Dear all,

Thank you all very much for your information, especially to David Moyer 
for the extensive bibliography.

You will all have to forgive me for my faux pas of calling my "window" 
glass by the incorrect term of plate glass (Doesn't the term "window" 
predetermine function? Are there other functions for "window" glass than 
for windows?). Irregardless, I will use window glass from now on.

I was aware of Moir's equation, etc... but it is inappropriate for these 
contexts as they are mostly surface, the sample size not large enough 
for statistical significance and this is a preliminary report. To spend 
all that time measuring shards of glass would not be well spent. I am 
happy to spend time in such an enterprise- I spent thousands of hours 
measuring nearly 10,000 shell beads and 1000 lithic drills for my 
dissertation. Such an expense would not be productive in this case.

I was hoping that there was some big change in glass technology that 
occurred where "window" glass went from having a colored cast (aqua, 
etc.) to being very clear. I assume that transition happened when 
decolorizing agents were used. Bill Lindsey (on the bottle 
identification website within the SHA website) indicates that 
decolorizing is quite old- 15th century, but he also appears to indicate 
that decolorizing bottles was not common until the late 19th century 
into the 20th century. That, of course, is in reference to bottles, what 
about window glass?

Was there a point in time when decolorized glass become much more prevalent?

Overall, I have to admit that this is not a large issue for the 
particular report that I am working on right now. If it was, I would 
have spent much more time working on it myself. I sent the message to 
Histarch in the hopes that there was a small, but important detail that 
I was missing. Alas, I have not heard much on that point, though there 
is likely something in Moyer's bibliography.

Thanks again for all the help and if anyone has more info on decolorized 
window glass or anything else, I'd love to hear more.

Cheers,
Ben (not Bob) Carter


On 2/19/2010 12:51 PM, 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
>
>