Archaeology Magazine - March 1961 - 22

Weathered

Glass

continued

tion apparently proceeds during the winter, when water
soaks into the soil, and ceases during the warm dry summer months, when less water, or perhaps no water at all, is
available. During the summer the layer of decomposition
products formed by the preceding active period becomes
dehydrated. The layer is compacted and becomes physically separated and distinct from the remaining glass. In
the following active period water seeps through the porous layer and the cycle is repeated. On the basis of
chemical evidence it is not to be expected that the layers
accumulated through the years would coalesce into a
continuous mass, but rather that each would retain its
own individual identity.
Although glasses of different composition will corrode
to greater or lesser extents (and some are so stable that
no corrosion occurs), only the thickness of individual
layers varies, and the number of individual layers still depends upon the number of moist-dry cycles experienced.
In the case of objects continually submerged under
water, or buried underground in localities where there is
abundant and relatively uniform rainfall throughout the
year, prolonged changes in temperature, such as the
change from an average summer temperature to an average winter temperature, seem sufficientto cause layering.
The most important requirement for successful application óf the new method of dating is that the weathering crust be maintained intact. The factor most responsible for the present scarcity of suitable samples is the
tendency to clean excavated objects or remove weathering
crusts in order to get a better look at the object underneath. Often dealers and collectors intentionally flake off

Highlights

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Summer issue of

parts of the crusts to bring out the iridescence. Of course,
such pieces can no longer be dated by this method. In
addition, there are other limitations. Some glasses are
quite resistant to corrosion, while others produce crusts
which are so fragile that they cannot be handled without
causing serious damage. Over the years the abrasive action of soil will remove part of the crusts from these
more fragile objects.
The presence of a yearly cyclicalfactor in the weathering environment must also be justified. It seems that
such factors are more likely to be present in one form or
another than to be absent. It is also necessary to assume
that the weathering process started at the time of burial,
and this assumption also appears to be generally borne out.
In summary, it seems reasonable to say that this new
method is capable of dating accurately samples of weathered glass similar to the Colonial glasses already studied,
and that while further work is necessaryon fragments of
ancient origin, the results to date are very encouraging.
Archaeologists having objects which they feel might
be suitable for dating by this method are invited to submit small fragments for study. It is hoped that in their
future excavations they will be especially watchful for
fragments which they may wish to have dated.
THE AUTHOR,who has been Administratorof the Scientific
ResearchProgramof The CorningMuseumof GlasssinceFebruary, I960, studied at RutgersUniversity(Ph.D. 1954) and
thereaftertaught at Upsala College,New Jersey.The work of
developingthe new techniquedescribedhere was done in cooperationwith Mr. HarrisonP. Hood,Managerof the Chemistry ResearchDepartmentof CorningGlassWorks.Dr. Brill and
Mr. Hood have recentlypublisheda joint article on the technique in Nature (189 [1961]12). We are privilegedto'present
the first comprehensive
accountto appear in the United States.

AVDAT,A CARAVANHALT IN THE NEGEV
by AbrahamNegev
PREHISTORICMAN IN HAWAII
h wmiam 7. Bonk
STUDYINGTHE DIET OF ANCIENTMAN

FYRKAT,A VIKING CAMPIN DENMARK
by Olaf Olsen

Archaeology Magazine - March 1961

Table of Contents for the Digital Edition of Archaeology Magazine - March 1961