sepia ink and watercolour over pencil.
Cotman never visited Venice only getting as far as Normandy.
He would seen this image in prints or was inspired by another artist's work. It has similarities with Samuel Prout's work .
Probably painted during the latter part of his career ,some of the buildings and sky are unfinished.
Cotman often used sepia ink for the outlines of his watercolours, this would become more obscured the more he worked up the watercolour.