Amateur mural ultimately delineated with felt-tip pen (7)

I haven't cracked this one yet — but the brilliant team at Times for the Times have:

{mura}L [ultimately] contained by [delineated with] DABBER (felt-tip pen). I didn’t know this, but Collins has: dabber – a felt-tip pen with a very broad writing point, used esp by bingo players to cancel numbers on their cards. ‘Delineate’ can mean to set boundaries, so I guess that justifies ‘delineated’  as a containment indicator.