Firing & Enameling Art Clay Copper
Aida Chemical has recently introduced Copper Clay to their product line up. Of course for me, the first question was "Can I enamel it?" The answer is yes, but there are some additional steps you need to take to ensure a good result.
Firing Art Clay Copper is easy compared to other brands, although it does have it's own quirks. No carbon, no fuss, no mess. It can be done in an SC kiln very successfully.
The following instructions are a very basic overview of the process. For in-depth instructions, with photographic illustrations, please see my two part article in Metal Clay Artist Magazine, Vol #1, Issue #4 and Vol #2, Issue #1.
FIRING ART CLAY COPPER
- Prepare your kiln by placing four small kiln posts (1" to 2") in the kiln and pre-heating it to 1780F (971C). Put a piece of fiber paper on the fiber kiln shelf, but do not put shelf in at this time.
- Once the kiln has reached 1780F (971C), place the dry Art Clay Copper pieces face down on the fiber paper. Use a pair of very long tweezers or pliers, and a heat glove, to place the entire shelf in the kiln on the kiln posts.
- Fire the pieces for 30 minutes.
- When the firing is complete, use the long tweezers or pliers and the heat glove to remove the shelf from the kiln and very quickly dump the contents off the shelf and into a bucket of cold water. The faster you get the pieces from the kiln to the water, the less fire scale will form.
- After quenching, place the pieces in heated pickle such as Sparex for 15 minutes to an hour depending on how much scale formed. When the black scale has turned to a brownish color, it will brush off easily. Only use copper tongs in your pickle, and rinse your pieces in clean water.
- Use a wire brush with soap and water to brush your pieces.
I fire my pieces face down, because less fire scale forms on the front of the piece that way. I use the fiber paper to prevent the piece from sticking to the kiln shelf. I like to place the pieces on the fiber paper on the kiln shelf outside of the kiln to reduce the amount of time the kiln is open. By having them set up on the shelf and then transferring it into the kiln, you can put all your pieces in at one time very quickly. The kiln posts make it easier to take the shelf in and out. Likewise, I remove all the pieces at one time by taking the whole shelf out and dumping the pieces off into the quenching bucket rather than pulling the pieces out one by one. By doing it this way, you greatly increase the speed with which you get all the pieces quenched. If you take them out one by one, the first piece may not have much fire scale, but by the time you remove the last piece it will have cooled too much and there will be a lot.
PREPARING THE METAL FOR ENAMELING
- Simmer piece in ammonia solution (1 cup water to 1/2 cup ammonia) for five minutes. I do this on my kitchen stove. You can also put the mixture in an ultrasonic cleaner if you have one, rather than simmering on the stove top. I tried the stovetop method to help out the folks who don't have as much equipment and it worked just fine. Rinse well when through.
- Tumble the piece for a minimum of 2 hours. Longer is fine. NOTE that tumbling comes AFTER neutralizing the acid. You want to neutralize the acid while the pores of the metal are fully open. Tumbling burnishes the surface and closes off the pores.
- Clean the piece with either ammonia and a glass brush, or PennyBrite and a glass brush. If you've just taken the piece out of the tumber and it's bright and shiny, you probably don't need to use PennyBrite. Ammonia will work fine to remove any finger oils, dust, soaps or other impurities. If the piece has been sitting around and has darkened, you may need the PennyBrite to clean off the oxidation.
- Rinse Well. After cleaning water should sheet, not bead, on the piece. If the water is beading there are still surface oils. This can inhibit how the enamels adhere to the piece. If you have trouble getting it to sheet, try spitting on the peice and rinsing it again. Spit breaks down just about anything.
- Dry the piece with a clean paper towel.
- Pre-Heat kiln to 1550F degrees.
- Apply counter enamel. I use Thompson Liquid Counter Enamel and oversift it with 80 mesh enamel. Then spray with a light mist of klyr-fire to set it. This will keep it from dropping off when you turn the piece over to work on the front. Set the piece on a trivet to keep from knocking off the counter enamel.
- Front: If you are using transparent enamels, the first layer should be either clear or a very pale color. Medium to dark colors will turn very dark directly on copper. A light flux is needed to start with. I genearlly use 2020 Clear for unleaded enamels, and N1 for leaded. If you are using opaque enamels it doesn't matter so much what you start with. Either sift or wetpack as your application calls for. (for more information on applying enamels, see my book Enameling on Metal Clay.
- Fire the piece for 1.5 to 2 minutes. For this first layer, the enamel not only needs to fully fuse, the copper under the enamel should appear clean and bright. If the copper under the enamel appears dark or reddish, you have not fired it long enough. Eventually, the oxides that make it dark will absorb into the enamel leaving it bright copper color underneath.
- After pulling the piece out, let it cool completely. Clean it with hot water, a toothbrush, and PennyBrite. DO NOT return it to the pickle! It WILL soak in and get under the enamel. And it's not necessary. You can get enough of the firescale off with the PennyBrite, and you avoid the risk of destroying your enamel with the pickle.
- Reduce the temperature of the kiln to 1475F. The high temp is only needed for the first layer of enamel. After that it does better if you working in the more normal firing range for enamels.
- Repeat the enameling steps until you have achieved the effect you were after. Finish as desired. Final bits of firescale can be removed with pickle at this point, but ONLY if the piece is NOT going back into the kiln. The piece can be tumbled to bring the metal up to a shine without harming the enamel.
- You can inhibit the rate of oxidation on exposed portions of the copper by applying a thin coat of Renaissance Wax.
IMPORTANT NOTE: Unlike sheet copper, Metal clay may have air trapped inside that must escape. The thicker the piece, the more air to be expressed. If this happens, it can cause bubbles in your enamel. The only way for the air to be released is through a "gassing out" process. You will see bubbles forming in your enamel and coming to the surface. If you pull the piece out too soon, these bubbles will be trapped in the glass and show up as pits or holes that have to be filled. If you just leave it in the kiln a bit longer (just another 15 or 30 seconds) the bubbles will come to the surface, pop, and the enamel will fill in behind them. Watch the enamel fusing if at all possible and wait until the bubbling seems mostly overwith before pulling the piece. If your enamel fuses completely and does NOT bubble, then you may not have an issue with gassing out on that piece. This process can repeat through the first couple of layers, but should subside on the final layers. Eventually there just isn't that much air still in the metal.