Bronze & copper metal clay not firing properly...:(

[Sage]

Hi I made some small test pieces of copper clay (Creative brand) and fired them according to the manufacturers instructions (covered with kiln blanket and fired at 920C for 30 mins, then put in picklean for 10 mins) and they came out beautifully. But when I then fired some pendant shapes they turned black as soon as they were out of the kiln and were brittle and all broke apart after I took them out of the picklean. I tried again this time using the Bronze clay, and the same thing has happened:'(

I'm not sure what's going wrong, considering the first batch were fine, and I'm using a brand new kiln (Paragon SC2). The only difference I can think of is that the test pieces were thicker - my pendant shapes were about 1.5mm thick.

Does anyone have any advice they could share, or insights as to what is happening. I'm afraid to fire any more unless more gets ruined...

[caroleallen]

I'm not sure anyone on here uses copper or bronze clay but you never know. Sorry I can't help.

[MeadMoon]

I've not used Bronze clay, but the only time I tried Copper clay the same thing happened: the first batch worked fine but all the others were too brittle and fell apart. My thoughts were that the clay deteriorates (oxidises?) very quickly once the pack has been opened so you might have to use it all at once.

[bronzepaul]

Hi I made some small test pieces of copper clay (Creative brand) and fired them according to the manufacturers instructions (covered with kiln blanket and fired at 920C for 30 mins, then put in picklean for 10 mins) and they came out beautifully. But when I then fired some pendant shapes they turned black as soon as they were out of the kiln and were brittle and all broke apart after I took them out of the picklean. I tried again this time using the Bronze clay, and the same thing has happened:'(

I'm not sure what's going wrong, considering the first batch were fine, and I'm using a brand new kiln (Paragon SC2). The only difference I can think of is that the test pieces were thicker - my pendant shapes were about 1.5mm thick.

Does anyone have any advice they could share, or insights as to what is happening. I'm afraid to fire any more unless more gets ruined...

I have the same result - black and brittle. How do I speak to the manufacturers? This clay is so easy to use - not requiring carbon for firing. Must I go the route of messy dusty carbon?

[camalidesign]

Copper and bronze clay (and sterling silver clay too) has to be fired inside a stainless steel container with carbon covering the pieces. Take a look at this, read the info saying copper and bronze clay can only be fired this way: http://www.metalclay.co.uk/products/Stainless-Steel-Firing-Pan-%252d-SC2.html

I also always fire at the optimal time (3 hours for silver at 900 degrees and if I remember rightly, hours for bronze as well), not the shortest. With pieces as thick as 1.5mm I would definitely fire for longer, they clearly haven't sintered and so are not yet a properly "formed" metal, still just metal particles in binder hence breaking as soon as you handle them. Have a read of this for firing bronze, probably a similar article for copper there too: http://www.cooltools.us/BRONZclay-Firing-s/1211.htm

Hope this helps!

EDIT: Oops, just realised you said this was clay from Creative, which ovbiously have different instsrcutions, not come across them before. Fact still remains that I do think they need firing for longer being quite thick.

Carin

[t1ggerk1ns]

You said your test pieces were thicker than the pendants, so maybe they were fired for a little too long? I don't have a kiln so all my pieces are torch fired and I have found that as with baking cakes, the time varies for size and thickness.

[camalidesign]

If they are brittle and break that means they haven't been fired for long enough, the metal hasn't fully sintered yet.