LP
Led Zeppelin II
USA, 1-Song 10″ (45-2690) Acetate

Here is 10″ acetate used for the 7-inch single release of Whole Lotta Love/Living Loving Maid (45-2690)

Acetates. also known in the industry as lacquers are the first step in the physical manufacturing of a record. They are usually one-sided, lacquer-coated aluminum discs and heavier than commercial records. 

Acetates are made for two purposes, to evaluate a recording and its suitability for pressing records and to use in the production of the finished product itself. There are never many acetates made during production, usually no more than 10, which make these pressings very sought after.