Was there to observe material (5)

I believe the answer is:

satin

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'material' is the definition.
(satin is a kind of material)

I don't understand how the remainder of the clue works.

(Other definitions for satin that I've seen before include "Shiny solk" , "Material with glossy front and dull back" , "Rich cloth" , "Silk fabric" , "Saint (anag.)" .)

I've seen this clue in The Guardian.

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