• The Poor Man's Polariscope

    8 April 2016

    Poor Man's Polariscope

    From this week's ISG Journey Thru Gemology

    Based on a multi-million dollar advertising campaign by the 800 pound gorilla in this industry, there is a misconception that doing professional level gemology requires you to spend tens of thousands of dollars on education, and almost that much on gemological equipment. I hate to break it to those of you who, just like I did, spend that money with the 800 pound gorilla because in the end, this gemology thing is not some magical, mystical knowledge. As my good friend Dr. Bill Hanneman has been trying to tell us for decades, this gemology thing can be done with very basic tools if we just slow down and learn what we are doing. So today, I wanted to share with you what I believe is some pretty amazing gemology, done with a poor man's polariscope.

    Before we start a couple of notices: there are quite a few GIF files in this edition, so if anyone is prone to motion sickness you might want to take your pharmaceuticals before reading this. Also, before we look at our poor man's polariscope we should review exactly how the polariscope works. For that we, of course, turn to our poor man's graphics done on our 17 year old iMac Blueberry.


    Depicted in this graphic at left, ambient light is made up of light waves traveling in all directions, a total mish-mash of light surrounding us daily. Even a light bulb of a polariscope gives off light that looks....well sort of....like the depiction at left.

    To make a polariscope work we first need a polarizing filter. This is a filter that allows light traveling in only one wave direction to pass through the filter.


    As demonstrated with the graphic at left, when a polarizing filter is in place the light allowed to pass through is restricted to a single plane of travel direction, known as "plane polarized light".



    If you add a second polarizing filter you can quite literally turn the light on and off, meaning you can block all light or just the plane polarized light from passing.

    When the filters are aligned in the same direction of polarization, the light is allows to pass through.


    When one filter is turned at a 90 degree angle to the other, the second filter changes the direction of allowable light wave and the result is that the light wave is blocked.

    This is what happens when you turn the polarizing filters of your polariscope from light to dark. Aligned and not aligned.

    When you put the polarizing filters in the dark position (as seen above) and then place a double refractive gemstone in between and turn the stone, the stone will turn from dark to light.

    This is confirmation of a double refractive stone (we won't go to the ADR thing in this newsletter).

    But why does a double refractive (DR) gemstone turn from dark to light in darkened polarizing filters?

    The answer can be seen at left. The gemstone's DR nature essentially serves as a third polarizing filter that changes the path of light between our two polarizing filters, causing the light to change direction and be transmitted.

    When the gemstone is aligned with the second filter, it is dark since it is polarizing the light in the same direction as the filter.

    But when the gemstone is turned different than either of the two filters, it alters the light path to a degree that the light travels on through the filter.

    Now, the question is: Do you need an expensive polariscope to get this reaction, or can you do the same thing with say....a pair of cheap sunglasses with polarizing lenses. Let's test this out using a pair of cheap sunglasses from the local 7-11 and a polarizing filter from our ISG Refractometer.

    Sure enough, when I take both of these out into the sunlight and hold the polarizing filter to one lens of our sunglasses, the light becomes "plane polarized" going from dark to light as the filter is turned. The turning of the filter causes the light to be blocked when the polarizing filter and polarizing lens are crossed at 90 degree angles.


    I went to our Destructive Gemological Tools Cabinet and pulled out our trusty carbon-steel bladed hacksaw, and prepared the sunglasses for further study and photography.



    Here is the set-up with my Meiji Techno Microscope base. By removing the microscope head and carefully placing the polarizing sunglass filters in just the right and perfect position, using Scotch™ tape, I was able to create my own Poor Man's Polariscope and testing was ready to begin.


    At left you can see that my poor man's polariscope works pretty darned good in the camera, but what happens when I put a gemstone in between the lenses?



    No question about it, our poor man's polariscope gives us a clear and diagnostic double refractive reaction from this hydrothermal created citrine I borrowed from the ISG Created and Treated Gemstones course materials.


    OK, that works, but what about using a conoscope and finding the optic interference figures? That will be the real test of our poor man's polariscope.

    I think you will be impressed with the results below.




    I have to be honest with you, the bull's-eye interference figure of this citrine is pretty far-out, in my opinion. Considering that we are quite literally looking through nothing more than the polarizing lenses of a pair of cheap sunglasses, if you compare this bull's-eye interference figure with any image in any gemology textbook in the world, this is pretty darned impressive.



    Even more impressive is this uniaxial "cross-hair" figure in a created ruby that did not even need a conoscope to view through our sunglasses. (thank you N8 for finding this one)

    The toughest interference figure to photograph, even with very expensive equipment, is the biaxial. However, using a danburite crystal and our poor man's polariscope, I believe you will find the images below to once again be pretty much on par with any of the textbook images out there.

    Thank you, Dr. Hanneman!

    If there is anyone in this industry that deserves recognition and some kind of major award, it is Dr. William Hanneman. For years Dr. Hanneman extolled the virtues of knowledge and practical applications, and shunning the need for high cost equipment and overly-expensive educational courses. It took me a long time to finally come around since, after all, I am a product of that 800 pound gorilla like so many others in this industry. But with the teaching of folks like Dr. Hanneman, Alan Hodgkinson, Ian Mercer and a myriad of others out there now, it has become clear that this gemology thing...it's not rocket science. It's not some magical, mystical knowledge that one can only get from one source and for high dollar cost.

    This gemology thing is about knowledge, practical applications of optical concepts, and once in a while just finding ways to do some poor man's testing.

    Perhaps it was best summed up by Ian Mercer, former Education Director of the Gem-A when I had the honor to work with him years ago. Ian summed up the goal of his teaching of gemology, and I will never forget this:

    "I want to be able to drop you into a field in the outback of Africa, with no other tools than what you can carry in your shirt pocket, and you be able to do gemology." (Ian Mercer, AGTA GemFair Tucson 2003)

    That, my friends, is not "poor man's gemology". That is professional gemology taken to the highest apex.

    Robert James FGA, GG
    President, International School of Gemology