. Frost ball using very fine silica dioxide (cabosil) mixed in a varnish binder.
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Gently sandblast inside of ball with very fine abrasive.
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Sand inside of ball with #600 wet silicon carbide sandpaper (tedious)
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Find can of translucent spray privacy paint jar or translucent paint at art store.
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Find Jewler's Rouge or Lapidary Abrasive and scratch inside of dome. Opticians that actually make eye glasses, may have the abrasives.
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Water Glass, (Sodium Silicate in water used for preserving eggs) mixed with fine white sand
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Varnish mixed with fine white sand.
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Worse case, find a glass installer or university chemist and ask them to Frost ball in very weak Hydrofluoric Acid (HF ) etching crème (Note HF is very dangerous, corrodes your nearest bones to dust if you get it on your skin, must use heavy rubber gloves and safety glasses )
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A very serious car parts place might have the abrasive for lapping valve seats.
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All of the above are what I can think of that will do this. I don't know if any of them are available in your area.
Steve
Qui habet Christos, habet Vitam!
I should have rented the space under my name for advertising.
When I still could have...