The most common and most likely answer to this crossword clue is the 3 plus 6 letter word BAS RELIEF
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More clues leading to the result BAS RELIEF
Buddy explains!

The straight part
We know that "Sculpture technique" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sculpture technique = bas relief.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 BAS RELIEF mean?
BAS RELIEF noun- A low or mostly-flat sculpture which is carved into a wall, or is in the form of a tile mounted flat to a wall, rather than a fully three-dimensional, free-standing figure.
- Refers to any aspect of sculpture which is flat or in the bas relief style.