Fissure filling in spinel
By Dr. Michael S. Krzemnicki, first published in Facette 30 (March 2026)
The practice of filling fissures with a colourless substance, such as oil, wax or artificial resin, has been common in the gemstone trade for many decades, if not centuries. The aim of this treatment
is to reduce the visibility of fissures, thereby enhancing the gemstone’s visual appearance. Although this treatment is well known for emeralds, it may be and often is applied to all sorts of gemstones containing visible fissures. This has been repeatedly reported by SSEF (see, for example, SSEF Facette No. 23 (2017), page 16; No. 24 (2018), pages 14–15).
A recently submitted 18 ct Burmese spinel (Figure 1) is the perfect example to demonstrate the effect of fissure-filling treatment on a gemstone. Upon examination, numerous dendritic patterns were observed in the fissures under a microscope (Figure 2), indicating the presence of a small quantity of oil within the spinel’s fissures, which effectively reduced the visibility of the fissures within the stone. This became evident when the spinel was resubmitted after thorough cleaning by the client, revealing major fissures in the stone’s centre.
