1958 Rare Glass Filled Pottery Dish by "Harding Black"

I have an unusual or rare piece of pretty art glass/ pottery that is signed Harding Black. Measures 6 1/4" across.
The inside of the dish is filled with a beautiful deep layer of green and blue melted glass cullet. I don't see this in his posted works.
This is a very well know American potters work.

Harding Black San Antonio (1912 - 2004)
Harding Black was born on a farm in Nueces County between Ingleside and Aransas Pass and moved with his family to San Antonio in 1916. There he graduated from Brackenridge High School and attended San Antonio Junior College (1929-30). In 1931 Black joined an archaeological expedition to the Big Bend area sponsored by the Witte Memorial Museum. Initially a painter, he was taught by Rudolph Staffel in 1933 to make wheel- thrown pottery and in the same year began to teach children's ceramic classes at the Witte.

Between 1937 and 1939, Black directed ceramic installation in a San Antonio reconstruction project sponsored by the National Youth Administration and the Works Progress Administration art program. In 1955 he retired from teaching and devoted his time to ceramics. Black became a well-known ceramist from his research, innovations, and writings in the field.