Refractive Index List of Common Household Liquids

Gemologists may immerse gems in refraction fluids during examinations. This refractive index list of household liquids offers some common alternatives.

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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?
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

LiquidRefractive Index
alcohol, ethyl1.36
almond oil1.45-1.47
anise oil1.54-1.56
Canadian balsam1.53-1.55
cassia oil1.58-1.60
castor oil1.47-1.48
cedar wood oil1.51
cinnamon oil1.59-1.62
clove oil1.53
coconut oil1.43-1.46
cod liver oil1.46-1.48
corn oil1.47-1.48
cottonseed oil1.45-1.48
eucalyptus oil1.46-1.47
glycerol (glycerin oil)1.47
lemon oil1.47-1.48
linseed oil1.47-1.49
mineral oil1.47-1.48
neatsfoot oil1.47
olive oil1.44-1.47
palm oil1.44-1.46
peppermint oil1.46-1.47
rape seed oil1.47-1.48
safflower oil1.47-1.48
sandalwood oil1.50-1.51
sesame oil1.47
soybean oil1.47-1.48
tung oil1.49-1.52
wintergreen oil1.54

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


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.


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

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