tax question for diamond sale

[aroser]

I recently sold a diamond and now my accountant is trying to figure out how it fits into my tax return; basically what was the stone worth 10 years ago vs what I sold it for. How would I go about doing that? It is a round brilliant, 5.35 carat, color K, clarity VS2, cut is very good.

 

[baby monster]

Your basis is what you paid for the stone. Do you have paperwork to prove it?