Interesting about the powdered charcoal vs. chalks with flat finishes.
I thin the Vallejo black with straight 70% alcohol.
The idea of using water with a bit of dish detergent never occurred to me! I will try that on the next car I weather. If it does allow the wash to properly wet the surface my issues with decals reacting to the alcohol will be over.
I seem to recall some folks using straight iso alcohol to strip off lettering and/or paint.
I use a little tupperware cup with a cover, it’s probably about equal to one measuring cup. Except for maybe a teaspoon of alcohol and that much or less of acrylic paint, the rest is just water.