Chipping of Emeralds

Figure 1: Before and after photos of an emerald with an evident (cleaned) fissure in the upper left corner, which spontaneously chipped at SSEF during normal testing procedures. Photo: V. Lanzafame, SSEF

by Dr. M. S. Krzemnicki first published in Facette 25 (February 2019)

Emerald fissure filling and issues related to this treatment and its decomposition and cleaning are a constant issue in the lab and in the trade. With the current market-trend to offer emeralds which are either filled only by oil or which show no indications of clarity modification at all, a rather large number of emeralds formerly treated with artificial resin in fissures are cleaned, using strong acidic solutions.

This cleaning process, often supported by mechanical tumbling and ultrasonic cleaning may result in chipping or even cracking of pre-existing fissures within the emerald at any time afterwards (Figure 1).

We have recently come across a few cases, when small chipping actually happened during normal handling procedures in the laboratory. This is very unpleasant for all involved parties, as it requires repolishing at least. We therefore would like to remind the trade that emeralds are rather brittle and fragile especially when exposed to such cleaning processes. This is especially the case for Colombian emeralds, as they often contain small fissures due to specific geological conditions and mining methods (Figure 2). Any cleaning (especially when applied multiple times with strong acids) always bears the risk to cause chipping of the emerald, whether just after cleaning, during lab testing, when mounted in jewellery, or even worse after selling the emerald to a final consumer.

Figure 2: Journey of a Colombian emerald of 8.1 ct in three stages: Untreated (left) revealing apparent fissures in the stone, with moderate amount of artificial resin in fissures (middle, perfectly hiding most of these fissures, and after partly cleaning but with still with minor artificial resin in fissures (right). Photo: M.S. Krzemnicki, SSEF