Note: this was originally posted on page 15 of a thread in Comics General on August 31st. We're creating it as an announcement to make it easier to find.
The “rainbow effect” or “Newton rings” are a normal occurrence when two different plastics (which have different refractive indexes) are placed together. It’s what you sometimes see on a smartphone screen protector or on the edges of an LCD screen.
The rainbow effect has been seen in CGC holders since our first-generation holder was introduced nearly 20 years ago. This is a result of the inner sleeve (which holds the book) contacting the hard-plastic outer shell; the two different plastics have different refractive indexes and that sometimes creates a rainbow effect when they come into contact. A minor rainbow effect has always been within our tolerance. If anyone feels that they have a book that exhibits an extreme rainbow effect, however, we encourage you to contact our Customer Service at email@example.com.
Behind the scenes, we are constantly working to improve the CGC holder. Most recently, we have made a slight modification to the inner dimensions of our standard holder to accommodate the increasing variety of comic book sizes and paper stocks. In our testing, this minor modification was also shown to reduce the presence of the rainbow effect for many books. We did not want to share our findings until our thorough testing was complete, and now that it is, we are pleased to report that these modified holders have been fully integrated into our encapsulation process with very positive results.
CGC continues to research enhancements to its holders, including ones that may further reduce the rainbow effect, and we will keep you updated with any noteworthy developments.
Example of extreme rainbow effect: