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Best way to calibrate a refractometer

I just bought a new Fable refractometer. I tested it on synthetic corundum that I have and it looks like it’s off about .04.

What is the best way to calibrate it?

Do they calibrate it? the one I have I don’t remember it’s brand name… but never needed to calibrate. Is it a digital one… Can you share a picture please.

The refractometer doesn’t need to be calibrated. That is done at the factory. I was hoping to know if there was a gemstone that has such a pronounced reading that I would know if my refractometer is correct or if it is off a little…

Thank you. I have synthetic spinels and synthetic corundum in my collection. Thanks for the tip.

I will have to do some checking, as I always thought that quartz was the most invariant gem…try that, also. You should be closer than 0.04…this is why I always tell folks that the Chinese refractometer is OK, just get a return privilege and check it on some quartz as soon as you get it. You also need a yellow filter or single wavelength light source to be sure you have an exact reading. Your idea of where 589 nm is may be off, but it shouldn’t be off by 0.04. If using white light, you are reading at the yellow, right? -royjohn

My refractometer comes with its own internal light source. I checked it against some synthetic corundum and spinel and it gave an RI reading for both those stones, so I imagine that the refractometer is working properly.

The light source of the refractometer can run on AA batteries as well as being plugged into the wall so it is very convenient. It also has a scale that goes to two (2) decimal places.

Yes, OK, so it has a light source, but is the light source white light or monochromatic yellow light. If you have a monochromatic light source or a yellow filter, you see only a shadow edge (or two shadow edges for a birefringent gem), whereas if you are reading with white light, you see a small rainbow and have to read the yellow portion to get an exact reading. So which is it? -royjohn

It’s a yellow light, so all I get to see is the shadow edge.

OK, so you should have a scale divided into tenths…1.40, 1.41, 1.42, etc., so you should be able to read to about 0.002 or 0.0025. Quartz is birefringent and should read 1.544 and 1.553. So if you try a few samples of clear quartz, amethyst and/or citrine and don’t get that value, your instrument is off by whatever you are reading as the error for quartz. You can still use the instrument, but you’ll have to correct your readings by whatever error you read. -royjohn

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Thank you very much for the tip… Now I just have to find a nice piece of quartz or citrine to use.

A sodium light source provides the “standard” wavelength of yellow light yielding sharp Refractometer readings. Scientifically measured Refractive Indexes for minerals and gems are usually derived from this standard wavelength, or from other referenced standard wavelengths. If it was worth the investment of a Refractometer, and accuracy of the readings are the goal, purchase a sodium vapor lamp intended for this purpose. A yellow filter is somewhat useful, but not as accurate. Most ‘casual’ users of Refractometers lack the knowledge how a Refractometers works and the understanding of Optical Crystallography to begin to use one to its potential. I built a Refractometer years ago as a high school Science Fair project which does not require Refractive Index Oil! Can you figure out how it worked? Hint: I made the heart of the Refractometer with a Lee Faceting machine. The Lynchburg Gem and Minerals Society recently posted an introduction to crystallography on YouTube titled “Crystallography by Dave Woolley” which is the background preparation for a lecture I hope to make at the United States Faceters Guild’s, “Franklin Faceters Frolic” in Franklin, North Carolina at the end of July. Look for the lecture to be posted in the USFG’s newsletter in the near future, titled “Useful Crystallography”. The YouTube video and follow up article are to assist with increase successes in faceting, and with the background understand of Optical Crystallography for the use of a Refractometer.

Thank you CitroenDave!

I’m actually fascinated by crystallography… I just haven’t had the time or patience to read more about it… When I first got interested in gemology I was working in Tanzania in telecom and all I was doing back then was studying more telecom engineering, photography and whatever time I had left was for gemology. I was lucky that my boss’s passion for gemology let him teach me a thing or two, introduced me to various gem brokers in the country where I purchased various rubies, sapphires and tanzanite with his assistance.

My personal refractometer already has a built in sodium lamp. It doesn’t have any area where you can attach a flashlight or other light source. It also has a second light I can turn on if the standard light is insufficient.

It’s a very decent refractometer.

In all honesty I have no idea how you would go about building a refractometer let alone one that doesn’t require any oil to use. I would definitely like to learn more about that.

If you have any links i would be grateful to learn more about this.

I’m here to learn since I know so little. A little knowledge is a dangerous thing.

With what little knowledge I have i have used to build a small business when I lost my job running a company (it went bankrupt with all the lockdowns)… So now I am using all my connections and knowledge for this endeavor.

