What does the cryptic crossword clue "I give black marks for going on the lash (7)" mean?

The definition is "I give black marks for going on the lash". The wordplay uses a cryptic definition. Cryptic definition The answer is MASCARA.

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

Guardian Cryptic #29375 | 10 Across | 2024-05-06 flower