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Question: Your article on gemstones and refraction liquids has a refractive index list for fluids frequently used in gemstone testing. But many of these are expensive and/or poisonous. Do you have a refractive index list of common household liquids that can be used for immersions? I’ve found information online for things like vegetable oils. Nevertheless, I’d really like to see a definitive, accurate list of “everyday fluids” that actual gemologists actually use. Also, do you have any preferences or tips for using these refraction liquids?
By International Gem Society 3 minute read
olive oil bottles

Looking for inexpensive refraction liquids for your gemological testing? You’ll find olive oil and other vegetable oils on our refractive index list of common household liquids. Photo by John Seb Barber. Licensed under CC By 2.0.

Refractive Index List of Common Household Liquids

Liquid Refractive Index
alcohol, ethyl 1.36
almond oil 1.45-1.47
anise oil 1.54-1.56
Canadian balsam 1.53-1.55
cassia oil 1.58-1.60
castor oil 1.47-1.48
cedar wood oil 1.51
cinnamon oil 1.59-1.62
clove oil 1.53
coconut oil 1.43-1.46
cod liver oil 1.46-1.48
corn oil 1.47-1.48
cottonseed oil 1.45-1.48
eucalyptus oil 1.46-1.47
glycerol (glycerin oil) 1.47
kerosene 1.45
lanolin 1.48
lemon oil 1.47-1.48
linseed oil 1.47-1.49
mineral oil 1.47-1.48
neatsfoot oil 1.47
olive oil 1.44-1.47
palm oil 1.44-1.46
peppermint oil 1.46-1.47
rape seed oil 1.47-1.48
safflower oil 1.47-1.48
sandalwood oil 1.50-1.51
sesame oil 1.47
soybean oil 1.47-1.48
tung oil 1.49-1.52
turpentine 1.47
water 1.33
wintergreen oil 1.54

Editor’s Note: This list was compiled from information provided by Donald Clark, CSM IMG, Dr. Gerald Wykoff, Dr. Clive Washington, Roy Kersey, and others.

Vegetable Oil Variations

Be aware that vegetable oils have variable properties. Even oils made from the same species of plant vary in chemical composition depending on things like plant varieties, where the plant grew, how much sun it got, etc. Nevertheless, most plant triglyceride oils (castor, corn, olive, soybean, for example) have fairly similar RIs. Tung oil is a little higher, but make sure it’s not adulterated. Clove oil is quite a bit higher.

Dr. Clive Washington

Refractol

Maybe it’s not quite a household liquid, but I use a product called Refractol. It’s clear, odorless, nontoxic, and has a listed RI of 1.567. If you buy it online, double check the listed RI. Some product has an RI of 1.52 to make it transparent to glass microscopic slides.

Keep in mind that oils do have variations in RI, and some household liquids, like turpentine, can be noxious.

Donald Clark, CSM IMG

(Editor’s note: Refractol may no longer be available).

Nail Polish Dryer

For looking into a stone under a microscope to find inclusions, I use a product called Sally Hansen Dry Kwik. It’s, of all things, nail polish dryer. In my opinion, it works better than Refractol.

Harold

Cinnamon Oil Pros and Cons

cinnamon oil - refractive index list

Photo by Cinnamon Vogue. Licensed under CC By-SA 2.0.

I myself use cinnamon oil. It has a pleasant, if strong, smell. Some warnings: it may eventually eat through the seal of its jar and might produce red welts on you if you get it on your face. (It did to me). Also, if you’re examining rough, some gem dealers may not like you giving them back scented stones. The dealers with whom I’ve done previous business have had no objections to my immersing their rough. Ask first.

Scentless Refractol may be better for some, but cinnamon oil is almost exactly the same RI as tourmaline and topaz. It would be quite good with spinel and corundum, too. Cinnamon oil does have a yellow color, so those who want absolutely clear fluid will have to look for something else.

Roy Kersey