Clay Slurry Tank Cars

[Sumpter250]

I really wasn't paying much attention to tank cars until somewhere in the early 80's when I suffered a bout of "disieseization", when I started scratchbuilding / kit bashing some CNW diesels ( SD-60,SD-70, GP-15 ). Saw a lot of Kaolin cars in the Waukegan yard, but that was...early-mid 80's. As I understand it, Kaolin, was originally processed and shipped in boxcars, as a clay. It wasn't until the Kaolin clay got mixed with water and made into Kaolin Slurry, that tank cars were used to transport it.
I found one reference to Kaolin slurry, and ships: A business for transportation of Kaolin slurry in ships was founded in 1978.
This was the earliest mention of the subject I could find on my s l o w computer so there may be earlier references to shipping the product, but I have a feeling that it won't be much earlier.
You might try searching "patents" for the manufacturing process / shipping process.