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One thing I find interesting about paper is that wetting and drying it turns it uneven. Even when drying it under a press.

And then another ridiculous process not involving paper, but super cool nonetheless is creating a flat surface by grinding 3 not-flat objects against each other in round-robin manner.

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Three negatively curved surfaces (saddles) mate despite not being flat. You need to rotate the surfaces also when lapping. (See the famous Robrenz video)

I did not know this, very interesting.

I think wetting and drying of paper is a bit like heat treatment of steel. The fibres find a new local minimum stable position, prompted by the swelling and the shrinking.

Exactly. They were initially rolled, not merely pressed, which implies a longitudinal strain during the pressing moment.

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