Interesting topic- yes at some times  size varies probably more earlier 
than later however across a large enough site
with enough window openings there should be some correlation in general 
terms. The interesting thing is that appearance of
window glass types will be cummulative with earlier panes lasting 
through time being broken and not totally replaced with new.
Therefore the more variation in thickness the later the context. Then 
again one must be careful that one is not looking at small pieces of
very flat bottle glass panels or indeed mirrors or other applications- 
such as windows for cash registers....enclosed book shelves, picture 
glass....context is everything.

Conrad Bladey

Doms, Keith wrote:

>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
>
>  
>