Several decades ago when bentonite was introduced to the steel foundries of America as substitute for fire clay in sand bonding. It won rapid approval due to its more desirable combination of green & dry properties. Bentonite-bonded sands molded better and peeled from the castings better, and shakeut was improved, with less lumping of the sand.
The bentonites came from South Dakote & Wyoming in the Western part of the U.S.A., and when similar deposits were discovered in the South, the types were identified by the prefixes ‘Western’ & ‘Southern’. The southern bentonites, while having excellent properties for some types of molding, did not prove satisfactory in the steel foundry. For many years western proved so successful in the ‘Western’ and the suppliers consciously provided western bentonite.