All Stabilio pencils are perfect for marking on glass because the marks easily wipe off glass. Whether you use them to drawing a design on the back side of a glass item you want to mosaic (DO NOT DRAW ON THE SIDE YOU WILL MOSAIC ON) or simply to mark how you want to cut and individual piece of glass to fit into a mosaic, these pencils do the trick! These pencils sharpen to a fine point using a regular pencil sharpener! Buy either separately or in a set of two-black and white.