PRESIDIUM Synthetic Ruby Identifier User Handbook Manual page 22

2.1 For testing on loose gemstones
Ensure your loose gemstone is wide enough to cover the Photo-
detector. It should be approximately 3mm in width. Your loose
gemstone should also not exceed 6mm in height to ensure that the
UV wavelength transmitted by the LED light source can be accurately
measured.
Place the loose gemstone over the Photo-detector (Fig 2.4).
Fig.2.4 Placing the loose gemstone on the Photo-detector
The flattest side of the stone should be placed face-down on the
Photo-detector.
Ensure that the Photo-detector is completely covered by the gemstone
so that the emitted wavelength is through the stone material.
Should the Photo-detector not be completely covered by the
gemstone, the emitted UV light will not be able to pass through the
stone, reaching the Photo-detector instead and will give an inaccurate
reading of the UV light transmittance ability of the stone material.
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