Hi Jeremy,
Are you inquiring about manufacturing techniques for chronometric purposes?
I can give you other references and info on viewing window glass generally,
but actually there are a lot of potential problems that you can encounter when
attempting to apply flat glass dating techniques to viewing windows in burial
containers. My experience for this comes from a number of cemetery
excavations, most notably the Freedman's Cemetery Project.
As you know, the total Freedman's data set on this is huge. At the close of
excavations at Freedman's Cemetery in 1994 we had archeologically excavated
and analyzed 1,150 burials containing 1,157 individuals (on about an acre of the
4 acre cemetery). Of this number, 369 (or about 1 in 3) were associated with
coffins or caskets containing viewing windows.
Back in 1993, I sat down with Randy Moir in my office at Freedman's Cemetery,
and discussed this matter specifically. Randy was there to get my advise on
an isolated late 19th century burial he had just excavated on a contract job,
and we discussed the flat glass dating technique at length. I pointed out my
measurements thus far collected, and I told him that the formula just didn't
work. He agreed, and identified at least one reason why; that window glass in
commercial coffins and caskets are almost always double thick glass, not
single thickness, which is what windows in houses are made of.
Rather, it appears that the glass was more often than not specialty glass;
glass panes or lights could be commonly purchased in standard single thickness,
or in double thickness. For example, in the 1883 George N. Lee & Company
Catalogue (of Chicago, Illinois), panes of picture glass were sold in "single
thickness" or "double thickness" varieties (George N. Lee & Co 1883:88). Double
thick glass was often used in furniture manufacture, such as china and curio
cabinets, as well as coffins.
Double thick glass was available for purchase since the mid 19th century at
least, and probably earlier. All of the various formula and dating curves
(Moir's, Roenke's curve for the Pacific Northwest, et al.) don't take this
specialty glass into account. These formulae are made for single thickness, not
double thickness, and they cannot be integrated into the mix just as easily as
punching in the numbers.
There are additional problems with dating viewing window glass. A lot of the
glass in coffins was specifically described as "imported glass," often
referred to as "French glass." Although this might seem a bit odd, I stumbled
across this fact while mining information from my large collection of 19th century
coffin and casket catalogues, for the Ft. Smith Cemeteries report. For
example, in the early 1880s from more than one wholesale coffin manufacturer, the
customer had the choice of purchasing either "American or French Glass." Some
19th century coffin catalogues specifically state that all of the glass used in
their viewing windows is "French Glass" (e.g, Columbus Coffin Company
1882:4-8; Hamilton, Lemmon, Arnold & Company 1884:4; Warfield & Rohr circa 1890:3).
Because they used different manufacturing techniques, at different times,
this import glass likely does not mesh with any flat glass dating curve created
for American glass.
Some windows were even thicker than double thick glass. In metallic burial
containers with viewing windows, the glass panes are often extremely thick.
For example, Burial 312 at Freedman's Cemetery in Dallas (Davidson 1999), was
interred in a cast iron and sheet metal octagonal casket , with a glass
thickness that averaged 10.75 mm. The viewing window glass associated with the cast
iron coffin of Colonel William Crawford (who died in 1874 and buried in Benton,
Arkansas) was also very thick, at 5 mm (Davidson and Black n.d.). Both of
these would blow the top off of any flat glass curve. In period catalogues, the
viewing windows associated with metallic caskets are occasionally referred to
as "Heavy Plate Glass" (e.g., Harrisburg Burial Case Company circa 1890:13).
Here's a example of how dating viewing windows works out: At two rural
cemeteries near Fort Smith, Arkansas, dug by the Arkansas Archeological Survey, 5
burials had viewing windows. To see if viewing window glass could be used as
a chronometric tool, the Moir flat glass dating curve (for single thickness
glass panes) was applied to these data. This formula, generated during Moir's
work on the Richland Creek Project in North Texas (Moir 1987), is: I =
84.22(T) + 1712.7, where I is the initial construction date, and T is the mean
thickness of the flat glass sample. When this formula was applied to the burial
window glass, the results were very disappointing. Burials 3 and 17 at the Eddy
Cemetery, and Burial 1 at the Wright Cemetery all had window glass thickness
that well exceed the range for single pane glass manufactured between circa
1810 and 1915. These burials, two of which are tombstone dated to 1885 and 1896,
have windows that are obviously double pane glass. All three of these window
dates were decades off.
Of the remaining two interments -- one tombstone dated to 1893, another with
an estimated date of interment range of 1890-1900. The dates derived from
flat glass dating are 1898 and 1871, respectively. One close (albeit in the
wrong direction), and again, one decades off, this time, into the 1870s.
So, what can we do with flat glass dating in mortuary contexts? First, the
use of double thick glass panes (or thicker) and second, the mixture of both
domestic and imported glass within the casket industry, combine to prohibit the
casual application of any previously established dating curve or formula.
Perhaps in the near future, with a greater knowledge of glass sourcing in 19th
century burial containers, as well as a greater sample size of burials
(especially those with known dates of interment), it may be possible to use glass
thickness as a dating tool (in certain instances) for those unmarked graves
associated with viewing windows.
Hope this is somewhere in the ballpark of what you were asking.
Dr. James M. Davidson
Assistant Professor
Department of Anthropology
University of Florida
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