Long story, but my elders told me that DullCoat was simply clear lacquer with talc added to get the extremely flat finish it is known for.  This talc has two side effects, 1) it lightens the finish already applied to the model, and 2) it has some "tooth" to it allowing chalks, etc. to adhere to it.  Don't know if this is true, but that's what I was told.

-- John