Bubbles in brownish epoxy resin in an emerald from Colombia, darkfield illumination
Micrographs

Emerald from Colombia whose cracks are filled with epoxy resin

 
Spherical gas bubbles can be observed in emeralds whose cracks are filled with epoxy resin. However, so that the surface tension can be expressed freely and give an almost round morphology to a bubble, we need space around it, which indicates to us that we are obviously in the presence of a cavity in this place.
 
Above, one can observe cracks containing yellowed epoxies. The appearance of this yellow color (which can turn brown over time) is due to the formation of aromatic rings. This is one of the many problems associated with using epoxy resin to fill cracks in emeralds. Cedar oil also has drawbacks, which shows us that it is important to pay attention to the degree of importance of transparency enhancement, mentioned in reports.