Key on ring beneath father’s painting (6)
I believe the answer is:
fresco
'painting' is the definition.
(I know that Fresco is a type of painting)
'key on ring beneath father's' is the wordplay.
'key' becomes 'esc' ('Escape' key on a computer keyboard).
'on' says to put letters next to each other (in a down clue, letters appear on others).
'ring' becomes 'O' (O is the shape of a ring).
'beneath' means one lot of letters go next to another (in a down clue, some letters go beneath others).
'father' becomes 'fr' (abbreviation as in a priest's title).
'esc' next to 'o' is 'esco'.
'esco' after 'fr' is 'FRESCO'.
(Other definitions for fresco that I've seen before include "Mode of wall painting" , "Watercolour done on wet plaster" , "Mural painted on wet plaster" , "Painting style" , "Picture painted on wall or ceiling before plaster is dry" .)