The present participle of blotch; creating blotches or irregular spots on a surface.
From blotch (a dark discolored spot) plus -ing, the suffix that creates present participles and gerunds from verbs.
Blotching can be accidental (like spilling ink) or intentional (like an artist using dry-brush technique), and the same word works for both because English verb forms don't care about your intentions.
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