Spectroscope Instructions

While based on sophisticated science, the spectroscope itself is a simple device. There are only a couple of adjustments; one for focusing and one for adjusting the amount of light entering the end. If you have the advanced model, there is also a separate focus for the calibrated scale and an adjustment for the scale’s position.


To Start


When your spectroscope arrives, point it towards a window or bright light. You should see a rectangular shaped rainbow spectrum, like the picture above. If not, make sure you are looking through the right end.

If you have an IGS Advanced spectroscope, you should also see a calibrated scale. If it is not immediately visible, try moving your head slightly to either side. Find the scale adjustment and turn it. You will see the scale move from side to side as you turn the adjustment.

Step Two

Next, place your spectroscope it its stand along with a gem of know identity. A natural or synthetic ruby is excellent for this purpose. Set it up for observing transmitted light. (For details of spectroscopic techniques, go to “The Spectroscope” in our Reference Library.)

Adjust the Light Opening

The next step is to adjust the amount of light entering the spectroscope. Slowly turn the adjustable slit back and forth to each extreme. Watch the spectrum as you do this. As you adjust the light opening, the absorption lines will come into view and then fade out. You want to adjust the light so the absorption lines have maximum visibility.

If you do not find the absorption lines, make sure the light is passing through the gem and into the end of your spectroscope. Turn off all the other room lights so they are not affecting your reading. Make sure you are using a gem with a distinct absorption pattern. (Ruby is excellent for this.) If you are still having trouble finding the absorption pattern, you are not looking straight down the tube. Set the light opening to the middle position and move your head slightly from side to side.


Once you have the absorption lines highlighted, you need to focus the spectroscope. Do this by sliding the tube in and out. You will notice that the lines do not come clear all at once. When one end of the spectrum is in focus, the other end will be slightly fuzzy. It sometimes takes more than one focusing to see all the significant lines.

Adjust Scale


If you have an IGS Advanced Prism Spectroscope, now is the time to use the scale. Slide the focus tube in and out until the scale is clear and easy to read.

Ruby displays strong double lines at 692.8, 694.2, 475, and 476.5 nm. Choose a strong line, such as 475. With the adjustment screw, move the scale so it lines up with the absorption line you are viewing. You now have your scale properly adjusted. It may need subtle adjustments with other stones, but very little. That is, unless you move it between stones.

More Reading

This is the basic procedure for setting up your spectroscope. For more details on spectroscope testing, see our article “The Spectroscope” in our Reference Library.



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