Grain lines are not treated with anything. The use of fillers in diamonds to alter the appearance of very specific types of cleavages or fractures is quite limited in real world use because it is a treatment that often does not work and is held in such low regard by so many dealers and by the semi-informed public. You would be hard pressed to find a really good diamond that had any filler treatment ever.
Do you have a specific stone or circumstance in mind?
I had also read when doing an internet search that thousands of diamonds were treated each year with fracture filling material. Maybe this information I read was incorrect. It was mentioning Koss, Yehuda, Goldman-Oved and Leshem Diamond Co...
Below is the link
http://www.ganoksin.com/borisat/nenam/ajm-diamond-treatments.htm
No Pyramid, the treatment is really quite natural. Just irradiation followed by electron bombardment and then some high pressure heat treatment. None of these needs be declared to the public because they all occur naturally.
The only treatment you need to worry about is hair color dye that can fill the cracks caused by the nuetron bombardment. But this will wash out in hydrogen pyroxide.
So is it correct that Mall Stores do not disclose fracture filling? I found a page from NiceIce saying they found fracture filled diamonds in Mall Chains which said they did not sell fracture filled diamonds. If they do not disclose it is this not illegal?
Pyramid we are having a debate here.
I explained to these North Americans that you would take my sick sense of humour and see the funny side because you are British and all Pom's have a sense of humour.
Is that a true statement?
Or am I just plain offensive?