There is apparently an article on the Hummel Bonnet in the Nov/Dec 2003 edition of Piecework. Might have to get my hands on that...
other research notes from the web:
That picture can't possibly be the right gauge!!!
The hats to be laced either with gold or silver, as hearafter specified, and to be cocked uniformly. [The Black Watch, on the whole, wore highland bonnets, descriptions of which appear below]
The highland bonnet was one of the least standard items of the Black Watch soldier's uniform. Most bonnets were simple dark blue wool, with a red ball and band around the edge, though as the bonnet evolved, diced bands replaced the red ones and the bonnet grew taller, rather than lying on the wearer's head, cocked up on the left. The diced tall bonnets were more popular with the officers, suggesting that this practice was due more to fashion conisderations than anything else. The 42nd still wore a good portion of the flat older style bonnets through the American Revolutiuon, though by this time there was a combination of the two in use. The men wore tufts of black bearskin in the bonnets, and the officers wore a black ostrich feather.
You may sew a liner inside the hatband, but do not use dicing (checkered band) on the outside of the hatband. Dicing is of a later period. While "touries" or "pom-poms" are acceptable if they are small and unobtrusive, they are not necessary and are seldom seen in portraits of the period.
*note to Self* Can't see any difference between a tam and the requested hat, except for the dicing, which seems to be a later period. What exactly is the time-frame that he's going for?