Mural painting (6)
I believe the answer is:
fresco
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">mural painting</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for fresco that I've seen before include "Painting done in wet plaster" , "Mode of wall painting" , "Painting using watercolours on plaster" , "Watercolour done on wet plaster" , "Wall-painting" .)