I just purchased a smoky quartz to check on my refractometer.

I’ve been using synthetic corundum and spinel to see if my refractometer olives accurate readings and it appears that it does.

At this point I need to pick an online gemology program to fill in the many holes in my knowledge and to be able to ask experts questions that come up.

The online course here is the most affordable, but I’m not sure if you actually get to ask questions to an actual genologist as part of the course.

It looks like you can with GIA and the GEM A online courses, so I have a lot more research to do.

Thanks for the info.


Good morning! It is very satisfying to know some of my ideas are useful. I am a retired geologist, lifelong rock hound, and casual faceter. (Also a Citroen automobile fanatic.) I am in the process of fixing my house to sell, and moving to Central Florida.

The GIA had a good start with good intentions. John Sinkankas, a founder of GIA, was a mentor; we both were members of the Washington Gem Lapidary and Mineral Society many years ago. GIA’s courses are probably good but as others companies, their leadership got led astray with greed. Have you followed the Jewelry Television-Sunstone case? Look it up. If you are going into this business you need to be aware of the problem. Robert James, ISG, is the only current source that I trust to keep industry on track.

Gemology can be learned with a couple of books, much less expensive than paying for courses.

The Refractometer can be tricky in application. A casual use can help with gem identification. But ‘causal use’ always needs to be augmented with other gem identification techniques. For unmounted stones, Specific Gravity, Magnetic Susceptibility, are easy to use, powerful techniques. I published a S.G. short-cut in the Australian Faceters Guild newsletter which I might be able to find, if you like.

Successful Refractive Index determination requires a full knowledge of the crystal systems, what I am working on now in my writing, and all the subtle techniques that can be applied with a Refractometer. For most people a Refractometer requires complete knowledge of the crystal systems, a good understanding of Optic Science, of the Refractometer techniques and lots of practice. A good analogy is the Petrographic Microscope. While the P.M. performs several well know mineral identification tests, there are nearly 200 types of tests it can perform. The Refractometer is much simpler than a Petrographic Microscope but its tests are based on the same Optic Science.

The British Gemology Institute, a government sponsored agency, posted a GPS equivalent of a road map for Refractive Index use. In short order, it gave all the twist and turns of steps for thorough testing with out much of the underlying science behind those steps. EASY TO USE.

The simple crystal system gems use simple Refractometer steps; ‘casual use’ people are OK . The Biaxial gems can get complicated and that is where most people give up.

I have packed my British document and it will be months before I can unpack it. I printed it on a poster board. I was disappointed (back when I copied it off the internet) that the British Gemology Institute took the document down. I would suggest asking if anyone has a copy of that file in their computer that they might share. It was the only completer “owners manual” I ever found for use, with out requiring intensive studies of expensive courses. This is after I wrote my own 12 page instruction sheet as I figured things out. I currently am not proficient in the use of a Refractometer as I let down on the recommended practice.

Good luck with your new business! If you are interested in faceting, Google “Scratches from the Master Lap”. “The Beale/Woolley Depth of Cut Indicator” changed history. And Join the United States, Australian, or British Faceters Guild. Attached is some background information in faceting.

Best regards,

For my Science Fair Refractometer, I cut cylinders of unknown transparent minerals with the Lee Faceting head. Cut in half, lengthwise, each half cylinder was mounted like the high refractive index glass or synthetic half cylinder in a conventional Refractometer. With a two mounted razor blades to make a slit light source and a movable observation arm with a protractor beneath plus appropriate lenses, I was able to make at least one strong reading. This was well before I had any understanding of optical crystallography science. Primitive, but had some successes. All, email me for copies of other documents related to faceting.


Thanks for the info. I myself love Fiats. I like the old 70s Fiats especially the Fiat Spider 2000. I had one of those and they were great fun to restore then drive… Only drawback was the lack of air-conditioning in my 1977 Fiat spider.

I’d greatly appreciate some suggestions for books on gemology. I’ve been reading about Professor Hanneman. He was a professor of chemistry and self taught genologist… I bought one of his books and his specific gravity scale and his filter sets based on spectroscopy… They were inexpensive and looked interesting. They’re currently languishing in Philippine customs.

One of the reasons I’m thinking of getting formal Gemological training is so that I can eventually establish my own Laboratory here. We do t actually have a Gemological Laboratory in the country. I have to go to Thailand to get anything certified and I’m not alone, so becoming a GIA or Gem-A certified genologist would probably be quite lucrative.

