vintage Frankoma pottery, large platters, Plainsman brown squared oval plates

Pair of vintage Frankoma pottery platters or oblong plates, about 13 1/2" long. These are both in very nice condition without damage, showing little if any wear.

These are the Plainsman brown glaze, I believe? The clay is visible at the foot on the bottom, but I'm not really familiar with the different ceramic clays, sorry!