The Burke No.1 line was originally insulated with these M-3725 Fred M. Locke flappitybacks. The 6-1 marking dates production between January and July 1902. The top shell is really a mess on this side. All misaligned and lumpy. About as smooth as a glazed apple fritter. Note the odd light color spot up high on the middle shell. It appears some impurity was lodged near the surface of the shell, and during firing turned to glass, running out of the shell and down as a drip. See close up of green glass drip. [id=179337693]