There is probably about a dozen of different brands of decal setting solutions out there. Lets see:
Microscale MicroSol and MicroSet Gunze Sangyo Mr. Decal Softer Walthers Solvaset Champ Decal setting solution SMP Decal setting solution (probably out of production). Floquil Polly S Decal Setting Solution Testors Decal Setting Solution
And several others which I don't recall the specifics on. FSM Magazine even ran a full feature article on various decal setting solutions, techniques and compatibility. That was several years ago.
Basically, there are 2 types: Acid based and alcohol (solvent) based. And they all have different strengths.
I've used most of the ones I've mentioned over the years on various projects and various decal brands. But I don't keep detailed data on how I've used them (I should...)
I expect that you'll get many replies on this topic and everyone's opinions will be different. There are just so many different combinations of decal brands and setting solution brands. You'll have to be more specific on which brand of decal you have or you'll have to do some experimenting on your own.
Instructions provided on the bottles are actually pretty good.
Peteski