I cannot find a reference (image) on this (exact) refractometer on the web. Obviously very old and far as I can tell will work great, all the parts and lighting/index wheel work like a fine tool you’d expect. I am not a patent search expert so the #178 patent pending means little to me. Some of the GIA literature points to them (Shipley I think) inventing some of these back in the 1930’s ish and beyond but this model is elusive, maybe the precursor to the more popular Duplex II. Anybody have more information on these units if they were widely manufactured/used?
Thanks!
Stuart
@StuartL55448 Where did you find this refractometer? It is very unique, and i have never seen one like it. Hopefully other members with be able to help answer your questions.
Goodwill, believe it or not. Very sturdy and it works fine. It says “Model 2” and #178 so presumably there are more out there, but I cannot find a reference, other than what I said originally. I emailed GIA but they didn’t get back to me so far.
Another Image of this antique GIA refractometer.
Stuart, what an amazing find! It’s incredible the things discovered at a goodwill or at a garage sale. 
Suggest you reach out to Jeff Wildman. His contact information is on the website. The company has done a lot of retrofits to refractometers (i.e. replacing the hemicylinder glass and calibrations) and may have seen one of these. It doesn’t hurt to ask.
How did you reach out to the GIA about this? I am surprised someone has not responded. Did you send an email to the GIA Museum: MuseumTours@gia.edu? One of the curators should respond.
I did a deep dive into the Patent Office archives and unfortunately, didn’t find a specific match. Not uncommon, when the product only has a “patent pending” placard. Sometimes the design is modified or contested before a patent is issued… and abandoned with new designs or litigation.
Still looking though, because that is a very unique piece of history you have! 
Cheers!
