I give black marks for going on the lash (7)

I believe the answer is:

mascara

I'm a little stuck... Click here to teach me more about this clue!

'lash' is the definition.
The definition and answer can be both man-made objects as well as being singular 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 mascara that I've seen before include "Make-up item" , "Eyelash darkener" , "Eyelash make-up" , "that accentuates lashes" , "Makeup used to darken and thicken the eye lashes" .)

I've seen this clue in The Guardian.

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