Unusual Composite Ruby

(via ICA Lab Alert, No.2, June 1987) AIGS writes:

During June of 1987, a very unusual composite ruby/synthetic ruby was brought in to the lab of AIGS for testing. It consisted of a piece of Verneuil synthetic ruby to which had been joined at the edge a smaller chunk of natural Burmese ruby. The whole stone was then faceted, concealing the join.

Two features are unusual about this stone. First of all, what appears to be glass has been used to join the two together. Gas bubbles were found in the glass area. Secondly, the edges of both the natural and synthetic areas were irregular. The use of glass to join the two together made this possible, as the glass-filled in the irregular surfaces. The entire stone showed signs of heat treatment, with induced fingerprints present in the synthetic section.

Detection
With the loupe or naked eye this stone could fool many people as the join looks like a crack and the natural area contained a large cloud of silk. However, immersion or overhead lighting will reveal the different luster of the glass join in the microscope. In addition, the synthetic portion displays curved striae and gas bubbles, as well as the induced fingerprints. The stone was purposely cut ‘native’ to imitate the appearance of a ruby just brought out from Burma.