Warren in Lancaster, PA
The 11/16 measurement is on page 57. I think that mid 18th century mortise chisels are lighter yet. My experience is that for deep mortises a thick chisel is more work, because it clogs up the exit. A 1 inch deep mortise might make a nice demo, but most 18th century mortises are considerably deeper. Bill Tindall's mortises ought to be a lot deeper than one inch.