…if you ain’t got that “plink!” Some bronze and copper clay pieces came out of the kiln fully sintered and some didn’t. Yet they all were fired at the same time. I haven’t done this enough to keep track of where I’ve placed pieces in the kiln to see if that is relevant to which ones sinter and which ones don’t. But, after firing, I have started dropping each piece, from about 2 feet high, onto a table to see if they make that metallic “plink” sound. The pieces that hit with a dull plunk have most likely not sintered properly. These I will tuck in the stainless steel box with my next batch to fire, and I’m pretty sure they will sinter properly when fired again. So far, I can’t tell the difference visually. The earring on the left, below, broke easily when I started to bend it a little. You can see the crumbly brown interior of an unsintered piece of base metal clay. The one on the right made a better sound, and did not start to break, but I will still refire it.
The pieces below seemed to be fine, by the sound of my “drop test.” However, when I polished them with a Scotchbrite wheel, the copper earrings on the top left clearly had not sintered properly.
Come to think of it, the copper earrings above made more of a “thuddy plink” when I dropped them. I though they sounded metallic enough, but it was still a little different than the others. I’ll have to learn to tune my ears to these new bronze and copper clay sounds.
Below are 3 sets of earring components, made with a mix of copper and bronze clay, polished. It’s hard to see the difference between the two metals without applying Baldwin’s Patina to darken the copper. (They all passed the “plink” test!)
Barbara S Fernald Jewelry 
Hi, there, I admit I lurk on your blog ;-0 But I can’t fire at all bronze and copper together. If I fire high enough to get the copper to sinter, the bronze blisters. But the other thing I’ve noted is that with both bronze and copper, but copper in particular, if there is the slightest bit of contaminant in the layers of the clay or if I haven’t gotten the moisture perfectly distributed, I get pitting and spalling, like your 3rd photo. I’ve also got incomplete sintering like you show when I’ve overworked the material. I suspect that introduces contaminants. My best results have been with working the material in plastic wrap and touching it as little as possible. So maybe this is more comment than necessary from a relative novice. But I do really enjoy your work! Cheers, LeAnn
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Hi LeAnn,
I always appreciate comments. I think especially with the copper and bronze clays we are all novices, and any comments or questions help us with figuring this out.
The weird thing for me is that some of the combined pieces sintered just fine and some didn’t. The copper pieces that started to crumble when I was polishing them with a Scotchbrite wheel, were in the same batch as the mixed pieces. I’ve been using Hadar Jacobson’s powdered clay and firing schedule. (If you haven’t looked at her blog, you really must!! Her work is amazing!! I have a link to it on this site.) But I only had my kiln go up to 1530ºF for the second firing, and hold for 3 hours. I think next time I’ll try a full ramp to 1550º for 3 1/2 hours and see what happens.
I’m curious. Which clay are you working with?
I have not tried Rio’s copper clay and only tried their bronze once. Hadar’s is so much cleaner, but it does need to be worked more to get the binder particles to dissolve so they don’t leave pits.
Ha ha! now you have probably heard way more than is necessary from this relative novice!
xo Barb
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Hi, again. I’ve been using Rio’s clay, mostly because I am lazy. I too love Hadar’s work and she gives out fabulous information. The Rio bronze is a lot more crumbly than the copper which is very smooth. The Rio copper goes to 1650 to sinter. I think maybe I’ll stick in a copper piece in my next bronze 1550 firing to see what happens. I hold for 2 hours on both bronze and copper and get good sintering. I tumble all of my pieces after wire brushing, again a lazy factor here on finishing. I come at all of this from a ceramics background and have never used fine silver clay. So my whole understanding of the firing process is probably a little weird and the working of the raw material is a challange as it is not like clay at all. I’ll check back with you again! And thanks so much for the details. LeAnn
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hmmm…
so much to think about!
contaminants? overworking? i am at the stage where i probably will just focus on fine silver because honestly i, too, have a bit of the lazy in me….all the problems with bronze i’ve had aren’t really worth it since i don’t love the way my bronze turns out….silver is easier and i can get it to do EXACTLY, predictably what i want…and i only wear silver, also….
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Hi Holly,
I hear you about the bronze clay. But I love all of the work you’ve done with bronze clay and pearls on your Etsy page. (hkellogg.etsy.com)
I also really love the feeling of going back to silver clay after trying to make the bronze and copper work out.
LeAnn – You’ve never tried silver PMC? I bet you would really like it. So much easier than bronze and copper. The firing is so much more predictable, and you don’t have to use any activated charcoal. If you try it, be sure to save all unfired scraps. Unlike the base metal clays, oxidation is not an issue. The scraps can be ground up and rehydrated.
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