Measure about one tablespoon of black paint powder onto the center of your palette, With the edge of the palette knife, break up any clumps in the pigments. Grind the paint with the flat side of the palette knife until it feels and sounds smooth. Then mound the prepared powdered paint into a pile. Using the blade of the knife, pat the paint flat to about 1/8" thickness.
Then using the end of the palette knife, take some powdered gum arabic and, gently tapping the knife, sprinkle the gum over the surface of the paint. Use only enough to give the impression of a faint dusting of snow or sprinkling of salt. This step is crucial to the end result, as too much gum arabic makes removal of the paint from the glass with brushes and sticks difficult. Too much gum arabic can also cause the paint to bubble and splatter at firing temperatures. The correct amount may require some trial and error, but it is better to have less than more gum arabic.
Blend the gum and paint together while dry. When thoroughly mixed, push into a mound, and make a valley in the center. Add about 1/2 teaspoon of water and with your palette knife, blend the pigment with the water. Add water and continue to blend until the paint is silky smooth and the consistency of thin yoghurt. Work the paint with a circular motion across the palette, then repeatedly "pile" the paint to the center of the palette.