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 here.
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. Honest!)
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.
Then, 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 unstable. Flat, 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 - might not.
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.
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.
My next experiments will be with container forms and flat pendants. I'm looking forward to it! If you've used .960 we'd love to know about your experience! Please leave a comment here or write a post on our Facebook page.
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!