"Blot something" vs. "Blot dry something"

A blot (noun) is a stain of ink (or similar). You would get blots when writing with an old style "dipping" pen, which tends to splash ink on the page.

As a verb "to blot" there are several different meanings

1. To stain with ink, or to smudge wet ink. (and hence figuratively, to do something badly)
2. To dry ink using absorbent paper, to prevent blots.
3. To hide something by convering it with ink (in phrase "blot out", also figurative)

You can say "blot dry" to emphasise that it is the second meaning.

The verb "blot" is a contranym: it has two meanings that are opposite each other. You use context to understand which meaning is intended.

Nowadays "blot" is nearly always figurative since people don't use dip-pens very often.