If I mount multiple images wet, and then do batch scanning , how long, or how do you take advantage of pre mounting a lot of images , BEFORE the fluid, gel becomes problematic.
Can you have a mounted drum sit over a couple of days ? and if so are there any tips on keeping the setup intact and ready to mount to the scanner.
I'm hardly an expert. It'll take a Tim Vitale or equivalent to tell you about the archival aspects of it with any authority. I can only talk with authority about my own experience, not the actual science of it.
Drum scanner mounting fluid is designed for the job. It therefore is harmless to the film, and to the drum. If you clean the film with film cleaner after scanning, it's usually cleaner (and therefore more archival) than when it was first handed to you. If you clean the drum with drum cleaner (*not* film cleaner, which will destroy a drum fairly quickly) you'll get everything off the drum without much problem.
The thing that will limit how long you can keep a drum mount active is the tape -- the scanner mounting fluid dissolves the adhesive. It's pretty slow, but it does happen. That's what drum cleaner is really good for -- cleaning the tape residue off the drum.
So think about what happens when the adhesive is completely dissolved along some part of the tape. There's two things that happen there. First, if you spin it, you can spin out some of the mounting fluid -- might form bubbles which ruin the scan. Second, the fluid can evaporate out that hole, same problem, or you start to develop Newton's Rings in places because of the lack of fluid.
I've never had a problem with letting mounted film sit on the drum for a couple of days. It's useful to do that sometimes -- working too late at night is a recipe for a less-than-your-best scan, so letting a drum sit overnight so you can setup and scan in the morning when you are fresh is sometimes the right thing to do.
The longest I think I had film mounted on a drum is like four days. I was doing some testing, scanning the same film over and over and trying to figure out what was happening. Took several days, then I took a couple of days off (thinking I'd torn down that mount). When I discovered it I torn it down immediately. All I found was that a fair amount of the fluid had evaporated. Didn't hurt the film. Didn't hurt the drum.
I try not to make a habit out of it. But I don't worry too much about it either. But of course, using different chems, different drums, different films, etc. means that YMMV.