Multiple choice

Deep blue colour is imparted to glass by the presence of _____.

  1. Iron oxide

  2. Cupric oxide

  3. Nickel oxide

  4. Cobalt oxide
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Cobalt oxide (CoO or Co3O4) imparts a deep blue colour to glass when added in small amounts. This 'cobalt blue' glass has been used since ancient times. Iron oxide gives green/brown colours, cupric oxide produces blue-green, and nickel oxide can produce brown or violet colours depending on concentration.

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