What is a Dichroscope and how do I use one?

What is a Dichroscope?
The first thing you need to know is...
Dichroism - The property of a mineral (in our case a gemstone) to show two different colors, or color shades through two different directions of the crystal.

Basically a Dichroscope is a tool that lets you view the different colors of a dichroic piece of rough (I know there are people that will ask... yes, trichroic stones like Andalusite will show all three, just two at a time while you rotate the rough, you will see three colors).

There are several different types of Dichroscopes, but the most common type is one made with Calcite (pictured above). Basically a Dichroscope, when you look through it will show you any dichroism that a gemstone/rough might have. It is used by most people for identifying whether a piece of rough is dichroic.

The reason knowing this information is handy is because it helps you identify rough. For example, a Garnet is not dichroic (color change Garnets can show an anomaly sometimes, but they are rare), Tourmaline is dichroic. So you can tell the difference between a piece of Garnet and Tourmaline by looking for the one that has dichroism.

Typically on a Garnet it will just look red in both windows, but Tourmaline will look red and purple (or pink, orange... what ever). See the pictures below, in the last frame you can see the two windows of Calcite inside the scope. Notice the color differences. One is hot pink the other is a darker purple/pink (it was tough to get a good picture, but you can see what I mean).

How I use one...
A Dichroscope is a very over looked tool, by faceters in general.

It is an ideal tool for getting a good idea of how the color(s) on a piece of rough are going to look in a finished gemstone. Dichroscopes are generally not expensive, and I think most faceters should have one in their tool collection (Gem Instruments). Most faceters have never used one, and if they have, they may not have thought of using it for getting an idea of color in a finished gemstone.

Have you ever had a piece of Tourmaline rough and you were not sure how it should be cut? A dark or different colored "c" axis?

What should you do with this type of rough? Well with a Dichroscope you can get a pretty good idea of what the color will be in the finished stone.

It will help you decide what is best, by letting you actually see the colors. Especially if you are an inexperienced cutter, and have not done it before. A Dichroscope is a very good learning tool.

In the picture above, notice that this piece of green Tourmaline actually has a blue/green axis, with an olive green on the other axis. This stone will cut to be a nice bright green stone when faceted (faceted with the blue/green axis up on the table, hopefully the rough will allow this. However it will be nice either way). In other words, if you mix the blue/green and the olive green, you will get a good idea of what the finished stone will look like. Keep in mind that there are some other factors to consider, like design shape and type. But in general this will give you a good idea of what the axis colors will mix like. Look at them and imagine what color they would combine to make.

If the colors through the Dichroscope were olive green and brown, then you could be pretty sure that the color of the finished stone would come out a muddy green. You would need to consider cutting a design that would minimize the poor color "c" axis, like cutting my "Smith Bar" which has very steep ends to help keep the "c" axis from mixing and darkening.

Do not forget that a Dichroscope will also help you orientate a piece of rough. By looking through the scope and turning a piece of rough you can judge where the color you want is strongest (identify the axis's). It is very helpful when orientating Sapphires, the light should be coming from over your shoulder in this case. When you see the best color up, this is the direction that you will generally want to show through the table of the finished stone.

By looking at a stone/rough through a Dichroscope you can;
1. Tell what the true colors are on each axis actually look like separately.
2. Orientate for axis and color.
3. Get a good idea of what the colors will look like when mixed in the cut stone.
4. Get a good quick identification of a piece of rough (I carry one at all the gem shows I attend). A piece of Garnet is a lot cheaper than a piece of Ruby, and it is not uncommon for them to be mixed. They are often found in the same areas and mines.

Here is a Quick list of Common Gem Stones (Dichroism);
Andalusite - Yes (trichroism)
Apatite - Yes, weak
Beryl - Yes, but usually weak
Chrysoberyl - Yes, but usually weak
Danburite - Yes, weak
Diopside - Yes, weak
Garnets - No (occasionally a color change Garnet will show an anomaly)
Iolite - Yes
Opal - No
Orthoclase - No
Peridot - Yes, but very weak
Quartz - No
Sapphire - Yes
Scapolite - Yes
Spinel - No (I have seen a couple that were color change and show an anomaly)
Sphene - Yes
Spodumene - Yes (Kunzite, Hiddenite...)
Tanzanite - Yes
Tourmaline - Yes
Topaz - Yes
Zircon - Yes

More articles about that will help you interpret the colors and how they will mix that you will see through the Dichroscope.

What are complimentary colors? What's a color wheel?

How do I cut a stone with different colors on different axis's?

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