"Oil slick" appearance on crown

[Wwoofa]

Hi,
I have a cut stone (garnet) with an "oily" appearance on the crown.  What causes that?  I was told that it is perhaps caused by having too much diamond powder or oil on the lap?  I assume the only way to remove it would be to repolish it?  Is that right?
Regards, Paul

[mehoose]

Woofa, hang ten before repolishing. I'm sure I read somewhere it's an optical thing. Will try to find it for you.

[Bluey Zarzoff]

Was just wondering if it is perhaps silk in the stone.

Have heard of the the possible presence of silk in Garnets.

[mehoose]

ok, have a read here Woofa, Gearloose pointed me in the right direction for the link. Is this what you see?

http://www.gemologyonline.com/Forum/phpBB2/viewtopic.php?f=8&t=3592&start=3825

[jad]

Aside from the oily reference, those cuts on that link are amazing. Wow! 

JAD

[mehoose]

Not bad eh! 

[Wwoofa]

Thanks Mehoose, 
It does look like "Newton Rings".  Seems to happen when the stone contacts the lid of the clear display box it's in.  I moved it around a bit and the rings disappear ... also if I wipe the inside of the lid with a cleaning cloth then the rings come back.  Very interesting.
Regards, Paul

[mehoose]

Come to think of it, a seller at last years gemboree tried removing the same thing when I said,it was a shame the angle showed oil. LOL, even she didn't know what it was cos it didn't budge with further cleaning. 
Did you read the article at the link in Gearloose's post on the same page?
Interesting info, good to know.

[Wwoofa]

Yep I read that ... it's very interesting.  It's the type of thing that OCD'er would have nightmares about ... I think my therapist would advise me to avoid "interferometers"

[mehoose]

LOL

[Blocker]

Newton Rings are the curse of photographers particularly back in the days when I spent time in the dark room.  Its the relection of light between 2 internal surfaces (usually in the lens) so I suppose you will get it between gemstone surfaces. It probably depends of the relective characteristics of any particular gemstone and how it is cut or the angles of surfaces relative each other.