Bruce Robertson in his ‘WW1 British Aeroplane Colours and Markings’ Windsock Fabric Special No.2., has on page 7 that:

“The formula for producing 100 gallons of PC10 in this way was:
Nitro-cellulose syrup 260 pounds.
Pigments (see below) 74 pounds.
Castor oil 50 pounds.

The pigments for the 74lb above, were in the following proportions by ounces: Yellow ochre – 640, Umber – 480, Red ochre – 40, Chinese blue – 24.

These pigments were ground with the castor oil to which was added:
Acetone or methyl ethyl ketone 20 gallons
Amy acetate or butyl 15 gallons
Benzol 15 gallons
Methylated spirit 15 gallons”

I hope that is of use.