Correct Option: D

Glass colouring and colour marking may be obtained by addition of colouring ions, by precipitation of nanometer sized colloides (so-called striking glasses such as “ruby gold” or red “selenium ruby”), by coloured inclusions (as in milk glass and smoked glass), by light scattering (as in phase separated glass), by dichroic coatings , by coloured coatings. Nickel oxide produces deep blue glass.