NIcrobraz stop offs, manufactured by Wall Colmonoy, come in three flavours – white, red and green.
From memory, White stop off is Titanium Oxide based, Red is Calcium Carbonate based – can't recall what is used in green stop off. I could be wrong – it was a long time ago.
Stop offs came as a paint-on liquid and also as wax sticks.
I used to be the technical sales rep for Colmonoy forty years ago; The UK factory (they are an American company with head office in Detroit) is just two miles from me in Pontardawe and they are going strong.
Martin.