The latest discussion I could find on this was three years old so I decided rather than replying to it I would start a new topic.
The last couple of days I've been doing a major decaling project with decals maybe six years old that are rather thick. I first tried using the Strong Version of Daco Products Decal Setting Solution and it didn't perform well. I tried Micro Sol but it was no better.
In the threads I could find on this topic the question of is solvent white vinegar or not came up several times. Now when I smell solvent I don't smell vinegar at all. I DO smell vinegar when I open an old jar of Testors Decal Set, which is used to clean and wet the model surface in preparation for the decal. When I smell both Micro Sol and the Daco product I get a mild Acetone smell.
So I found some old decals and a painted piece of plastic with both bumps and grooves, put a layer of Pledge on it, let it dry, and then affixed two old decals to the plastic. One I treated with pure white vinegar and the other I treated with my wifes finger nail polish remover (composed mainly of Acetone).
The vinegar treated decal did NOTHING! The Acetone treated decal immediately wrinkled up and started to suck down around the bumps and into the grooves. Now after fifteen minutes the wrinkles are gone, it has sucked completely down, and it looks great.
Now I don't know if finger nail polish remover will work on all decals and it may be too hot for some decals straight out of the bottle, but I'm going to try it on my next decal for the project I'm working on and we'll see what happens IRL.
Steve