Wednesday, August 12, 2009

Bronz and Copper Clay - Firing Woes

I've got good news, and some bad news. I'll give you the good news first :-)

We are now carrying Bronz Clay, and hopefully we'll have the copper clay soon as well. What I love about the new clays is that they're affordable, and you know me and copper. I can't get quite enough of it :-) The clay retails for $25.00 a pack for 100 grams. If you're accustomed to working with silver- that's 5 times the amount you get in a pack of silver!

This is our Bronz Clay Kit - Sells for $50 - In store only, or feel free to phone or email your order in. I haven't yet got the kits assembled, so if you want one. Please wait for tomorrow as some of the staff may not know about it yet.

The clay alone is $25.00 - in store only - or by email/phone - these are available now :-)

The bad news is that the copper and bronz does need to be kiln fired, and there still appear to be some special considerations you must take. It's also a bit of trial and error. All kilns are different, so you may in fact waste a bit of product while finding the right setting for your particular kiln. I've finally found a successful firing schedule for my particular kiln, and the results are beautiful. however, I've also had some pretty spectacular failures as well.

The bronz and copper both need to be fired surrounded by a coconut carbon. With the bronz, you also have the option of using a coal based carbon which will give you gorgeous rainbow patinas. I've been sticking with the coconut based one for the time being.

One disappointment we've had was the unpredictability of the firing. Sometimes it worked, other times we had to give it a second firing. I 'think' I now have this worked out - but time will tell.

You can get a bronz or copper clay kit, that comes with a pack of clay, some coconut carbon, and a firing chamber. The kit comes with a fairly large chamber, and this was part of the problem for me. Firing is messy, you end of with black soot all over your kiln. I choose to not use our big glass kilns, as then I would have to clean it out all of the time. And it's really hard to sweep out all of that black soot from all of the nooks and cranny's. I used my smaller kiln, that I've reserved for metal clay. Unfortunately, my kiln isn't very tall. The large firing chamber does fit, but it didn't give me very much room around it. This was part of our firing problems.

In order for the metal clays to fire correctly - You need airflow within the kiln. If your firing chamber is too big, there is just not enough room for the hot air to move. Your firing chamber should not be sitting on the kiln floor (use kiln furniture to raise it up at least an inch), and be sure to have at least an inch about the chamber as well. Once we started firing with a smaller stainless container - we had no firing problems at all!

I pulled a batch of copper out of the kiln this morning, and now I've got a batch of bronz firing. I'll pull them out tomorrow and we'll see what we get.

The pics below are copper - This was the third firing of these particular copper pieces. The first go round most of the items crumbled right in the pan. The second firing appeared to do nothing at all. Third time was a charm.

Mona - if you're reading this, I'm sorry about the chip in your dragonfly pendant - but it least it's mostly intact! (Don't worry - Mona knows we were doing experiments!)

This is a pic of the bronz that is now firing in the kiln.



Nathalie Girard - Canadian Rockies Art said...

Wow, thank you very much for mentioning the black soot that you end up with inside the kiln.

I was debating whether or not I should try the Bronze and Copper ones, but I only have 1 kiln and it's for glass and PMC, so the last thing I'd want is have to clean up a mess like that.

You're the first person that I see mentioning this. I haven't read anything about this black soot from anyone else selling these products (I've just started reading up on it recently).

That would be a deterrent for me, unless I had two kilns and one would be dedicated to using these two clays ($$$).


jen said...

It is an issue for sure. Especially if you are doing production glass beads (using your kiln a lot). It IS cleanable (you can take a mini vac to it, but it's still a bit of a pain...

jen said...

I'll take a pic tomorrow, so you can see better what I'm talking about.

jen said...

One day, I'll learn to get all of my thoughts together and post once...

Yes, I think they're not mentioning it, as not exactly a huge selling feature :-) And for those working strictly in metal clay, it's probably not a big deal. Although for glass workers. You're going to want to get every little bit of that black soot out. I haven't tested it of course, but I imagine if you layed your glass bead down on the soot - it would stick to your glass.

Canadian Rockies Art - Nathalie Girard said...

