Among the annoying traditions of some 18th-century British Army units (including the 7th Foot,) is buff leather belting dyed bright white for field use. Soldiering, even the pretend kind, is hazardous and unforgiving when it comes to fashion.
The Discipline of the Light Horse:
"Take 1 1/2 lb of Pipe-Clay, 3 Quarts of Water, 1/4 lb of Best Glue, 1/4 lb of White Soap, Boil the Soap and Glue first, till dissolved, then Mix it with the Pipe-Clay, and Boil all together for a Quarter of an Hour; when Cold put it on with a Sponge in the usual manner, and when Dry Rub it with a Glass-Bottle."
Much easier to keep painting leather belts and wool white than use something that doesn't show mud/blood/scuffs. Idle hands and all that.
Hide glue is weird. Fortunately, it is still popular with the wood working set. The dry stuff soaks up a bunch of water over several hours and turns into a gelatinous puck. Be prepared to sacrifice one or two (cheap) pots to the gods. And how 'bout that smell?
Slowly add the hot water and clay to the soap and glue mess. At this point, it's best to take apart the double boiler and heat the mixture directly. Be prepared to scrape the bottom as you stir to prevent sticking.
White kaolin clay can be had here. Hide glue is here and many woodworking sites. Etsy is a good source for soap. A cheese grater makes short work of the soap cake.
Next, we defarb a tired knapsack.