Clarity Question

[JasonL]

I asked this the other day in the reply to a post, but I wanted to ask again.

I was told by a jeweler that when a diamond is dirty (ex. oil from hands) that inclusions looking through the table become more apparent. Any truth to that or was he just trying to make me go higher in clarity?

 

[Spyder]

It seems to me that if the outside of the diamond is dirty, it will make it harder to see anything inside.

If you want to see the inclusions, be sure to thoroughly clean the outside of the diamond first.

If he was talking about surface graining, then it might become more noticable when dirt gets into the grooves.

 

[pyramid]

From my experience he is telling the truth. My sister has a pear shaped diamond which is G in colour and SI1 in clarity. It has a very small black carbon spot just below and to the side of the table. When the stone is dirty, she only gets it cleaned at the jeweller about every 3 months, I can see the black spot when looking close because I know where to look, this is with the ring still on her hand e.g. when we are sitting across from each other at a very small dining table. When the stone is clean I cannot see the black spot. I have very good eyesight for seeing inclusions but the sparkle when the stone is clean hides it from view. It is a very very tiny spot so anyone else would not see it but I do as I know where to look and that it is there.

 

[Richard Sherwood]

He's correct. The refractive index of the oil from your hands is higher than that of air, which makes it easier to see "into" the diamond if it has a surface coating of skin oil.

This is basically the same principle that's used in "immersing" a stone in a liquid with a higher refractive index than air to more easily view the inclusions. Air has a refractive index of 1.00, while water is 1.33, cedar wood oil is 1.51, cinnamon oil 1.59, cassia oil 1.60 and methylene iodide (gemologist's favorite) is 1.742. (Diamond is 2.42)

The refractive index of skin oil probably falls between the 1.33 of water and the 1.51 of cedar wood oil.

The second aspect is that the oil dulls the brilliance of the stone, which might make it easier to see the inclusions.