I’m painting Blue Moon. BR says he took the liberty to cover black canvas with Prussian Blue. I did that. BUT my white paint is turning into “ mud”. How long after applying Prussian Blue can I paint over it?
How long before painting on top of Prussian Blue
So I watched the first mins and I think I know what you issue is. When BR painted this videos, the paints were different in someways than what we have today. He constantly refers to a "Dry firm paint" for the Prussian blue. That is not what we have today in the BR paints. They tend to be oily and semi soft. Not as creamy as say Rembrant, but not dry and firm. To fake this, you can go a couple of ways.. one is to put a supply of PB on some cardboard for some hours and let the cardboard absorb some of the excess oil. Thats a old school trick to "dry" out a paint. Alternatively, you can use a drying medium to speed up the drying time of the paint but that requires more skill between how much medium to use and what does "dry" really mean. I use both myself but for this, I would use the cardboard. It's more forgiving and more in line to what BR is working with. If you already have mud, I would scape off what I could and then give a fast wash with a papertowl/OMS and start over. The canvas will be stained but thats ok 
5 days later
MACAL I always use liquid clear on the black canvases. I think that sometimes Bob forgets to mention that he has liquid clear on first.
6 days later
I have the same issue, usually with Alizarin Crimson. When I want to be sure the crimson stays true I use Winsor soft mixing white instead of titanium. It lightens and brings out the color without flattening it.