Set into a surface (6)
I believe the answer is:
inlaid
'set into a surface' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for inlaid that I've seen before include "Decorated with embedded elements" , "Set into surface ornamentally" , "Studded" , "(Of decorative items) embedded" , "Decorated with embedded materials" .)