What is GemPen?

GemPen is a portable, battery powered, screening device for diamonds specially designed for the working gemmologist. The technology utilizes specialized UV filtering providing users with the means to efficiently and swiftly indicate whether a diamond is natural, synthetic (man-made) or treated (improved).

How does it work?

After GemPen is turned on and directed towards a diamond a fluorescing effect may occur. By analyzing this effect, certain conclusions can be deducted. GemPen gives instant indicative results.


GemPen utilizes unique combinations of UV-wave lengths and filtering provoking variable fluorescence in diamonds. With this so called USOF (Ultra Spectrum Optical Filtering) technology, GemPen showcases unique fluorescing effects, providing results on treatments and synthetics normally not visible with other UV-light products. The combination of calibrated lighting and filtering distinguishes GemPen from other UV-light devices – with consistent results and broader use cases.


GemPen comes with four different filters used on differing occasions based on gemstone and manipulation type. For optimal results, all four filters should be used, in particular to indicate treatments.

Interpreting results

First of all it is recommended to initially type test the gemstone(s) to ascertain the actual type of stone before testing with GemPen. To help users interpret the photoluminescence effects (fluorescence and phosphorescence) correctly, GemPen comes complete with a Diamond Map and a Test Tree for reference.

Interpretation Basics

Approx. 35% of all natural diamond show some degree of fluorescence from inert to strong.

If a natural diamond show fluorescence in Filter 1 it`s normally stronger with Filter 4, while a synthetic diamond show stronger fluorescence with Filter 1 and inert to weak with Filter 4.

  • Diamonds that only fluoresce in blue-bluish white (with Filter 1 & 4) can be identified as natural diamonds
  • Diamonds that fluoresce in other colours can be identified as synthetics
  • Diamonds that fluoresce in other colours and in some cases also show some phosphorescence can be identified as synthetics
  • Diamonds that shows a moderate to strong yellowish green fluorescence and a strong phosphorescence can be identified as synthetics (typically HPHT)
  • Diamonds that show a purplish blue fluorescence indicates HPHT treated natural diamond
  • Diamonds that both fluoresce and phosphoresce in strong blue can be identified as synthetic