In the U.S., Western Electric sold Chatterton's compound, and it was
available in domestic and imported versions in various grades.  The
domestic version was last made by Emerson Electric.  Production of
domestic product stopped about five years ago.  The imported version
was of higher quality and was considered waterproof.  The grade
(performance characteristics) was changed by varying the basic
proportions of the materials used to make the product.  Somewhere
around here I have the details on the formulation and on some of the
performance changes from differences in the mix.  Gutta-percha is a
form of latex.  Stockholm tar refers to a particularly high grade of
tar from pine trees.

Wm. G. Chapman
West Point, NY