ink

He thought so because lemon juice works as invisible ink on a piece of paper.

So three years, and a bunch of ink in an aquarium?

Or the envelope got a bit damp, and the ink blurred and ran?

Printing manufacturers stole the razor-and-blades business model from Gillette, selling printers cheap but ink expensive.

I used to think that a tattoo machine came to a single needle point and it injected ink under the skin.

The postal service sends the picture of the envelope here to the Remote Encoding Center, the REC, in Salt Lake City, Utah, and it's the job of the folks here to turn scrawl and blurred ink into actual addresses.