How do I solve 19 down in Daily Telegraph Cryptic 31244?

Question

Accepted Answer

19 down reads "Outstanding art gallery film material" (7 letters); the answer is ACETATE. It's a charade: the answer breaks into parts in clue order, each part clued by a word or short phrase. No indicators needed; watch for standard abbreviations (RA = artist, US = American, IN = at home) and short synonyms. The full step-by-step breakdown is on this page.

Outstanding art gallery film material (7)

19D — Outstanding art gallery film material (7) — ACETATE