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Refraction liquids

What is the best liquid to buy to view cracks in rough gem stones so they can be faceted correctly?
Thank you in advance

I’m a beginner, but I will share the result of my mostly untested research regarding the specific stones I’m interested in cutting.

The liquids have different refractions just like the stones, thus, my list starts with the lowest refractions and the refracations go up as you continue reading.

The last two liquids on this list are expensive and dangerous. Initially I thought it would be convenient to use just one liquid to view all clear stones, but when I found out the cost of Gem Refractometer Liquid, it made more sense to me to use the cheaper liquids if possible, therefore, I have matched the liquids to the stone refractions in this list.

You save and reuse the liquid. On my first try, I found out that the residual dirt on my stone that wouldn’t come clean, will come off in the liquid, so I learned to cut the surface of the stone to remove residual dirt before using the liquid or else I’ll be reusing dirty liquid.

When I list multiple liquids, they are individual possibilities, not mixed together:

opal - water, olive oil, mineral oil, oil of cedar

moonstone, agate, calcedony, sunstone, rose quartz - clove oil, methyl salicylate

quartz, labradorite, beryl - cinnamon oil (if beryl, the cinnamon oil must be cassia)

topaz, apatite, andalusite, prehnite, tourmaline, kunzite, peridot, chrome diopside, tanzanite, idocrase, kyanite - methylene iodine

garnet, spinel, chrysoberyl - Gem Refractometer Liquid

1 Like

Hi Betty,
The key concept here is “close enough for jazz.” You are complicating things unduly…while if the RI of the immersion fluid and the gem are matched very closely, the gem’s surface will disappear entirely in the liquid and the inclusions will appear to float in the liquid, even if the gem’s RI differs somewhat from that of the liquid, the surface reflections will be much diminished and you will be able to see the inclusions with ease. This occurs as long as the RIs are somewhat close. The typical immersion fluid that is cheap and mostly non-toxic (and even used as a full strength treatment for scabies, I think) is benzyl benzoate, RI=1.56. Since quartz is 1.54-1.55 and corundum is 1.76 and garnets are about 1.74 to 1.81 and most other colored stones are somewhere in between those highs and lows, benzyl benzoate will do very nicely. You can buy it in bulk on ebay or from a chemical supplier. You could also use something like cinnamon oil or cassia oil, but these are skin irritants, so a little more troublesome (they are RI around 1.61). For all but the largest stones, about 4 ounces will be more than enough. When out in the field, even immersing in water or coating the stone with any available oil (RI~1.43) will help. Magnification is also a great help and I recommend getting a stereo zoom microscope and some indirect lighting (like LED penlights), which helps enormously, too. Maybe you got the idea for matching RIs from reading somewhere about SG liquids. If you were trying to measure SG by seeing whether the stone sank or floated in the liquid you would need a graded set of liquids of various SGs.

Beyond the RIs of the clove and cinnamon and other spice oils you do get into some pretty noxious products and I would not recommend using them for immersion, altho’ I did last year tip a whole bottle of RI liquid up and spill it all over my hand and I am still here…it was 1.79 liquid rather than the 1.81 stuff, which is yet again more toxic…and I don’t use the latter at all, since above 1.79 there are other ID strategies to use. Hope this helps…royjohn

@royjohn

If you do not use it for viewing, then what was your lapidary purpose for using a 1.79 liquid?

Maybe I wasn’t clear…I was talking about RI liquid, the liquid you use on your refractometer prism that I spilled on myself while measuring the RI of a stone. It wasn’t immersion fluid. -royjohn