The most common and most likely answer to this crossword clue is the 7 letter word IMPASTO
I've seen this crossword clue in The Guardian
I
M
P
A
S
T
O
More clues leading to the result IMPASTO
- Here's what I think about former style of painting
- One too old for probing instant painting technique
- I’ve reached “P for Paint”?
- Terror regarding painting technique
- The writer's quiet on the subject of artistic technique
- I am beyond getting Oscar for picture-making skill
- Ma’s top I replaced, putting on thick coat
- One’s beginning to paint, respecting such a technique
- Thick coat finished in one second
- Very thick painter uses this progress report on learning alphabet?
Buddy explains!

The straight part
We know that "Thick coat" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case thick coat = impasto.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 IMPASTO mean?
IMPASTO noun- The use of a thick-bodied paint to create sizable peaks and crests in an image.
- To paint in thick-bodied paint; to paint in impasto style