The beryllium diffused sapphire struck fear into the heart of the industry for several years as it was the first time that a major gemstone could be diffusion treated using a process that totally permeated the gemstone. Previous diffusion efforts with sapphire had resulted in only surface diffusion of colour onto the stone. But with the advent of the Be treatment the old methods of identification went out the window. Fortunately the Be treatment imparts classic and diagnostic features that can be used to positively identify the sapphire.
The main tool is magnification. The internal characteristics left behind by the diffusion process creates inclusions that are unlike anything natural to the trained eye. These include blue halos which are the result of residual iron and titanium reforming their bond around pre-existing crystals. The re-bonding of the Fe/Ti elements causes the blue halos to be present in sapphires that otherwise are yellow, orange, and a variety of other colours. Also, the presence and formation of unusually large fingerprint type inclusions is another of the Be process.
GIC GemLab is the first and the only gem laboratory in Sri lanka to equip a LIBS Laser Induced Breakdown Spectroscopy) for Beryllium diffused sapphires. This breakthrough should keep the GIC ahead of those seeking to pass off beryllium-treated rubies and sapphires as something else.
The LIBS set-up consists of several components. The high powered laser that ablates or vaporizes a tiny volume of the surface of the sample. The ablated area is usually just barely visible with a microscope under 10x and is usually about 50 micrometers in diameter. A microscope with video camera is often used as an aid in positioning the sample.
When the laser impacts the sample it vaporizes a minute quantity into a high temperature plasma cloud that reached 50,000° C in the centre and is about 5,000°C at the edges. The excited elements in the sample emit light at specific wavelengths that are in turn measured by a series of six or seven sensitive spectrometers that measure the wavelengths from 200-900nm. The results are graphically displayed by computer.
The limits of detection for Be are nominally about 3 ppm under ideal circumstances, which is fairly close to the minimum required for coloration in corundum.