Yes, for sure, if there is soot present in the kiln when firing glass, it's going to end up on it - not good at all :(

And all it takes is one little black speck of soot to ruin a creation made of glass.

I look forward to the picture(s). Many thanks Jen.

Heather said...

Careful too about the any coal left in your kiln. It is difficult to dicern between the coal and the soot. At the Metal Clay conference some people are reporting that coal bits can damage the inside of your kiln especially the muffle fiber type kiln leaving holes, it is unclear as to wether there is the same effect on the kiln brick kilns as the brick are already holey. Vaccum out you kiln after each firing.
As for firing, it is a fiddly thing but air flow is very important as Jen said. I am finding that my Paragon firefly is working pretty well.

A couple other things...sometimes the clay can be bit dry straight out of the problem just with a little time and patience add water to it (this is best done by rolling the clay painting on a layer of water folding, rolling adding water and so on...).

And the last thing sometimes the clay can leave your hands greenish. Gloves in a bottle works wonders for this.

As for the copper it is lovely. I have had some good results. I had had a few brittle pieces but it seems to have occured after I have reheated and then quenched the peices to get a heat patina...I think there is something with the thermal shocking the sintered piece as I refired some piece and they were fine. Hmmmm I will need to test this out more. :)

Heather said...
This comment has been removed by a blog administrator.
Anonymous said...

I just fired my first batch of copper clay. I got the black soot all over my kiln even though the lid was on the stainless steel pan. My stainless steel pan turned black & corroded looking after the first firing. Is this normal? I washed it and it is still black. I did a full ramp to 1650 and held for 3.5 hrs. All my pieces did not sinter well. When I tried to clean them up they broke apart and the steel brush was eating away the insides. I attached copper wire loops to each charm and they are falling off. Where I used past & fresh clay to attach them it is black and just crumbles. This is frustrating. Any advice?

jen said...

Hi Anon,

"I just fired my first batch of copper clay. I got the black soot all over my kiln even though the lid was on the stainless steel pan. My stainless steel pan turned black & corroded looking after the first firing. Is this normal?"

Yes, it is unfortunately. The black will not hurt the pan. It's just what happens when it is exposed to air and hugh heat. All normal. The soot - I still get the soot as well, and just vacuum it out every now and again :-)

" I did a full ramp to 1650 and held for 3.5 hrs. All my pieces did not sinter well. When I tried to clean them up they broke apart and the steel brush was eating away the insides. I attached copper wire loops to each charm and they are falling off. Where I used past & fresh clay to attach them it is black and just crumbles. This is frustrating. Any advice?"

Your firing schedule sounds right. What type of kiln do you have? Also, I need to know what type of media you have in your pan. One of them (the rainbow) cannot be used with copper clay.
Copper wire doesn't work as an imbed. Pure copper wire becomes brittle at that heat and will break unfortunately.
Brass wire should work well - just throw a piece of brass wire in to test it first before imbedding.

let me know about your kiln, and media - I'll see if I can come up with more suggestions for you.

Donovan said...

I am no expert, just learning about the clay myself, but to the person above who is have sinter problems, I would say that your kiln settings doesn't sound fine ... raise the temp somewhere between 1750 & 1800 °F.

Understanding what is happening is important ... sintering is bringing a powder of a material to a point slightly below the melting point of the material, just enough to cause the powder particles to fuse together.

So, it stands to reason then, that if you have powder after firing (and thus, after the binding agent in the clay has been cooked out) ... you didn't have enough heat.

1981.4 °F is the melting point of copper ... so at 1800 you should have enough heat without risking creating a puddle of copper.

Good luck!

Donovan said...

I was thinking more about dynamics with the copper clay, and I guess it is worth mentioning kiln time is probably as important as temp.

Think about cooking a turkey. In a conventional oven, it takes a long time. Getting the correct amount of heat to every molecule on that bird takes time, especially when air is the medium for the heat (ie., unreliable thermo characteristics). That is a large part of why flash frying turkey in hot oil has become all the rage ... oil provides a great mechanism to keep a constant, reliable temperature distributed evenly around your cooking target.

So, I would also say, don't undercut the time ... if the packet says 4 hours ... don't fire for 3.5 hours ... fire for 4. You need time to raise the temp of all of the particles in your medium.

