Just my two cp's with what I do...
Generally, I will try to dust wipe anything I bag. I have watched comic cleaning videos on YouTube where they are an excellent source of what to use and not use. I have practiced on some doubles to see what can be achieved with mixed results. Cheetos stains are not coming out no matter what you do.
Unless it is something extremely easy, like pencil marks, I leave it alone.
With
SW items, I take a very lightly moistened (if you can squeeze water out of it, it is too wet) soft towel and just wipe it down, avoiding any air holes or rips. Amazing what comes off with a little care. I then let it air dry for a day or two before bagging.
With hard backs, I will wipe them down to get rid of dust and crap that has accumulated on it while sitting on a bookshelf before bagging it.
I think the old stuff was done right, where TSR's early books were high quality and durable. I don't consider the Unearthed Arcana early, but what the heck happened to that book?
-SKA
