From: The Discipline of the Light Horse by Capt. Hinde, 1778 (pg 559) -
"A Receipt for the White Belts. Take 1 ½ lb of Pipe-clay, 3 Quarts of Water, ¼
lb of Best Glue, ¼ 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 a with a Sponge in the usual manner, and when
Dry Rub it with a Glass-Bottle."
Vielen Dank an Alex Bosch von den Briten, von ihm ist die Quelle.