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[Orchid} Infrared light

         At risk of straying outside my sphere of knowledge...
This sounds to me like a bit of cross-communication. I use shade 5
goggles for welding (oxy-acet.), and the fact is, they are not so
dark that you can't see your work piece, though visibility is not
great. They are not like the shade used for arc welding, where you
can't see a thing. So, gold coating or not, if the green
polycarbonate is shade 5, then that's that, gold or no. If, on the
other hand, more light comes through these gold glasses than an
established, certified  shade 5 filter, then it's not OK, and
that, also, is that. Right? 

Noel, I have to agree. I also use shade 5 filters for welding and
also when doing extended periods of melting gold, silver, and bronze
(casting or ingoting). As an ameteur astronomer I also know that gold
coatings are put on mirror type lenses to aid in the reflectivity of
IR light for purposes of gathering data in those wavelenghts.
(Aluminizing is used on mirrors for the visible-light wavelengths).
Coatings on optical lenses of all sorts are a frequent way of
passing,absorbing, or reflecting the desired wavelengths more
efficiently, many astronomical filters are made just to filter
particular bands of light and they depend heavily on specialized
coatings as well as color of the filter.

It stands to reason that if a filter begins life as a Shade #5
density and then has gold deposited on its 1st surface (the one
facing the light source) that its original filtering properties have
not been compromised but rather enhanced by the gold’s ability to
reflect IR wavelengths efficiently.

Just my 2 cents worth of agreement on the issue.
Paul Reilly
Colorado Srings, Colorado