White spots explained

[lucamax]

White spots are due to a small part of resin that do not polymerize in a continuous film but leaves a surface with holes and gaps where air appears that  change the refractive index of the surface.

This is why these spots appear white but if you wet them with a solvent they temporarly disappear.

The main reason is the presence of water or cleaning solvent with water inside as Alcool not  99,9%   water remains trapped and leads to impefections in the film of the polymer surface.

A solvent with a very  rapid evaporation rate tends to enhance the phenomenon even without water or humidity presents.

[cliffyk]

Great explanation!

With this "COVID" nonsense I am lucky to be able to get 70% IPA "rubbing alcohol". I had been using Klean-Strip's ≈50/50 methanol/ethanol "stove fuel", however I find that Lowes, Home Depot and Ace Hardware no longer stock it, A lawyer friend told me he had seen in a trade rag that there were liability concerns because assholes were using it as a personal and evironmental "sanitizer" (Methanol will kill you).

The water content of the rubbing alcohol is a problem--I have been using a cheap hair dryer (SWMBO wouldn't let me use hers) to dry everything completely before it goes into the curing chamber.

Not perfect but seems to be an OK¹ solution...

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¹- Those who know me understand that when I say "OK" I mean "barely acceptable". Often my wife has to interpret this and other stuff to family members and friends, such as when I say "I don't care." what I mean is "I don't care." (as in I REALLY don't give a crap)

It is not some snotty "OK, whatever" response as it seems to be with many.