Originally posted by lmd91343 I wish to remove the coatings from a Pentax A 50mm f2.0. Are all the elements glass?
Yes, but there are different types of glass used in this lens.
Originally posted by lmd91343 I would use steel wool to remove the coatings. Obviously, steel wool should not be used on plastic.
For the love of god, do not do this. Crown glasses used in older lenses contain lead which make the glass somewhat softer and easier to shape, this property is why lead crystal glass is commonly used for ornate glassware. Some of the elements in the 50mm f/2.0 have high concentrations of lead in them and would be quite easy to damage them with steel wool. Personally If I wanted to remove the coatings from a lens I would strip it down clean the lens elements sonically and place the elements in an acid bath to remove the coatings and re-polish the elements with a suitable polishing compound afterward, ferric oxide would be an effective (albeit messy) way of doing it.
Originally posted by lmd91343 Glass is harder that steel. Glass is more brittle, but harder. In a previous life I cleaned VERY expensive, custom blown lab glass with steel wool.
Lab glassware is constructed to high standards using tempered borosilicate glass that is harder than steel and less prone to fracture under temperate extremes and is resistant to abrasion. I have used fuming aqua regia to clean glassware without the surface getting etched but the materials are far from indestructible - Frisky perchlorates if mishandled, can pulverize lab glass back into sand in a fraction of a second.