Polish conjuror finally involved in perfect disappearance (4,7)
I believe the answer is:
nail varnish
'polish' is the definition.
'conjuror finally involved in perfect disappearance' is the wordplay.
'finally' indicates one should take the final letters.
'involved in' means one lot of letters goes inside another.
'perfect' becomes 'nail' (as a verb - to nail it).
'disappearance' becomes 'vanish'.
The last letter of 'conjuror' is 'r'.
'nail'+'vanish'='nailvanish'
'r' going inside 'nailvanish' is 'NAIL-VARNISH'.
(Other definitions for nail varnish that I've seen before include "digital enhancement" , "Lacquer at one's fingertips" , "Shiny fluid applied to the tips of one's digits" , "Make-up for fingers and toes" , "Manicurist's cosmetic lacquer" .)