The only thing you need to avoid soap ash is a spray bottle with a very strong alcohol solution. (96%)
1) Make your CP soap as usual and pour it.
2) Wait a while and when the soap starts to condense and the surface goes from being shiny to being more matte (this is the stage just before the soap reach a gel, the soap should be condensed enough to hold the marks of a spatula without smoothing out again), spray it evenly with the alcohol. Don’t use a spray which has a hard squirt like a water pistol. The alcohol should land lightly as a feather on top of the soap so it is distributed evenly. Don’t be afraid of using too much alcohol. The more ASH your soap has – the more alcohol you will need to dissolve it.
You need to repeat this procedure a couple of times more. Let the alcohol evaporate completely before you spray again. A strong alcohol on a warm soap will evaporate very quickly so you don’t have to wait very long. You know that you are finished when the soap has created a thin DRY, smooth and shiny film on the top. Push the surface of the soap with a finger; you can actually see and feel it.
I am no chemist but since I have made quite a lot of MP base lately, I think I have a good idea of what is happening. The strong alcohol works as a solvent and it dissolves the ASH layer while it is being created. What you get instead is a CP soap with a very thin top layer of shiny smooth non-transparent MP soap and believe me it really is shiny and beautiful.
If you do CPOP, you can spray them REALLY WELL before they go in the oven and then again about 1/2 hour later