I use the following steps for transparent over white. Please use all safety precautions when working with enamels and torches. These are described in the
basic torch information
After cutting, shaping and punching a hole or holes in my copper piece, I apply and fire two separate coats of counter enamel on the back of the piece. (For further information on counter enameling, please see the above link.)
I usually put the cooled piece in the pickle to help remove the fire scale and oxides on the front of the piece and then rinse off the pickle. (Note: I don't pickle post firing for all opaque colors but find it helpful when using white or other light colored opaques. I simply rinse the piece when using dark colored opaques.)
I sift and fire at least one coat of Foundation White 1030, applying and firing a second coat if I see any metal showing through.
Finally, I sift and fire a coat of transparent enamel over the white. If the color seems insufficient, I may fire additional coats of transparent.
The mesh size of the sifter makes a difference in the color achieved with the transparent enamels. I currently use both an 40-mesh and a 150-mesh sifter in my work. The smaller the mesh, the lighter the coat of enamel delivered to your piece. The 150 mesh which has smaller holes than the 40-mesh does not let the bigger grains of enamel onto the piece. I fired transparent Blue Heron 2650 over white for the pieces below. I used the 40-mesh sifter for the piece on the left and the 150-mesh sifter for the lighter colored piece on the right. You can see some bubble through of the white on the darker piece. This will be discussed later.