Clean the sheet of copper. Turn the kiln on to 1,400 degrees F and wait for it to reach that temperature. Put on the gloves, and place the copper on the fork. Use the fork to push the copper into the kiln. Then pull out the fork only. Heat the copper until the surface becomes black. Push the tines of the fork underneath the copper. Then pull it out. Place the copper in a bowl of cold water. After it is cool, move it to a bowl of hydrochloric acid. Scrub with steel wool if any fire scale remains.
Rinse off the acid and dry the copper with a cotton towel. Lay the copper on top of a paper towel. Turn the kiln up to 1,500 degrees. Spray the side of the face-up copper with agar, getting an even coat about the thickness of a fingernail.
Pick up the base enamel color, which you will use for the background of the piece. Hold the mesh screen parallel to the copper sheet, about 1 inch above it. Slowly begin to spoon enamel onto the screen as you move it from left to right in rows. The screen helps to sift the enamel so that you get a more even layer. Stop when the sheet is completely covered with a layer about as thick as a fingernail. Let dry. Spray another layer of agar and recoat.
Put the copper sheet on the fork and place it in the kiln until it glows bright orange, about three minutes. Remove and let cool. Flip the sheet over and scrub with a cotton towel dipped in hydrochloric acid to remove the fire scale from the side that has not been enameled yet. Repeat Step 2 for this side of the sheet.
With colored pencils and paper, draw out the design you would like on the enameled piece. After you've finalized the idea, cut out a stencil, using tissue paper, for each shape you would like to create.
Pick a color to start with. Place the stencil on top of your copper piece and spray it with water until it is damp enough that it doesn't move. Then sift the enamel with the screen to apply it to your piece. Let the stencil dry. Then pull it up, being careful not to disturb the enamel powder you wish to keep. Pour the excess back into the bottle.
Place the copper on the fork and back in the kiln until it glows orange. Remove it and let cool. Repeat Step 6 until you have completed all the colors needed for your design.