Refractive Index Solution

A Refractive Index Solution can be used to examine the interior of a stone with more detail. If you place a piece of rough in a liquid that has a "refractive index" (R.I.) more like the R.I. of the rough, then the exterior walls will tend to disappear. It is mush easier to look into the stone for flaws or color zoning. One such material is called "REFRACTOL" and has an R.I. of 1.567. (Good news is that it has no odor!) Since quartz (citrine) has an R.I. of 1.54 it works pretty well.

To the left are 4 quartz rough pieces, and a bottle with REFRACTOL. REFRACTOL is an oily media, so it is a little messy to work with, but worth the effort.

Use a retractable stone holder or tweezers to hold the stone and immerse it in the liquid. See the next couple of pair of images with the stone backlighted only, then backlighted with the refractol. Notice how easy it is to see the "inside" with the use of this liquid media.

Notice that in the first two photos (same stone different angles) there is no real indication of strong color banding. After the stone is immersed in the refractol, the banding becomes quickly evident. To get the best color from this stone, the color bands should be placed parallel with the table. In this case the stone is free of internal flaws, but banding is present.

No Refractol
In Refractol

In the next pair of photos, the picture to the left is the rough and it has a fractured, uneven surface. It is hard to tell how much, if any of the damage is internal. When placed in the REFRACTOL (image below right), one fairly large internal fracture shows up. The good news, is that it is located near the back of the rough, not far from one of the surfaces, and hence it can be cut around without major loss. There is also some color zoning but it appears bidirectional and thus can safely be ignored. The stone needs to be oriented to cut out the fracture.

No Refractol
In Refractol

Safflower oil


Listed are a few of the more common oils and their refractive index. These can purchased at a drug or grocery store and can be used to aid in the proper alignment. Some smell good, others ...

Methyl Salicylate
(Oil of Wintergreen)


Clove oil


Color Zoning

Color zoning or banding is common in many minerals. Amethyst and citrine often have bands of color running though out the rough. See the first example of amethyst above in the refractol.

Sunstone often has color centers with the deepest red being located in a hazy cloud within the stone. Sometimes it has concentric circles of color with red in the center, green on the edges, and clear material around this.

Here is the best example of color zoning I could come up with. I took a piece of blue glass and glued it on a piece of clear glass. Maximum separation of color! and only about 20-25% has any color.

Now if this were tourmaline, then I might try to cut a bicolor gemstone with one color at each end. However, I am attempting to show how to place color to your advantage when we are not gong to cut a bicolored stone.

Ideally you want to place the color center low in the pavilion and have it cover as much of the stone as you can. By placing it low in the stone you gain one advantage, the color will be reflected throughout the stone. From the top you will see mostly the desired color and little else.

Unfortunately this is not a cure all for a stone with only a limited color center. The consequences of placing the color center near the bottom of the stone are illustrated in the series of pictures to the left.

As your eye move more in line with the girdle of the stone, the color fades, and it is obvious that the stone is not a solid color. By the time your eye is at the girdle level, the two parts of the stone become apparent.

The concept here is to put the color where it will do the most good, and put it where it is most likely to be seen after mounting in a piece of jewelry. (THE TOP!)

If this stone were placed in a bezel mount (like a class ring) then the blue color would show nicely from the top, and no one would be able to see the sides.

There is one other thing that can be learned from this placement. If you have a non desirable color center, or flaw in a stone, the last place you want to put it is near the bottom center of the stone. If you place it there it will be multiplied nicely around all the interior of the stone. Flaws should best be place near the girdle and as off center as possible.