testing colored gems: Do digital refractometers work?

[jeannius]

I recently got a big parcel of stone pulls from scrapped gold etc.. and some were obvious, but some I have had to do things like use chelsea filter, UV, loupe and refractometer. I have an older GIA refractometer but I cannot always get a read on it(could be the fluid, or the lens needs repolished-it has yellowed). I have recently seen that there are digital refractometers on the market for as low as about $150 and they don't need fluid/oil and give you an exact read out. Question is, how reliable/accurate are they? I remember they had a 'reflectometer' out a long time ago that was digital... but that disappeared from the market.

 

[arglthesheep]

not really we have one of it. The idea was to test stones > 1,81 RI as we are also dealing with many rarities. but the readings are not really reliable. Sometimes 3 Tests in the same position 3 different readings. Of good help in this lot screening is a rareearth magnet and UV. This will help to find most of the garnets and some other stones.
So now we have some RAMANs for difficult stones, which work pretty well and fast.

 

[Nosean]

The problem using a „digital refractometer“ you get only ONE reading. Yes, can be useful for gems with a RI over the limit like diamond, demantoid, zirkon, sphene ....

The classic analog refractometer gives you not only the RI, you get birefringence and whether the gem is amorph or cubic with one reading or uniaxial positiv or negative ( tetragonal, hexagonal or trigonal) or biaxial pos. or neg. ( orthorhombisch, monocline or tricline).

A stone with a RI of 1,762 - 1,770 ( after several reading you notices that the higher reading 1,770 is fix and the lower reading is variable) = uniaxial negativ with 0,008 birefringence so Corundum ( whether natural or synthetic or treated is another question).

The digital refractometer will give you only a reading between 1,762 and 1,770...