Cool Blue lenses

"Steve B" wrote in news:jp78jk$2om$ snipped-for-privacy@speranza.aioe.org:

Not a good answer but I know that an original pair of Blue lensed RayBan sunglasses will bring mucho-dinaras on the Bay. Whatever mineral that was added to the glass ain't as easy to get as it once was. Think African country.

Probably didymium blue:

from :

Didymium (Greek: twin element) is a mixture of the elements praseodymium and neodymium. Ever since the invention by Sir William Crookes, it is used in safety glasses for glassblowing and blacksmithing, especially when a gas (propane) powered forge is used, where it provides a filter which selectively blocks the yellowish light at 589 nm emitted by the hot sodium in the glass, without having a detrimental effect on general vision, unlike dark welder's glasses. Blocked also is the strong ultraviolet light emitted by the superheated forge gases and insulation lining the forge walls thereby saving the crafters' eyes from serious cumulative damage. (See also arc eye, also known as welder's flash or photokeratitis.)

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Didymium blue filters were once used for OA welding and brazing, but were banned from that use well before the mid 60's when I learned OA, because of inadequate blockage in the IR. While blue looks cool, it is the least useful color for human vision, with the eye having approximately 1% as many blue cones as red and green as well as not properly focusing blue. No way would I consider using an old didymium blue filter for welding, even if it was free. (They are still good for glassblowing, however.)

Regards, Glen