Clay Electric Oven?

I was speaking with an older friend today, and she mentioned that in 1961 she lived in Maryland in a community called Greenbelt and the kitchen ovens there were made of clay.  In the base there were grooves in the clay for coils.  She said it was great for baking.   No kidding.   Does anyone know about these ovens?   Do they still exist?  Thanks.  -Varda