Fusing Screenprinting with Glass powder - Stylized Flowers
In the design downloads in the appendix you will always find both variants - the background and the motif. So you can make the glasses as positive and negative of the identical design.
In the example, I first sprinkled the clear base glass with white powder. White glass powder looks rather milky as a thin layer. I recommend doing an extensive test series - with different base colors and layer thicknesses. This is the only way to get to know the full range of possibilities.