Dear Bob,
	I use the term plate glass for the automated, thick poured glass
that started to be produced in the late 19th C.  Yes, Dederot shows
plate glass manufacture in France in the 18th c.  But that plate glass
was almost solely for mirrors.  I use the term window glass is used for
the thinner domestically used glass regardless of its manufacture.  
	The bluish or aqua glass is not soda glass.  Soda glass is clear
and typically develops a white patina after being buried or submerged.
The aqua color comes from iron in the sand which is used to make the
glass.  The more iron the greener the glass.  
	Regarding glass thickness and dates, Grant Day (2001)claims to
have used it successfully in dating a different parts of a 19th C. site
using the regression formula of Moir (1977). "84.22x (Glass thickness in
mm)+ 1712.7".  I have problems with this as I have measured a number of
large window glass fragments from a nineteenth century site only to find
that the thickness varied noticeably across each fragment.  Also, I have
not seen background research to indicate how standardized window glass
thickness is at a given time period.  Even today, you can get different
thicknesses of window glass at hardware store.  Guess what, the thinner
glass is cheaper.  There is a good chance that if a window pane is
broken, it may not get replaced with the same thickness of glass. This
is one reason that some windows rattle.       
	I do not know of any publications that indicate when clear flat
glass was first produced.  Remember, clear glass in the 18th C. was hard
to achieve and therefore more expensive and limited in use.  Clear flat
glass could also be from furniture and mirrors.  Today both clear and
aqua window glass is available.  There are photographs of English 17th
century windows with five or six different shades of almost clear to
aqua to green window panes.  (Noel-Hume 2005) 
	If the window glass fragments are large enough you might be able
to find the distinctive marks indicative of crown glass or tube glass.
Unfortunately, both processes were in use during you site's occupation.
	I believe that distribution analysis is still the best and most
reliable analysis that can be performed on window glass 

	I don't mean to be snarky, but doesn't any teach this basic
artifact information any more? 
	
Day, Grant
2001  Window Glass Dating: When was McConnell's Homestead Built? Paper
presented at the 4th Annual South Central Historical Archaeological
Conference, Little Rock, AK

Moir, Randall
1977  Window Glass: A Stistical Perspective.  Manuscript on file,
Archaeology Research Program, Southern Methodist University, Dallas, TX.


Noel-Hume, Ivor
2005 A Window on Williamsburg. "Something from the Cellar". Colonial
Williamsburg Foundation.
 
-----Original Message-----
From: HISTORICAL ARCHAEOLOGY [mailto:[log in to unmask]] On Behalf Of
Benjamin Carter
Sent: Friday, February 19, 2010 9:09 AM
To: [log in to unmask]
Subject: Plate Glass references

All,

I am having a bit of trouble finding references for the dating of plate 
glass.

There are, of course, far too many resources for bottle and table glass,

but I haven't had much luck finding out any details about plate glass.

I have mostly plate glass with a bluish cast, which I assume is soda 
glass. But, I also have, from the same contexts, some extremely clear 
plate glass. Why are these different? I assume that 'decolorizing' 
agents were use for the clear glass. Is there a time when this began. 
The site is fairly well dated- 1790s-1811. Would a change in glass types

have happened at this time? Or, is it likely that the clear glass is 
intrusive. Many of my contexts are fairly close to the surface.

Cheers,
Ben Carter