Writing instrument could make plain blot (9)

I believe the answer is:

ballpoint

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'writing instrument' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps you can see an association between them that I can't see?

'make plain blot' is the wordplay.
'make' indicates an anagram.
'plain'+'blot'='plainblot'
'plainblot' anagrammed gives 'BALLPOINT'.

'could' acts as a link.

Can you help me to learn more?

(Other definitions for ballpoint that I've seen before include "Writer" , "Biro" , "Type of pen" .)

I've seen this clue in The Irish Independent.

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