A New Silver Alloy by Celie Fago
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.
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.
At this point, after so many 960 pieces, I trust this clay to sinter without distortion, in air, on a kiln shelf. Please try it for yourself and let me know how it goes!
960 Silver Ring Test by Lora Hart
I'll let you in on a little secret. I don't always practice what I
preach! Sometimes I try things that my better judgement knows may not
work. It's a function of my excitement when trying a new technique or
creating a special design, my experienced ego thinking that I have
magical skills that can produce anything in any way, and plain old
laziness. For instance, last week I made a ring using the newly
discovered alloy of sterling and fine silver that Celie Fago is calling
For those who may not be Facebook users, or who may not have read of this new discovery on Celie Fago's blog - the .960 alloy is a combination of equal parts PMC3 and .925 clay. Mix it yourself,
let it rest for about a half hour, and make your creations. Then fire
on an open shelf. No carbon required! You can read more about it
I didn't have any PMC3, so I used PMC+. Old, dry PMC+. And the sterling
clay wasn't that new either. And I didn't wait 30 minutes after mixing
for the alloy to blend and condition. And, since I was in too much of a
rush to make .960 slip, I tried joining elements with PMC3 slip, or the
water/squidge method. (Do you know that method? Brush water on both
elements, let it soak in, add a bit more water, and then move the parts
back and forth against each other a bit to stir up some slip [squidge],
hold for 4-5 seconds and hope for the best. It's a real technique.
I fired at the recommended schedule of a fast ramp to 1500ºF, for an
hour, on an open shelf. The ring band seemed like it was sintered, and
it was strong when pressed between my fingers. But, when I started to
polish it with my motor tool, the decorative elements started to pop
off! Dang! Perhaps the user error was that I didn't join well enough, or
perhaps it was the materials I used. Maybe PMC3 slip and the
water/squidge system weren't good choices. Perhaps I was just in too
much of a rush. I also wondered if it had anything, at all, to do with
the fact that I speed-dried my work on a coffee cup warmer.
because I'm teaching a ring class with this new blend, and want my
students to work with the best material possible, I ordered some PMC3
and a new package of .925 clay and made the new alloy again. To make
samples for the first week of my class, I made three flat strips
(decorated with scratch foam textures) that I planned on bending after
firing during class. I fired at the recommended schedule again. But when
I started to do the demo for my students and bent the strips into
bypass rings (with fingers touching, slowly and methodically) - SNAP!
The first one broke into three pieces. I tried again with another strip
and as I moved from one end of the strip to another - SNAP/CRACK! It
broke again. Sigh. This time I wondered if the different
thicknesses/uneven topography of the scratch foam texture made it
untextured, 4 card thick, .960 strips made with
PMC+ bent perfectly. But then I remembered that .960 is NOT fine silver.
It's a sterling alloy and it might have needed to be annealed. Sterling
actually heat hardens at around 500ºF so it might have even hardened
while slowly cooling in the kiln overnight. For those of us used to
working with fine silver - we have so much to keep in mind now with all
the different alloys. And it seems right that an acute bend - like in a
ring - would need annealing. A more gentle bend - as in a cuff bracelet -
Tip of the Day: You can tell if sterling
is annealed by marking it up with Sharpie ink - when you've played the
flame over the metal until the Sharpie burns off - it's annealed. That's
the easy way. The 'right' way is to coat the metal with flux, then when
the flux gets glassy - it's annealed. Easy or 'right', it's a good
trick to know. You can also anneal in a kiln by taking the temp to
1000ºF for about 30 minutes, and quenching immediately.
The next day, I decided to do some tests. The right way. Like I should
have done to begin with. I assumed that my firing schedule must have
been off for MY particular kiln, so I lowered the ramp to 1500ºF per
hour and fired at 1520ºF for 1.5 hours. I made round coil bands, round
flat bands, washer rings, and fired another flat bypass strip at the new
schedule. I was so excited to test my results. But when I tried to bend
the strip, POP! It snapped again! Double Dang! The band portion of the
strip bent beautifully, but when I got to the center signet I had
incorporated into the design, the band broke off. I wondered if the
signet was making the forming difficult, so I decided to make one last
simple ring strip. Success! Fired for an hour and a half at the schedule
above - it, and all of my student's rings, bent beautifully. Annealing
and a steel ring mandrel helped form the last half inch of each side of
the strip into a perfect circle.
