Technique of coating mirror
The technique of coating mirror was developed by Justus Von Liebig in 1835. Compound of silver and ammonia is poured on the glass surface. A reducing agent like formaldehyde is added to reduce the compound two metallic silver.
The technique of coating mirror was developed by Justus Von Liebig in 1835. Compound of silver and ammonia is poured on the glass surface. A reducing agent like formaldehyde is added to reduce the compound two metallic silver.
To avoid using a chemical reaction, mirror is often placed in sealed chamber which is evacuated. Silver road is heated in the sealed chamber till it evaporates. The silver vapours the mirror slowly. In the same way , mirrors can also be covered with aluminium. Telescope mirror are coated only on the front. Household mirror are coated on the back.
Further, aluminium coating reflects about 92% of blue light and 90% of green and red light striking it. Silver coating reflect 97% of blue light and 99% of green and red light striking it.
Therefore, reflection from aluminium coating are tinted slightly bluish, and reflection from silver coating are tinted slightly reddish.
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