Other notes:

Stainless steel is a generic phrase for one of many different alloys. The blackening might be oxidation or sensitization (chromium carbide formation). Ultimately, it doesn't matter that it is black ... but over time, if it is sensitization that is happening, the stainless steel may corrode and need to be replaced.

Graphite crucibles might be another option, which I think is used when melting copper, a process where stainless steel will corrode after a couple uses.

Soot ... in our kiln, it is just a fine powder at the bottom and easily removed with a vacuum. Probably a result of the clay binder burning out.

Happy cooking!

jen said...

Hi Donovan,

Thank you for your comments. The heat absorption definitely does come into play. I'm still trying to work out the perfect schedule for my particular kiln.
The problems I'm having with my kiln (fairly new Paragon SC2 with bead door) are interesting. 90% of the time, I can fire bronze with no problems at all. It's the other 10%...

I can have two pieces in the kiln, in the firing chamber just under an inch apart. One will sinter (seemingly) correctly, while the other crumbles to dust. Both pieces are of similar size/thickness etc.

I think it's a fabulous product, so I hope no one is taking my posts the wrong way. I absolutely love the bronze clay, and I'm having a huge amount of fun with it. I think it being a new product it will just take a bit of experimentation with finding the right firing schedule for a particular kiln.

Silver firing (whichever brand) has a longer track record of successful firing. I'm sure when it was first introduced (14 - 15 years ago now - correct me if I'm wrong here) there were probably firing issues as those who were using the product got used to it.

As for the dust, yes it does vacuum out no problem, but it doesn't seem to get it ALL out (or mine doesn't comment was just a warning for lampworkers who tend to just toss their beads into the kiln. The beads will pick up any remaining dust. Fortunately, I have a dedicated glass kiln. :-)

The graphite crucible sounds interesting, I'll have to look into that. The stainless does have a fairly short life in the kiln. Mine looking pretty bad, but I have done a large number of firings with it.


Donovan said...

Jen, I think your post is great!

I think it would do the makers of the copper and bronze clays to be a little more informative about these "side effects" of their products and maybe provide some helpful info on mitigating them.

But, since they don't, blogs like yours are exactly how people not only find they are not alone, but what other people have done to mitigate the problems.

I was mostly targeting the anonymous poster above, who was running at 1650 for 3.5 hours and worried about the blackening.

I failed to re-read your response to them before I posted, so I mostly just re-iterated what you said.

Looking around for graphite crucibles in relation to copper smelting has been iffy. There do seem to be two basic kinds, one for below 2000F metals and one for 2750F metals. I would error on caution and try the latter.

As for your 10% bronze, dual result ... very interesting (and problematic!!!) I am no kiln expert ... but it might be interesting to know if it is always the same side of the kiln that sinters consistently.

Anonymous said...

I am having mixed results with firing fastfire bronze clay. I am heating my kiln at full ramp to 1525 and holding for 2 hours as the instructions say. Some of my pieces are coming out fine, others are crumbling and falling apart. I have used coconut carbon with better results than the coal carbon. And it seems the thinner the piece the better it comes out.

My questions is about refiring: Must I refire at the same temp for the same hold time? I'm not sure if I should experiment with changing the temp or the hold, and since I'm new working with bronze, I'm not even sure which would be the best factor to change! I have been working with silver clay and haven't had this kind of trouble before.

I read that it is possible to repair breaks with new clay and refire. Have you had any experience with doing that?

Thanks for being here to field our questions!

Cyndi said...

Hi, I have been working with copper for 3 months now. we have never fired it surrounded by coconut or in a steel container.

We fire it at 1800 degrees for 35 minutes on a shelf. If we have included cubic zurconias, we wrap it in fire paper.

Done this way, you don't end up with any soot or anything like that. We take it out of the kiln at 900 degrees and douse it in plenty of cold water immediately to take the fire scale off (unless there are cubics involved).

jen said...

Hi Cyndi,

Art Clay copper can be fired successfully in the manner you describe. Unfortunately, that method does not work for the other brands of copper clays.

Anonymous said...

The way I deal with the soot is to vacuum in out. Very easy and works perfect.