"Oil Slick" On CGC Inner Well

[crazyhips]

I have a few slabbed books that appear to have a rainbow colored oily residue on the inner well. Any ideas as to what this is?

[BlowUpTheMoon]

Static cling - nothing to worry about.

[Aces]

Static cling - nothing to worry about.

Plastics are largely made from oil.

(thumbs u

[towards2112]

Static cling - nothing to worry about.

Plastics are largely made from oil.

(thumbs u

 

Crack it out and have it pressed, then there won't be so much pressure on the

inner well causing it to come in contact with the outter shell. (thumbs u

[rodan57]

Sometimes you can see the same thing on a tilted blank CD or DVD.

[Davenport]

I have a few slabbed books that appear to have a rainbow colored oily residue on the inner well. Any ideas as to what this is?

I pretty sure it's an optical effect knowns as "Newton's rings"

 

"The rings appear when there’s a tiny air gap between two pieces of clear material. Light rays encounter destructive interference if the gap is of a certain size relative to the wavelength, resulting in the effect. It’s most pronounced if a convex lens is pressed up against a perfectly flat glass surface."