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RI liquids to separate natural from synthetic

Can you use different oils like cinnamon oil, cedar oil, etc to see the growth patterns or striations of gemstones like corundum to separate natural from synthetic stones?

I know you can immerse corundum in cinnamon oil to see whether they have had Berrylium or titanium heat treatments… and to isolate specific inclusions. Can you also use it to see the striations or growth patterns within the gemstone?

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I wouldn’t trust common oils to determine genuine from synthetic stones. For heat treatment, its best to use a microscope. The oils will help striations and fractures to stand out, but I would ask a Gem(m)ologist to know for sure. Synthetic rubies and sapphires are well made, so common 'old wives tales, won’t cut it. Its one thing just to have an idea for yourself, but if you sell to others, you must be sure, or at least let them know you have no idea and you sell at a synthetic price.,

The IGS entry here on flame fusion synthetics recommends either a polariscope or immersion in a high RI liquid to aid in seeing the curved striae. Liddicoat reportedly suggested either methylene tri-iodide (RI=1.8) or bromoform (RI=1.59). MTI is very toxic, so I wouldn’t use that. The oils you mention (cinnamon, cedar) would be about RI=1.63, so they would be a good substitute for the other two mentioned…I think both of those are toxic. You could also use benzyl benzoate, which is actually used as a topical medication for scabies (RI=1.57). The cinnamon and cedar oils might be a skin irritant, but not really dangerous. I’d have to mention that some authorities mention the curved striae, but neither immersion nor the polariscope, so the striae are not that difficult to see with enough magnification. You do have to move the stone around, as striae which look straight from one direction may actually be curved if seen from another direction. If I remember right, about 30X is recommended, but check your references to be certain. This is another instance of a good microscope with darkfield illumination as well as direct light being worth its weight in gold (or gems…haha) for the gemologist. A lot of synthetics and other species have to be distinguished by their inclusions. HTH, royjohn


I mis-spoke in my last post…it is diiodomethane, not triiodo that Liddicoat recommends. -royjohn

@royjohn thanks. I remember reading about using RI liquids on this website and another one or book. I think it must have been one of his or mentioned by someone else.

I do have a very good microscope that I use, but I’ve always found it difficult to get to see the straie. I’ve found it much easier to see the straie under the polariscope when submerged in high RI liquids.

Cinnamon oil and cedarwood oil are both skin irritants but are not toxic compared to diiodomethane. They are also far easier to obtain here in the Philippines. I haven’t been able to find a vendor here for diiodomethane.

The best liquid to use I think is cedarwood oil since it has barely any coloring. I’m using perfume-grade cedar wood oil. Cinnamon oil has a very yellow color and a very strong odor that permeates the air when I use it, and it has a tendency of staining everything if not cleaned up immediately.

I’ve used the high RI immersion technique on both the polariscope and microscope, but I find it more difficult to do on the microscope since I use beakers to hold the RI liquid. I will need to purchase Pietri dishes for the submersion of the gemstones.

It also does a great job of revealing all the inclusions. I’ll upload some photos from my microscope when i get around to take some photos of the various gemstones. I’ll probably start by taking photos from my library of synthetics and then compare them with the natural stones. I’m not sure if anyone here will be interested in seeing the results.

this article about using UV light in analysis of corundum is interesting

I’ve also found that many synthetics coming from china are now heat treated as well to improve the colors and mask the synthetic origin of the stones.

Hello Daniel,
You are certainly working at this gemology stuff! The benzyl benzoate, while slightly lower in RI, is a lot less problematical than the spice oils and probably about the same price or cheaper…but if cedarwood is what you can most conveniently get, it will work. I have some cassia oil around here somewhere that I used until I got some benzyl benzoate. Benzyl benzoate is easily found on ebay, but IDK how easy it is to get shipped to the Phillipines.

Finding the curved striae is important, so use whatever method you are sure of. Of course another clue on flame fusion synthetics is their “too good to be true” color. I have never seen any that had much of a color modifier like most natural stones. That does not mean that you couldn’t find a natural stone with that incredible saturated color, just that it is unlikely.

You are certainly right that the immersion fluids help with inclusion detection. If you are a gemology student and have not used immersion fluids and your microscope, you are in for a treat. It is just magic! -royjohn

Benzyl benzoate is not available here right now… at least not easily. I’m sure all these chemicals can be found but I don’t know where to source them. So it leaves me with the spice oils. The cedarwood oil is excellent since what I have been able to procure is nearly colorless.

