Which of the following imparts a deep blue color to glass?
(1) Cobalt oxide
(2) Cupric oxide
(3) Ferrous oxide
(4) Nickel oxide
Answer: (4) Glass coloring and color marking may be obtained by addition of coloring ions, by precipitation of nanometer-sized colloids (so-called striking glasses such as “ruby gold” or red “selenium ruby”), by colored inclusions (as in milk glass and smoked glass), by light scattering (as in phase-separated glass), by dichroic coatings, by colored coatings. Nickel oxide produces deep blue glass.
