Under smoked brain tans will turn hard if soaked and left to dry I think, {as will some alum tans or tawed leathers }...they used to write in the mountain man novels and books etc about this problem, and that old leather from the smoke flaps of a tipi was the best stuff to make moccisins and pants from to aviod the hardening and shrinking that would happen if the native brain tanned skins got soaked and dried...from exposure to the elements or trapping streams etc...Sounds reasonable?
T.C.Albert