Set of French envelopes almost identical from 1960s with same stamp, same addressee...

Advertising blotter of the French Francorusse entremets brand from 1950s

Blotting paper (or blotter) is a porous paper capable of absorbing a small amount of liquid. It was mainly used to dry the writing when it was written in ink with a pen: ink can be deposited irregularly and dried slowly could cause stains and maculatures, the use of blotting was often necessary.