Fellas,
I found this discription of sinew bowstrings that were "impermeable to snow and rain". These in the report were made by the Tse'kehne and Carrier tribes of Native Americans.
Both of the tribes made plain and sinew-backed bows but this method was used by both for their strings.
The following quoted from Otis Mason's 1893 report to the Smithsonian, and he is quoting Father A.G.Morice, Trans. Canad. Inst. , Toronto, 1894, IV, 58,59.
"Great care was taken to obtain a bow-string impermeable to snow and rain. With this object in view, delicate threads of sinew were twisted together and afterwards rubbed over with sturgeon glue. This first string was then gradually strengthened by additional sinew threads twisted around the first and main cord, each overlaying of sinew being thoroughly saturated with glue. Finally when the string had attained sufficient thickness for efficient service it was repeatedly rubbed over with gum of the black pine (Abies balsamea)"
a further quote of both reports describes the glue used as:
".....These pieces of sinew were fastened on with a glue obtained from the sturgeon sound, which also did service for all kinds of gluing purposes amoung each of the three tribes, while still in their prehistoric period."
This Sturgeon glue was obtained by boiling down the lower jaw and swim bladder of the sturgeon and was described as rather clear in appearance.