What are Newton rings on a CGC slab?
Published Sep 14, 2026 · Updated Oct 11, 2026 · 1 min read
Short answerNewton rings are the faint rainbow or oily-looking patterns you sometimes see through the front of a slab where the inner well touches the comic's cover. They are an optical effect caused by two smooth surfaces pressed close together, not damage to the book, and they do not affect the grade. They are cosmetic and often disappear if the book is reholdered.
What causes them
When two very smooth surfaces — the plastic inner well and a glossy cover — sit within a fraction of a millimetre of each other, light reflecting from both surfaces interferes and produces concentric coloured bands, the same effect you see in a thin film of oil on water. The effect was described by Isaac Newton, hence the name.
Are they a problem?
- For the book: no. Nothing is touching the paper in a harmful way and the cover is not marked.
- For the grade: no. Graders assess the book, not the holder, and the rings were not there when it was graded.
- For display: sometimes. They can be distracting on a dark or glossy modern cover.
How to get rid of them
The rings depend on the exact contact between well and cover, so they can appear or vanish with temperature, pressure or handling. If they bother you, CGC's reholder service replaces the case, usually without the rings — although there is no guarantee they will not return. Do not attempt to open or flex the case.
Related cosmetic issues
- Scuffs and scratches on the outer case — again cosmetic, fixed by reholdering.
- A book shifted inside the well — occasionally seen after rough shipping; reholdering re-seats it.
None of these change the grade, but when buying at a distance ask for a photo taken at an angle so you can see the case as well as the book.
Written by the Rare Comics Collectors grading team. Spotted an error or have a question this guide does not answer? Tell us.