Glass coloring and color marking may be obtained in several ways. 1. * by the addition of coloring ions, 2. * by precipitation of nanometer-sized colloids (so-called striking glasses such as "gold ruby" or red "selenium ruby"), 3. * by colored inclusions (as in milk glass and smoked glass) 4. * by light scattering (as in phase separated glass) 5. * by dichroic coatings (see dichroic glass), or 6. * by colored coatings