Dharmendra, There are many types of topaz in the world with different
trace elements contained within. These trace elements act to
stabilize and affect the color of treated topaz. All these types of
topaz are not equally suitable to become the irradiated blue topaz.
There are also different sources and intensities of irradiation
available - not all equal. You have the very common Cobalt 60 used
in sterilization plants and hospitals, expensive Linear Accelerators
and government controlled Nuclear Reactors.
I think all topaz will turn brown with irradiation. Much of this
material is not stable and has what is known as
Brown-Fading-Color-Center. It will revert to a colorless state in
Only some topaz will turn blue or blue-brown. In this material the
brown can be driven off with heat leaving only the stable blue
Then there are different types of treatments that this material can
be subjected to... i.e. Linear Accelerator, or Nuclear Reactor.
These different treatments result in different colors of blue in
Most likely you have Brown-Fading-Color-Center Topaz which was
subjected to Cobalt 60 treatment.
For more info. refer to Kurt Nassau's book - Gemstone Enhancement -