Although pink and a reddish-orange color known as imperial are the most valuable colors of topaz, this gemstone variety is now most often seen on the market in a blue color, thanks to a new irradiation enhancement process for colorless topaz developed in the 1970’s.
The world’s most famous topaz, the huge Braganza set in the Portuguese Crown, was originally thought to be a diamond.
Topaz is the traditional US birthstone for November. Blue topaz is considered an alternate US birthstone for December.
Topaz can be the amber gold of fine cognac or the blush of a peach and all the beautiful warm browns and oranges in between.
The most valuable topaz is more red than yellow from pale pink to a “sherry” red. Imperial topaz is also highly valued. Yellow to brown topaz is more affordable.
The strong icy blue color of blue topaz is created by exposing colorless topaz to low levels of irradiation and heat. Lighter colors are created by electrons and the darker blue known as London or Super blue is created by neutrons. Treated topaz has no harmful radiation levels. Blue topaz is among the most affordable color gemstones.
Heat treatment is sometimes used to change yellowish topaz to pink.
Surface coatings and diffusion treatments can be used to create other colors. These surface coatings may come off in time with normal wear.
Topaz is most often found in a scissor cut, a rectangular gem shape with curved sides that have triangular facets. Ovals, cushions and emerald shaped are also available.
Because blue topaz is readily available and affordable, it can be found in a wide variety of shapes and sizes, including unusual shapes.
Topaz has a high hardness of 8 on the Mohs scale, but it isn’t tough. Like a diamond, it has a pronounced cleavage: a single blow can break it in half so it should be protected from knocks.
The treated color of blue topaz is stable and permanent and does not require special care.
Clean topaz with mild dish soap in warm water: use a soft toothbrush to gently scrub under or behind the gemstone where dust and dirt can collect.
Some information from the GIA web site.