Dartek reaction to molded acrylic

I am working with a series of works made out of thermoformed PETG plastic. They have been wrapped in dartek and boxed for about six months. Upon opening I observed a marbling texture, similar to the texture of the dartek, seemingly etched into the outside surface of the PETG.

Wondering if anyone has had experience with dartek leaving a residue on formed plastics?

Have experimented with Novus cleaning solution to remove the residue with little luck.

Any suggestions for cleaning techniques, or more appropriate storage solutions for thermoformed acrylic would be much appreciated!

(see below for image. residue most visible in bottom portion of the image, in the reflection of the light. note that the color pigment is on the under or backside of the piece, so the dartek is only in contact with the PETG plastic on the outside, not the pigment on the inside)

http://www.paccin.org/attachment.php...tid=2222&stc=1