At the risk of treading on our Technical Advisor, Janet Alexander's
toes, I'll share my findings in the hopes that they will help when you
make rings with the .960 alloy.
Ring 1 had prongs that broke off while polishing.
You can see the settings I created to fit the prongs into. I thought they were well attached.
Ring 2 broke when I tried to make the acute bend with my fingers.
Ring 3 bent perfectly. It started 3"long/4 cards thick, shrunk to 2.5" and bent to size 7.
Each commercial ring sizing system is slightly different and measures slightly different sizes. For instance, my steel ring mandrel registers sizes slightly larger than my aluminum multi mandrels. The wooden multi mandrels are probably yet another measurement. Metal, round ring sizers come up with a different diameter than the blue, plastic ring sizers.
And those white plastic 'zip tie' style sizers wind up at still another
measurement. U.S. sizing measurements are different from Euro
measurements. The only way to find and make consistent sizes is to use
the same tool for all measurements.
• All test items were produced with a consideration towards structure, but not design.
• Minimal sanding/clean-up/refining was performed.
• In my opinion, 4 cards thick (wet) is too thin for washer and flat
(meant to be bent to size post firing) rings, even with the stronger
alloy. I suggest 5 for flat rings and 8 for washer styles.
• 4 cards thick seems perfectly fine for round, band rings.
• The 4 card thick washers were easily distorted, although I did not try to actually bend them in half.
• All rings were fired without the use of a ring core.
• A ring core/plug will stop a ring from shrinking past the desired size, while it continues to shrink in thickness and height.
• Ring sizes are in U.S. measurements
• YOUR RESULTS MAY VARY
Washer rings (4 cards thick): approx. 20% shrinkage - I suggest
sizing up at least 3 - 3.5 sizes if using a firing plug, 4 sizes if
firing without a plug.
Size 8 wet - 7 dry - 3 3/4, 4 fired
Size 9 wet - 8 dry, 4.5 - 4 3/4 fired
Size 10 wet - 9 dry - 5 fired
Flat Band and Coil rings were left to dry on ring mandrels, so there are no wet to dry measurements.
Flat Band rings (5 cards thick, 1/4" wide):15% shrinkage
Size 8 pre-fire - 5 fired
Size 9 pre-fire - 6 fired
Size 10 pre-fire - 6.5 fired
Coil rings (rolled to a calibrated 8 cards/thick) - 11 gauge after drying/12.5 gauge after firing:
Size 8 pre-fire - 4.75 fired
Size 9 pre-fire - 5.5 fired
Size 10 pre-fire - 6.5 fired
Flat, untextured strips (4 cards thick): 15% shrinkage
2"/50.8mm dry - 1 11/16"/43mm fired
2.5"/63.5mm dry - 2 1/8"/54mm fired
3"/76.2 mm dry - 2 9/16"/65mm fired
3.5"/88.9 mm dry - 3"/75.5 mm fired
All in all, I like this new alloy. It seems stronger than fine silver
and can be open fired on a shelf. Easy peasey! The round rings, both
flat band and coil band, seemed much stronger than fine silver - but
could be distorted into an oval shape with my fingers before polishing. I
didn't try to distort with tools - any ring made of any material,
whether milled metal or metal clay, platinum, gold, or silver - can be
bent and broken when mishandled or manipulated with tools. Rings I later
polished were plenty strong and could not be reshaped by hand. Although
I did end up having success with this style perhaps adjustable rings
that will be fired flat and bent to size after firing are better left to
.925 sterling. Maybe more testing should be done with textures other
than scratch foam.
To help with the figures used for this post, this site and this site had some wonderful ring sizing charts, and this one helped me to figure out shrinkage percentages. Note that the ring size numbers differ from site to site!
Used with permission
Lora Hart / PMC Connection
NOTE: The mixture of PMC Sterling + PMC3 is stronger than the mixture that uses PMC+. Read all of the data and articles on both product pages
and choose your desired formulation or give them both a try. You can
find more great information on the new 960 and other metal clay intel
from Celie at: www.celiefagojewelry.blogspot.com