Info wanted re London blue topaz

[laurenk]

Hello all
A friend of mine is looking for a 3 carat London blue topaz. I told her I would try to gauge what to look for and what to avoid from this wonderful page. Is "London blue" simply a shade of blue? Are topaz expensive? Any pointers would be great!

 

[chrono]

Topaz is a natural gemstone but to get it "London Blue", it is irradiated to become that colour. Rest assured, the treatment is permanent, stable and safe by the time the stone is sold to the public. Yes, blue topaz is very cheap and plentiful, so you should get one that is very well cut because you can afford to be choosy.

They are about $2/ct here.
http://www.diamondexpert.com/diamonds/dbs.cgi?sf=detg.setup.cgi&active=active&stock=TP01856&submit_search=1

 

[T L]

Just beware of coated topaz, as the coating is not always stable. Modern electron bombardment treatment is more safe than neutron bombardment. Always buy from a reputable vendor who isn't selling anything coated or radioactive.

I think, but don't quote me on this, but London blues are neutron bombarded, so I would stick with lighter stones, like Swiss blue, to be on the safe side. They may also be coated as the nuclear regulatory commission did test these stones, and the darker blues might need coating to get that darker color. Beware of old stones, as in pre-worn rings from the 80's, as they may be more radioactive. I would buy a new Swiss blue from a reputable vendor. London blues are also pretty inky looking and not as attractive IMO.

For science geeks like me, here's an article on the radioactive decay of blue topaz from the GIA.

http://www.gia.edu/cs/Satellite?blobcol=gfile&blobheader=application%2Fpdf&blobheadername1=Content-Disposition&blobheadername2=MDT-Type&blobheadername3=Content-Type&blobheadervalue1=attachment%3B+filename%3DThe-Radioactive-Decay-Pattern-of-Blue-Topaz-Treated-by-Neutron-Irradiation&blobheadervalue2=abinary%3B+charset%3DUTF-8&blobheadervalue3=application%2Funknown&blobkey=id&blobtable=GIA_DocumentFile&blobwhere=1355958113692&ssbinary=true

 

[RandG]

Hello all
A friend of mine is looking for a 3 carat London blue topaz. I told her I would try to gauge what to look for and what to avoid from this wonderful page. Is "London blue" simply a shade of blue? Are topaz expensive? Any pointers would be great!

Here's an example mounted. The mounting as scrap is worth more than the stone...

 

[dk168]

My understanding of London Blue is a darker blue than the more vivid and lighter Swiss Blue Topaz, and it is the latter that I like.

The pics posted above is what I would describe as a typical London Blue Topaz.

DK

 

[laurenk]

Thank you also much!!! That info is excellent - I appreciate it so much.