Core drills

In response to George Hagerty's query on core drills:

Core drills are not generally used to obtain sample for TL, as a
powder sample is needed. They are generally used to take a core
sample, producing (hopefully) a solid disc of ceramic, often used
for SEM or thin section petrographic analysis. The diamond abrasive
used on the core drill would contaminate a TL sample, producing it's
own signal.

For TL sampling, Oxford Authentication Ltd. asks for 100 milligrams
of sample, although that can make a relatively large/deep hole and
we often supply only 40-50 mg. Two smaller holes may be called for.
The size, nature, wall thickness of the vessel are among the
variables to be considered, as is the aesthetic impact. The powder
sample from the beginning of the hole  must be discarded to avoid
surface contamination and/or depletion of the constituents from
weathering/burial.The sample is taken in the darkroom, with a
safelight, and thereafter kept from light.

TL sampling is done here at the Straus center with tungsten carbide
twist drills. A 2.5 mm bit is a typical size, although larger and
smaller bits are used as conditions require. We order both types
from:

    Chandler & Farquhar Co.
    60 Shawmut Rd.
    Canton MA
    02021
    781-961-0011
    800-631-4700

They have a terrific catalog.

Tony Sigel
Harvard University Art Museums
32 Quincy Street
Cambridge, MA 02138
617-496-1903
Fax: 495-9936


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                  Conservation DistList Instance 13:41
                Distributed: Thursday, January 27, 2000
                       Message Id: cdl-13-41-001
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