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Newton's rings

Newton's rings is a flaw that can occur in a photograph or transparency that had grease on it whilst it was being scanned. The visual effect is similar to that of oil poured on water.

Non-printing blue

A blue pencil that can be used to mark up artwork or mechanicals. Useful, because it will not be picked up on graphic arts films. Also known under a number of other names such as, non-repro blue, drop-out blue and simply blue pencil.