[Accumulator climbs onto his carwash-topic soapbox...]
Here's how I test my wash media:
Needed- wash medium to be tested, bucket of shampoo solution, unmarred CD.
Test procedure:
-Dunk medium in shampoo solution, make sure things get not only saturated but also softened up (this can take a little while, something to consider when you wash too)
-Use shampoo-sodden medium to "wash" the data side of the CD, using the same amount of pressure you'd use when washing the vehicle
-Inspect CD for marring, using good lighting and magnification if needed
Once you ascertain that all your wash media are safe in-and-of themselves, you can start worrying about how to use them to move potentially abrasive dirt across-and-off the paint without marring it. That's the tricky part.
Here's a very short version of how I wash when using only mitts and a foamgun (i.e., in the absence of a BHB):
I don't consider the primary function of the foamgun to be the prerinse, in fact I hardly do that at all (just a cursory spray to "prewet" the surface). The big benefit IMO is the way the foamgun can provide constant flushing and lubrication of the surface being washed; it's a "dislodge and flush" approach. Here's my take on it:
The idea is to spray the foamgun output at the point where the wash medium contacts the paint.
Fill the mitt with shampoo solution and hold it shut at the cuff. Gently move the mitt short, interrupted, "jiggling" motions while spraying the foamgun output at the point of contact. Rinse out the mitt frequently, at the very least do it as soon as the shampoo you've filled it with stops seeping out.
Always inspect the mitt for residual dirt that didn't rinse out before refilling it with wash solution and resuming work.
Don't be surprised if the above approach is so gentle that you have to wash some areas more than once.