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Here's something you may not know. A modern welding mask is more than a helmet with a tinted window in front. Nowadays the window has a polarized coating applied to it, which turns opaque when electricity is applied. A broad sensor plate above the window detects the intense light of a welding torch, and triggers an electric current, blocking the light and protecting the mechanic's eyesight. Pictured here is the circuitry inside the mask that makes it all work. Unfortunately, this particular mask doesn't work. Instead of rushing out to buy a new one for $200, Andy has elected to repair it.