The most common and most likely answer to this crossword clue is the 12 letter word SANDPAPERING
I've seen this crossword clue in Financial Times
S
A
N
D
P
A
P
E
R
I
N
G
Buddy explains!
The straight part
We know that "Polishing" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case polishing = sandpapering.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 SANDPAPERING mean?
SANDPAPERING verb- To polish or grind (a surface) with or as if with sandpaper.
- An application of sandpaper.