114 - The Way to Tint Glass Balls, and
Others Vessels of Clear Glass, From the Inside, In All Kinds of Colors, So They Will Imitate Natural Stones
Have a ball of glass, or else glass of another shape, that is clear and beautiful. Take isinglass [fish glue], that has been infused in common water for 2 days. Put this hydrated isinglass into a bowl of clear water, and boil it until it all thoroughly softens. Make sure there is enough water to make the glue quite soft, and then remove it from the fire.
When it is lukewarm put some in the glass ball, and swirl it around well. Turn the vessel, and in this manner bathe the entire inside of the glass with the glue. Then pour out the excess. Drain it and have the following colours ground and ready. Start with minium [red lead], pour it inside the ball of glass, sprinkling the colour so that it runs in waves. Use a small spoon made of reed to cast the minium in more areas.
Next, throw in the blue enamel. Sprinkle it with the reed spoon forming waves [of color] within the ball. In turn do the same with well ground [green] verdigris, then with [yellow] orpiment also well ground, then with lake well ground.
Always for each color, throw it in waves, in new areas. By means of the glue, which will bathe the paste within, all these colored powders will adhere to the glass.
Now take well ground plaster of Paris, put some into the glass, and quickly turn it all about, so that it will adhere to the
entire glass from within [backing the colors]. Do this operation quickly while the moisture of the glue is fresh, therefore the powders will adhere well Empty the excess plaster inside through the hole in the ball. It will appear tinted in various colors in a most beautiful sight, which resembles natural hard stone toy amusements.
In the end, when the glue is fully dry, these colors affix themselves [to the glass] so they will never come loose. From the outside, the colors will always be beautiful. Affix these
balls to wooden bases, or other painted materials, and keep them for their beauty on study shelves, and on desks, where they make a very beautiful sight.