It has to do with the paper itself. I know that for single transfer carbons
some papers clear in no time while others take forever, requiring
bisulfite, etc.
There is no need for constant running water. I used to keep carbon prints
slightly submerged, with a fiberglass screen or some other plastic object
on the back. A few changes of water over the following 1 to 2 hours would
do the trick nicely.
Luis Nadeau
awef6t@mi.net
Fredericton, New Brunswick, Canada