My curiosity was piqued ... so I consulted ... "The Encyclopedia of Photography", Volume 3, pages 398 - 399 - copyrighted MCMLXII - MCMLXXVIII (1962 - 1978) - an entire article titled "Baryta Coating for Papers" by H. E. Smith of the Eastman Kodak Company.
In it he describes the "new" refined barium sulfate (BaSO4) known as "blanc fixe" - an improvement over the previous - cruder - forms of baryta used in the past.
Hmmm ... "It is also a by-product in manufacturing hydrogen peroxide from barium peroxide ... "