The most common and most likely answer to this crossword clue is the 14 letter word FORESHORTENING
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Buddy explains!

The straight part
We know that "artistic effect" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case artistic effect = foreshortening.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does FORESHORTENING mean?
FORESHORTENING verb- To render the image of an object such that it appears to be receding in space as it is perceived visually.
- To abridge, reduce, contract.
- To make shorter.
- A technique for creating the appearance that the object of a drawing is extending into space by shortening the lines with which that object is drawn.
- A similar contracted appearance in film or photography, etc.