal clay as hot as possible so if I want diamonds in a design I will use the original PMC Sterling and I’ll fire in carbon.

How did 960 come about? A year and a half ago I met with Tim McCreight and a few others to discuss PMC Sterling.  On the last day of the meeting we were brainstorming and Tim said, "What if we enriched the PMC Sterling?  By increasing the fine silver content of the alloy maybe we could get rid of the carbon altogether.”

The idea had an immediate effect on me.  It resonated; I went right home and mixed up my first batch of 960 and that's really the only metal clay I've used since then.

Please try it for yourself and let me know how it goes!

Pieces made with 960:

When it's fired and finished, I'll rivet something between the window and the little frame and cover the blank pages with decorative paper.  In air, the pencil burns off.

At this point, after so many 960 pieces, I trust this clay to sinter without distortion, in air, on a kiln shelf.  I'll fire this book soon, but not assembled.  Each page will be laid on the shelf.