The most common and most likely answer to this crossword clue is the 6 letter word NIELLO
N
I
E
L
L
O
More clues leading to the result NIELLO
- Famous mistress hugging one with love to make impression?
- Black alloy, cool, turned yellow when exposed
- Engraving that is inspired by last of Jackson Pollock’s three pivotal pieces
- Compound used in ornamental engraving can make one ill
- Black compound formed by iron crust turning yellow on the inside
- Lionel adapted ornamental engraving
Buddy explains!

The straight part
We know that "impression" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case impression = niello.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 NIELLO mean?
NIELLO noun- Any of various black metal alloys, made of sulphur with copper, silver or lead, used to create decorative designs on other metals.
- An impression on paper taken from the engraved or incised surface before the niello alloy has been inlaid.
- To decorate (a surface) using this technique.