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.

Click here to see an enameled Art Clay Copper piece.

For the piece pictured in the above link, I fired on five layers of enamel, and flash fired it for a sixth firing.  The enamel held up throughout.   
 
There are two ways to fire the copper clay to ensure success with enamels.   One way is to fire it buried in carbon at 1780F for 3 hours.  This must be done in a BRICK kiln, NOT a ceramic fiber muffle kiln such as a Paragon SC model.   The firing requirements are just too hard on the SC kilns and I did not get a good sintering result with them in any case.

The second method is to open shelf fire the product.  No carbon, no fuss, no mess.  Unlike with the carbon method, this can be done in an SC kiln very successfully.   At this point, this is my prefered method.  It's much faster and easier than messing with the carbon, although it does have it's own quirks.

If you would like to try this yourself, please read on.  PLEASE NOTE:  I still consider this in the "experimental" stage, so be prepared for the unexpected. I'm a long way from gauranteeing results.   In fact, I am anxious to hear how this works for others!  Sometimes what I do in my studio doesn't come out the same when others try it.   I've found troubleshooting problems to be very enlightening.  
 
First and foremost... ALL my test peices are 2mm or less thick.  If you make a thicker piece you may have more problems.   I have not yet had the chance to test thicker pieces, but I know something of what can happen from my experiences with COPPRclay.   A thicker peice can hold more air and more pickle, either of which can destroy your enamels.  Until I test thicker ACC pieces, I can't say what will happen.
 
ACC Firing:

1. Pre-heat kiln to 1780F
2. Fire piece FACE DOWN on fiber paper for 30 minutes
3. Quench in cold water immediately on removing from kiln
4. Pickle to remove remaining fire scale.  This can take anywhere from 15 minutes to an hour.

Preparing piece for enamel

1. Simmer piece in baking soda solution (3 cups water to 1/4 cup baking soda) for five minutes.  I do this on my kitchen stove.  I've been talking to Yolanda Nieuwboer of Holland and she's having success using ammonia instead of baking soda.   Both are base and will neutralize acid, so either should work.   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.
2. 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.
3. 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 tarnish.
4. 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.
5. Dry the piece with a clean paper towel.

Enameling

1. Pre-Heat kiln to 1550F degrees.
2. 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.
3. 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. 
4. 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. 
5. IMPORTANT NOTE:  Unlike sheet copper, Metal clay has air trapped inside that must escape.  The thicker the piece, the more air to be expressed.  The only way for this to happen 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.  Lucky you!  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. 
6. 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.   
7. 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. 
8. 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.

I'll be turning this into a few projects/magazine articles as soon as I do a few more tests.  I'll keep you posted on that.  In the meantime, I have only one thing to ask in return for the above information.  If you try it, let me know how it goes!   Pictures would be helpful too.  Consider yourself an enamel beta tester!   ;o)