I think working hard is overrated especially when there is a way to reduce the amount of time it takes to find the striae. The oil immersion works so well that you can see it with a loupe or just using your smartphone camera at 4-10x magnification. I will be using my microscope otherwise I would have wasted a thousand dollars on a microscope with darkfield illuminations etc…

I am a student in everything. Currently studying gemology and waiting for the Gem-A online classes to start. I’m sure a self-taught gemologist would be ok, but I need the assurance of a professional letting me know that what I’m doing is correct and that my analysis is correct since I don’t want to be legally and financially liable. We have a small jewelry business and I need to make sure that the gemstones we are purchasing for our customers are what we say they are. We sell both natural and synthetic gemstones in our bespoke jewelry. It all depends on what our customers want.

I, therefore, need to ensure that my suppliers are indeed providing me with natural and not synthetic gemstones when I purchase natural ones. I’ve already discovered that most peridot being sold in the country is glass. We only have two gemological laboratories in the country and they are both currently closed due to Covid. There is therefore a rampant abuse by some suppliers selling whatever they want to distributors. I think I am one of the few people in the country with a specific gravity balance.

Anyway, I know that my stones are natural or synthetic and I feel comfortable telling my customers what they are buying is what it is.

I’ve been using my microscope to find the striae and it takes me forever. I’m sure the oil immersion will greatly reduce the time it takes me to find the striae. I’m not sure if anyone is interested in what the results are, but I will start photographing the gemstones and the inclusions, etc. I just need to figure out a way to position the stones in the oil to see the different angles. I’m thinking of using hot glue to make little transparent stands for the gems to sit in while immersed in the oil. Any advice on how to position the gemstones in the oil?

Hi Daniel,

Yes, of course you need a credential in the jewelry business and the Gem-A course is a good one. You will have fun with it. Looking at suppliers of benzyl benzoate on Ebay, I do not see that they prohibit shipping to the Phillipines, but I am sure that your cedarwood oil will work fine.

Positioning in an immersion cell can be problematical. If you had a square one, you might more easily prop a stone up against the sides. Here it is easy to source glass marbles and such and that might help provide a rough surface where you could wedge your stone into the right alignment. Manipulating with gem tweezers is possible, but not fun. You might find it possible to rig up a wire stand in the immersion cell that would help. The hot glue may also work. Or a plexiglass (acrylic) stand with various sized holes in it. It is easy to drill and glue together.

As you get further along in this, you may find that seeing natural inclusions eliminates the need to find straie in some cases, as will seeing bubbles that indicate synthetic. But the straie are confirmatory. Perhaps you already know all this. Not that many completely flawless natural stones, which of course raises suspicion of synthetic when the stone is clear of them.

If you are looking to just separate peridot from glass, it is easy just by looking at the “rainbows” in the stone. Peridot, because of its high birefringence, will always show pairs of rainbows next to each other, while glass, being singly refractive, will only show single rainbows. This and other details of “visual gemology” are covered in Hanneman’s book, Affordable Gemology. IDK if any of the gemology courses teach visual gemology.

You will be very proud when you can attach FGA to your name. It is a great credential. Best of luck!


Hi @royjohn,

The problem with importing benzyl benzoate has more to do with customs and logistics companies (such as FedEx etc). I was told I need a special permit to import it since it is quite toxic.

I’m using a chemistry beaker as my immersion cell as it allows light through it. I’m also using a bit of hot glue that I have made in a few different shapes to prop the stones up against so that I can have a better angle to look at it with my microscope.

I’m going to try to make a little wire cage of the gemstone out of some copper wire I have since a problem I have found is that I end up with bubbles under the stones that sometimes look like they are inside the stone through the microscope… so the wire stand may eliminate these bubbles.

I like Hanneman’s book and I keep referring to it for many of the visual cues.

For peridot identification, I’ve used the RI, Spectroscope, SG, and magnetism to verify that it is peridot. I’ve bought peridot from various suppliers and have found that 4/5 have been glass. Since there are no gemological labs in the country, some of the suppliers agreed to refund me. Others have not (these I will no longer be purchasing from). The ones I have had to keep have gone into my gemstone library.

Thanks for the heads-up about the rainbows. How do I see the rainbow? Using direct light with a loupe?

Thanks for the information and advice.


Hi Daniel,

You seem to have your gem ID methods in hand. Benzyl benzoate is not very toxic…in fact, it is

used as a topical medicine for scabies. That, of course, does not help when authorities are telling

you otherwise. It is readily available on ebay, and I think when I looked I did not see that they

listed the Philippines as a country that they do not ship to, so you should check there.

Looking into a faceted gemstone, you will see rainbows caused by refraction from the various

light sources about. The best way to view them would be with a single light source, say from a

small LED torch with a cap with a slit in it placed over the light. Usually I just look at whatever

rainbows I see from whatever light source there is. This shows me whether the rainbows are paired

(birefringence) or not. Sometimes they overlap, as in the case of quartz (small birefringence) and

topaz. You learn the patterns of the various gems after a while. A single light source would be

required to see the size of the circle of rainbows to estimate RI as Hannemann details.