Ray,
 
The place to start is probably Don Ball's paper, "Approaches Toward the Dating
of 19th Century Ohio Valley Flat Glass," p. 129-137 in V. I (1983) of the
<Proceedings of the Symposium on Ohio Valley Urban and Historic Archaeology.>
 
There may well be more recent attempts at using the changing thickness of flat
glass to date Historic sites.  I know that Jeff Carskadden had some success
with this at a ca. 1820 iron furnace site in Muskingum Co., Ohio, reported in
the <Pennsylvania Archaeologist> but don't have the specific reference at hand.
 
As it happens, I think there is a paper being given on this topic at this
year's Ohio Valley conference, which is being held next week in Greenville,
Ohio.  I don't have a copy of the program but will be attending and can at
least put you in touch with the author(s) of that paper, if someone else on the
list is not able to do so before then.
 
If you do not have ready access to the Ball paper, let me know and I can send a
xerox.
 
You might want to contact Don Ball directly, 1 (502) 582-5696, about this.
 
Jim Murphy
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