If you are printing a double sided board, cover top part of the board (the side with no ink) with black electrical tape to protect it from the acid. Be sure to fold the tape over the edges of the board so no acid gets between the tape and the top layer of the board. If you are printing a single sided board on a double sided copper clad, leave the electrical tape off, the unprinted side will just dissolve.
Put on chemical goggles, latex gloves, and a respirator mask and work in a well ventilated area. Using a disposable, non-metallic measuring cup, measure out 4oz of hydrogen peroxide and pour into a non-metallic disposable container. Using a new disposable, non-metallic measuring cup, measure out 4oz of muriatic acid (you can purchase this at your local pool supply store) and pour into the non-metallic disposable container to mix with the hydrogen peroxide.
Carefully place the copper clad in the acid bath and leave in a well ventilated area for 10 minutes.
After 10 minutes, check to see if the copper has been dissolved. If there is still copper left on the board, use a plastic disposable spoon to gently stir the acid, moving it across the surface of the board. Be extremely careful not to splash the acid. You should be wearing latex gloves, chemical goggles, and a respirator.
Once the copper is completly dissolved, remove the board and dry with paper towels. Rinse with water and dry again. Make sure to store the acid in a properly labeled glass mason jar for reuse on another board.