Gem treatments - Lattice Diffusion

Lattice diffusion

– the penetration of certain elements into the atomic lattice of a gemstone during heat treatment, with the objective of changing or accentuating its color.

1. The most commonly encountered diffused gems include:

Corundum (ruby and sapphire) – while experimentation during the 1980s concentrated on diffusion of titanium and chromium (which are coloring agents in corundum), the ability to fully penetrate the stone with color met with little success. In 2003, very strongly colored sapphires began to appear in the market, and diffusion was again suspected. It was found that it was diffusion — but of a new element: beryllium. Beryllium which has a much smaller atom than titanium or chromium, was able to diffuse all the way through a sapphire; even large sapphires, successfully changing their color. It was soon found that the color of rubies could be accentuated as well using this treatment process.

Untreated sapphires on the left (first group), diffused and unpolished (second group), over polished needing re-diffusing (third group), and successful diffusion treatment (fourth group).

Feldspar – Varieties of feldspar, notably andesine and labradorite were found to be receptive to the diffusion of copper, completely altering their color.

Untreated rough feldspar (left) and various treated feldspar (right)

Other materials – There have been reports of diffusion to cause color alterations in both tourmaline and tsavorite (a variety of garnet) but the claims have not been substantiated.

2. Durability factors – The treatment is considered permanent.

3. Detectability – Extremely difficult to detect with certainty in many instances—and if so, only by qualified laboratories.

4. Encountered in the trade – Diffusion treated corundum is widespread in the trade.

5. Special care requirements – There are no special care requirements for diffusion treated corundum or feldspar.

 

Source: Robert Weldon, www.gia.edu

To learn more about gem treatments see also:

- An introduction to Gem treatments

- Gem treatments - Bleaching

- Gem treatments - Surface Coating

- Gem treatments - Laser Drilling

- Gem treatments - Irradiation

- Gem treatments- Impregnation

- Gem treatments - High Pressure, High Temperature (HPHT)

- Gem treatments - Heat treatment

- Gem treatments - Fracture or Cavity Filling

- Gem treatments - Dyeing