The most common and most likely answer to this crossword clue is the 7 plus 6 letter word GALLOWS HUMOUR
G
A
L
L
O
W
S
H
U
M
O
U
R
Buddy explains!
The straight part
We know that "dark material" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case dark material = gallows humour.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.