Blue Topaz Treatment

Blue topaz is made from white topaz through irradiation, not heat
treatment. 

Actually, blue topaz often gets its color from both irradiation
and heat treatment: Irradiation first, heat second. And it
doesn’t always start as white topaz. References:

http://www.yourgemologist.com/irradiation.html
http://www.geology.wisc.edu/~jill/Lect10.html

http://www.professionaljeweler.com/archives/articles/1999/mar99/0399fys2.ht
ml

Beth