Some time ago I purchased some 99% IPA from the Chemist – I had to show him my book on cleaning optics before he would sell it to me, for fear of misuse.
I think that anything less than 99% proof “may” be contaminated with other additives. IIRC, one post on sci.astro mentioned that some sort of oil was added to cheaper solutions and this would leave a film after the alcohol had evaporated.
The above comments are made up mostly of memory recollections and is not qualified advice, just a warning to check!
Cheers
Dennis
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