Sunday, December 12, 2010

Raku Enamel

I had a student request in my enameling class this semester to see what raku enamel was all about. So in the last couple of classes, we found out! I had done raku in ceramics as an undergrad but I wasn't sure how that translated to enamels. Well, I was surprised to find out the two processes are basically the same. I was lucky to find a section in one of my enameling books, The Art of Fine Enameling by Karen Cohen, on the subject. The article in the book was written by Jean Tudor and I followed her instructions loosely while experimenting/ demonstrating.  This was definitely a learning experience for me as well! Since then I also found an article written by Jean Tudor on Raku Enameling for Glass on Metal. You can also read about Jean's experimentation with raku enamel on her website. The text at each link is basically the same but Jean has some updates at the end of the article.

So here's what I did:
I made two samples- one had a coat of Hard Fusing Clear already on and the other I sifted the green enamel directly on. Jean wrote that the green transparent enamels yielded the strongest results so I just started with them to try and make sure I got some kind of result!

So here are the two examples. On the left is the sample with a clear coat down first and the 4 enamels shown above sifted in a mix. To the right is one coat of the Nile Green over bare copper. You can see how pale the color is. I applied a second heavier coat of these colors to each piece before doing the raku.

The trick to getting the iridescence to come out is to cool the enamel in a reduction atmosphere. So what is a reduction atmosphere? A reduction atmosphere is where the oxygen has been removed. How does one accomplish this? Usually by putting something like newspaper, leaves, sawdust, any organic material that can safely burn, into a container (with a lid), igniting the material then putting the lid on to allow the fire to burn up the oxygen until it burns out and smokes.

Wikipedia explains: "This reduced level of oxygen causes incomplete combustion of the fuel and raises the level of carbon. At high temperatures the carbon will bond with and remove the oxygen in the metal oxides used as colorants in the glazes (enamels in our case but they are both glass). This loss of oxygen results in a change in the color of the glazes because it allows the metals in the glaze to be seen in an unoxidized form."

The green transparents contain the most copper oxides and will do that cool raku thing the best. It is important to get the enamel piece (make sure it is good and hot- do not under fire it in the kiln) into the combustible material as quickly as possible in order that it is hot enough to ignite the material. In order to accomplish this, I have a pair of pliers handy at the kiln and everything set up and ready to go. As soon as I can get the fork out from under the rack when the piece comes out of the kiln, I pick up the pliers, grab the trivet and dump it with the piece face down into the pot with the combustibles.  If something goes wrong and you have to futz with getting it off the trivet,etc. it's usually too cold and the material won't ignite. If this happens, put the piece back in the kiln and try again.

So we are at the kiln ready to go

It's on fire!

Ready to see what we got

It's so incredibly hard to get a good shot of the results because the glass is so shiny, but here we are. On the left- 2 coats of Nile Green over bare copper, no raku. On the right, 2 coats of Nile Green that went through the raku process. You can see a little of the copper on the surface. The Nile Green gave a softer coppery shimmer to the surface.
On the left, 2 coats of the 4 green mix, un-raku'd (sp?). On the right, 2 coats of the 4 green mix after the raku process. This thing is just coppered to within an inch of its life.

 Why is the surface so bumpy, you ask? Because the glass went face down into the combustible material while it was still molten. You can't escape this and if you put the piece back in the kiln to try and smooth it out, you'll lose the iridescence. Think of it as a bonus textural element.

This last piece was pretty darn impressive in terms of the dramatic change in the glass but to my eye, it's just too much. Jean Tudor writes about the judicious use of this technique and I agree. I think this technique will be most effective when used in moderation. But I'm looking forward to adding it to my repertoire to teach and I know I'll continue to experiment- judiciously :-)


  1. Really useful piece, going to try this out tomorrow, thanks :)

  2. Thanks for this! I love the raku texture and shimmer. Great advice here. I will definitely be applying this technique to a few pieces!

  3. I have done some raku enameling in the past. On some of my pieces the color just rubbed off after a while...Have you had this happen ever???
    A. Domash

  4. Hi A. Domash,
    I haven't had the raku rub off but the copper will tarnish and it may appear to rub off since it gets darker. You can try sealing the raku just after you finish it (the surface should be grease free and a semi-gloss spray acrylic will give you the best protection) or you can polish the surface carefully to bring a little copper shine back. It is a thin surface of copper so you do need to be careful not to over polish and never sand it. Just like regular copper, the copper oxides released by the glass will react to the air just like sheet and wire copper. Hope that helps.