Re: A question of paper
You may get some information from
"The Art Forger's Handbook" by Eric Hebborn, published by Cassell about 10 or 15 years ago.
Hebborn was a self confessed art forger, born in London, and later moved to Rome. He specialised in forging drawings and sketches from the Renaissance period up to the 20th century. His technique was to buy antiquarian books from the period he was forging, and draw on the blank front and end papers. He used a simple home made ink (Ox gall or Oak gall ?) which was used in the middle ages. This meant that his materials resembled those used by the original artists, and chemical analysis would be unabled to tell the difference.
I should imagine both Durer and Turner would have painted watercolours on paper. You should be able to get more info on Turner by finding a good biography.