Knox porcelain signals
 Start up date was 1923 in Knoxville, Tn. and production ended
in 1975.

  Reported styles: U-285A, U-301, U-316, U-318

  Reported colors: choc. brown, white, brown, lt. blue, cobalt,     
green, olive green
U-301 recess embossed on skirt.
U-318s all recess embossed on skirt.
Brown U-318 radio treated Knox.
Newer ink stamped, marked "KNOX/1974 W".
Similar to a U-285A. Has a radio treated pinhole.
PP/KNOX combo is ink stamped. Similar
to U-285A. Has a radio treated pinhole.