A student of mine wants to use pennies as part of his surface decoration on a vertical pot along with traditional ^5/^6 glaze. Is this safe for the kiln? Does anyone have experience with this?
Glaze Experiment Using Pennies
Posted 05 March 2014 - 11:31 PM
My only experience left me with a very black thing on the kiln shelf. Penny was put into a pot in the kiln, ended up cracking through the bottom of the pot and turned into a very charred lump. Looked a little like lava.
Now I have to avoid that part of the shelf.
Posted 06 March 2014 - 12:44 AM
Posted 06 March 2014 - 01:05 AM
Posted 06 March 2014 - 09:25 AM
Thank you everyone! Very helpful! We won't be experimenting with this in class as students won't get the colors they were hoping for.
Posted 06 March 2014 - 02:50 PM
I suspect you had a steel core penny and what you saw was a burnt lump of steel. Canada used them from 2002-2012 as well as zinc-cored.
Posted 06 March 2014 - 09:15 PM
Pennies now are not not made of copper. They are a copper plated alloy of mostly zinc. The penny will be long gone before cone 5 as indicated by previous posts. You might pull it off with a real nickel, but most of these ate low melting alloys now also.
Posted 06 March 2014 - 09:35 PM
I feel I should have explained the links I posted further. They contain the composition of US and Canadian pennies throughout history. There are copper pennies in circulation still. You could track them down by the year of minting. Again, I'm sorry for not explaining my links further.
Posted 07 March 2014 - 11:05 AM
Your link was fine Tyler. The point I was trying to make is that neither zinc or copper will not stand up to cone 5 heat for the length of a ceramic firing cycle. Zinc melts and boils away... not good... and copper turns to a lump of black copper oxide during the long oxidation firing. I have tried to re-fire my copper electroplated pots and it was a disaster.
I have not tried nickel. it resists oxidation and has a high melting point. It might be worth a try. If it works, you could plate it with copper if that is the color you want.
Posted 07 March 2014 - 11:19 AM
Ah, I see. I was unclear about the goals of the OP with the pennies. I was thinking that the copper oxide might melt into a glaze for interesting textural and trailing effects.
Posted 07 March 2014 - 11:55 AM
Thanks guys! What about firing to ^06 / ^05 or even ^018? Would zinc or copper hold up better at these temperatures? Just curious if you have tried this.
Posted 07 March 2014 - 12:12 PM
Zinc melts at 419.5 C. I've melted copper in the presence of pyrometric cones and it melts at around cone 1-2 and flows around cone 4. The "bronze" of old pennies might melt at a much lower temperature, though (in around cone 06-04 wouldn't be surprising).
I would try it on a flat tile first to see if the pennies melt, and to see if the CoE makes it even possible. As Colby says, copper inclusions in glass are possible (and common), but they're usually in the form of foil.
Posted 07 March 2014 - 02:25 PM
One thing I have tried that might be worth pursuing... I took very fine copper wire from old transformers. and imbedded it in raku glazes and fired it. The copper didn't completely melt and gave interesting green/reds around the wire after it came out of reduction. My guess is the combination of a fast raku fire cycle, the lower temperature attained, and the large amount of boron in the glaze (80/20 GB/Neph Sy) shielded the wire from oxidizing competently. The down side is that the wire falls off vertical surfaces and it likes to spring out of the glaze. I never tried gluing to the pot first before adding the glaze which might help. This was years ago, and I never did much raku since then. Give it a try and see what you come up with
Posted 07 March 2014 - 07:23 PM
That's a thought Peter. Another thing you could do is use a propane torch to heat the copper pad or copper wire to red heat. This kills the temper and it is much easier to bend and doesn't spring back as much. It get's a black copper oxide layer but you will get that anyway.
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