Treated Topaz

In most respects, topaz is an excellent gem. Its one real defect is an easy cleavage parallel to the basal plane. As a result, durability is fair, even though the hardness is eight on the Moh’s scale. There is a clear distinction in quality and value between the different colors in topaz.

The color of most pink topaz is produced by heat treatment of sherry brown material. Such stones are termed pinked or fired. The resulting color is stable. Over 99% of all blue topaz sold today is the product of treatment. Pale blue or colorless material is irradiated, turning it brown. Then it is heat treated to induce a handsome blue (stable) or green (unstable) color. Depending upon the type of treatment used, light to medium aquamarine-like blue is produced, as well as deep 'Super' and 'Swiss' blues not met with in nature. Also note that a fair percentage of brown topaz (and possibly other colors) has resulted from natural irradiation. Much brown topaz fades on exposure to sunlight.

Coated topaz is becoming popular in the gem industry because of its availability in a wide variety of colors such as blue to green, pink, orange, and in multi-colors. The stones are attractive but most colors are produced by dyeing or sputtering method, and can be easily removed. Some of the coatings, especially pink deceived many experts because the coatings were on the pavilion. In the gem testing laboratory analytical tests are usually performed on the table, but when analyzed from the side the coatings are easily detected.

There is another type that produces green and blue colors, which is perceived to be a different type of diffusion process than simple coating. The colors may not be that easy to remove by scratching or exposure to acetone, but immersion in hydrofluoric acid may cause discoloration. The experts believe that green-coated topaz by immersion in hydrochloric acid and hydrofluoric acid for an hour or more may dissolve the coating. The result (s) from laboratory experiments and proper analysis suggests that diffusion of chemical elements into the topaz may not have occurred, instead some chemical reaction between the topaz and coating may have taken place to prevent the easy removal of colors. Gem treatment identification is a logical process of deduction or alternatively of elimination. Obviously the first step is to look at the stone and note its color and other visually determinable properties followed by more complex and time consuming steps. With analytical instruments, color causing elements can be easily detected with reference samples and data without any destructive tests.

As usual, the colored stone industry will always encounter new and more durable surface coating techniques because consumers want new colors at an affordable price. If in doubt always consult a reputed gem testing laboratory.