Timeless works created in this medium (4)

I believe the answer is:

oils

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'timeless works' is the definition.
The answer and definition can be both man-made objects as well as being plural nouns.
Maybe you can see a link between them that I don't see?

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for oils that I've seen before include "Reduces friction" , "7's paint medium" , "Soil, oddly, used by painters" , "Olive and sesame, for instance" , "Lubricates; paints" .)

I've seen this clue in The Irish Times.

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