I don't know SGC's methodology, but a microscope should work through shellac if the shellack is relatively clear. My microscope could saw a card's printing through a PSA holder. You have to be able to get the microscopic image in focus, and a thin film shouldn't prevent that. If somethings framed behind glass, then that can be too far away to get a proper focused look.
With old photos it can be a different situation, as you often have to look at the paper fibers to authenticate. Shellac could probably hide that view. I think shellac could cause legitimate authentication problems with an 1800s photograph. Though I can't recall ever having had a photo old or new that was shellacked, so I'm speculating. And, anyway, with a T206 you're examining the printing not the paper fibers.
Last edited by drc; 05-02-2013 at 01:28 AM.
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