Cause and remedy of rainbow color defect on sheet glass?

Answer 1

The rainbow colour is caused by either dispersion within the glass or by interference. If dispersion, the glass, as noted above, has internal strains that cause a variation in the refractive index. Annealing the glass in a kiln could relieve the strain. If the cause is diffraction from a surface film (also noted above) the solution is to clean the glass. If you need a very clean surface, use a drop of acetone on lens paper. Draw the paper across the surface such that a solvent front moves with the paper. Discard the paper and repeat until clean. For stubborn organic contamination, an oxygen plasma furnace is very effective. A riskier strategy is to use a dilute solution of HF to etch the surface layer of the glass (and any contaminant).

Answer 2

Cause is a film or strain that causes a difference in the speed of light through the glass. (index of refraction differences)

Remedy is to replace the glass.

Answer 3

Usually, the cause is a thin layer of oil or a residue of cleaning (!) solutions. Probably the best way to fix it is to wash it once again with a couple of drops of the "streak-free" solution used in dishwashers. It's a pure detergent, with no solid residue.

Rinse. Rinse. Rinse.

Squeegee and set aside.

Answer 4

the remedy should be washing glass with Chromic acid....nothing cleans glass like chromic acid. (its pot.dichromate+dil sulph. acid/HCl+lots of water)

But take care since it's really itchy can burn your clothes.

Search wikipedia for more.