You limit your options when you say you don't want to use any harmful chemicals! Nevertheless, you might be able to use silver leaf for gilding.
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Well, you could suspend the glass in a vacuum, vaporize silver (usually with an electric current) and electrostaticly deposit the vapor on the glass.
You could paint the glass with silver paint, or aluminum paint.
Hard to give options when you haven't said what it's for, or what the tolerances are, or if it has to be silver or if it has to be glass.