One of the two conditions needed for משקה הבא לאוכל (squeezing liquids onto solids).
Some more important examples of temporary writing, which come up on a weekly shabbos.
Is One Allowed to Trap a Bee, Hornet, Wasp, etc. If It Is Bothering People?;
The Proper Procedure for Checking One's Blood on Shabbos (e.g., for Diabetics);