All, Normally diffused sapphires can be identified by immersing the
stones and looking for the spiderweb effect caused by repolishing.
These stones did not show any spiderweb effect under normal
observation. Two clues in the parcel alerted the dealer. First the
parcel contained multiple stones of 1-5 carats that were almost
identical in color. All high color Ceylon Blue. Second the price
was almost 1/2 of what these stones should have cost. Only very
close inspection under immersed and magnified conditions brought to
light the minor thickness variations in the polish on the facets.
Close examination showed the effect in multiple areas on each stone.
I have heard that stones can be diffused to a depth of 2mm. That is
more than enough room for a good cutter to repolish and leave very
little evidence of the process. Buyer beware.