Comparative form of blotty; more blotty or blotched than something else.
From blotty (adjective form, less common than blotchy) plus -er comparative suffix, showing an alternative form that rarely gets used.
Blottier is technically correct but almost nobody uses it because 'blotchier' sounds more natural—this shows how English speakers prefer some word formations over others, even when both are grammatically valid.
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