Abstract Gems & Gemology, Spring 2013, Vol. 49, No. 1

The “Glet Filling”: The Filling of the Cracks in Precious Stones Under Scrutiny

This short article discusses several important aspects of fracture filling in colored stones and diamonds: the difference in market value between included and filled stones, especially in high-quality goods; the impact of nondisclosure within the supply chain; different methods of filling and their limitations; and methods of detection.

Several similar methods of filling diamond cracks (“glets”) have been developed under such names as Yehuda and Koss (Israel) and Diascence, Genesis Enhanced, and Goldman Oved (New York). One of the filling methods discussed in more detail, the Koss system created more than ten years ago, limits the rainbow or “flash” effect, the yellow-orange color flashing into electric blue under darkfield microscopy) characteristic of many other filling methods.

Regardless of the method, the visual improvement achieved from filling cracks with oils or the modern vitreous, high-RI materials is temporary: After a few months or a few years, the tears and cracks become visible. Fillers degrade with time and by environmental conditions. Some dry out to reveal noticeable residue; others deteriorate with exposures to ultrasound, ultraviolet, heat, acids, and chemical cleaners.

Several methods of detecting fillers are briefly mentioned. Gemologists commonly use magnification to observe bubbles, filler textures, the flash effect, and filler deterioration. Advanced methods such as scanning electron microscopy, X-ray fluorescence analysis, and Raman spectroscopy easily reveal the presence of filled glets.

Abstracted by Edward R. Blomgren