I’d really like to get a copy of the paper on how to utilize a refractometer.

I’m also looking into spectrometers because they can supposedly differentiate between natural a d synthetic gemstones rather quickly.

Again, it’s one of professor Hanneman’s books. I’ve tracked down a copy and am waiting for it to get shipped here then get stuck in customs.

I’m a self taught telecom expert (wormed as an Ericsson senior manager in Africa for many years), self taught photographer also.

If you really think about it, most of any degree you get from a university is from you teaching yourself and I have a few letters behind my name so I know I can teach myself as I have taught at university before as well.

I have a rather small collection of gemstones I’ve bought over the years as has my wife and we’ve inherited a few stones. All in all j would guess we have about 60 to 100 gemstones that I am cataloguing.

I’m also using them as a way if learning about gemology. I’ve bought a complete set of synthetic corundum and spinel for use as comparison as well.

I’m probably going to buy some synthetic emerald as well so I can have a more complete library of synthetic gems to look through.

I’m also still learning how to use a microscope. First one I’ve used since I was at university, except this new one has a 36 megapixel camera but in. It’s just hard to use since the idiot sales people forgot to include a 50 cent piece that renders my gemholder useless, so I have to handhold any and all my specimens right now.

Why haven’t they, as in scientists, redesigned the refractometer so that it doesn’t have to use the toxic oil? Or get higher readings? I would have thought that 100 years would be sufficient time to make improvements in this device.

I’ve read mixed reviews about digital refractometers and Dr. Hanneman’s device… I forget what it’s called.

I would appreciate any and all links to books, papers, articles, cheat sheets etc as short cuts to learning gemology and more importantly sorting synthetics from natural stones.

Best regards,



BGI’s easy-to-use chart for the Refractometer remains packed for my move to Florida. I have no idea when it will be unpacked, or which box it is in. Best idea is to post a request to see if anyone else downloaded it several years ago. Does anyone have a copy?

My two kids faceted their first standard round brilliants at age 4. In spite of the hype of a 20 year apprentice, it can’t be very difficult . . . no offence to 4 year old’s. I built a faceting machine in 15 minutes! Given that I had an electric driven flat lap machine. My rock club members cut their first facets with that machine.

I would not recommend my 12 pager on Refractometer use. it was too darn technical for me, now buried in an obscure folder somewhere in my old, packed computer.

Citroen DS placed third in the Car of the Century competition after the Model T and the Austin Mini Cooper. Just goes to show ignorance. The 1955-75 DS Citroen was designed in large part under German occupation during WW II. The Michelin family protected the several engineers at their county farm where the were free to pursue any idea. The Michelin family of tire fame and Citroen knew cars were going to be needed after the war, they made good use of time… Citroen was very secretive of the men and their ideas. I think I am the first to publish in English a list of the 180 features, many that I discovered while working on my 14 used cars. Only i/3 third of their prototyped ideas were used! Other inventions found their way into subsequent Citroen models through the years… Attached is a partial history. Also check out Citron Car Club of Canada’s newsletter, Citroenvie, Spring 2010 and later issues where I list the 180 features. 56 of which changed industries. The DS was considered the most important Product of the Century for its many contributions to industries. An unedited version is attached. The DS Citroen was given the “Product of the Century” award in recognition of the engineering inventions that changed many industries.

Ops, No attachments allowed.

Email me with request on either topic: Faceting and Citroens. Tell me a little about your interests.

Best regards,


I found it!

I have located my copy of a simple user’s guide for the Refractometer that years ago was posted at either The British Gemological Institute or The Gemological Association of Great Britain; I do not remember which. There is no author listed. I remember, that it was taken down from the site shortly after I captured it.

I am preparing a two unit presentation to get faceters and gem enthusiast up to speed. The first is a U Tube video titled “Crystallography by Dave Woolley” that can also be found at the Lynchburg Gem and Mineral Society’s home site, under videos. It provides the visualizations necessary for the second presentation.

The second presentation will include a hands on version of the first and be titled “Useful Crystallography and Refractometry” to be given at the USFG Franklin Faceters Frolic, Saturday July 31 at 1 pm. Franklin, North Carolina, My text will get you up to speed for the Refractometer user’s guide. If I can not make it in person, I plan on making them available as hand outs. I expect that it will also be posted in the United States Faceters Guild, newsletter. I will try to include the Refractometer users guide in the newsletter if it meets copyright guidelines.

Hang on while I complete the second unit and get things sorted out.