Crossing the Borders: New Methods and Techniques in the Study of Archaeological Materials from the Caribbean

Dental Alginate Molds of Friable Artifacts / 71
Methods and Materials
Dental alginate is readily available in many proprietary brands. Jeltrate® Plus Fast
Set (Dentsply International, Milford, Delaware) was selected for this study. It is
light and transports easily as a powder, has low dusting character, and requires no
special apparatus. Table 5.1 outlines the protocol.
Any cool, clean, freshwater source is acceptable for mixing the alginate and
dental stone. Saltwater adversely affects the alginate mix, preventing it from properly
setting up. Casts can be made of any plaster material, but because of durability
and fine detail retention, dental stone is preferred. Vel- Mix® dental stone
(Kerr Lab, Orange, California) was used for this project.
Durability of the Molds
A shrinkage study was conducted to document the durability and stability of the
alginate molds. Molds made in the field as well as fresh samples were used in the
study. The first measurements were taken in August 1995 with the final measurements
in December 2005. All of the molds were stored in individual zippered heavy
plastic freezer bags in a covered cardboard file box in ambient temperatures of 68°
to 75°F. At the time of the final measurements, all molds were firm to the touch, but
many remained partially flexible and, with care, these were still usable for casting.
New casts made from these partially dry molds do not provide accurate measurements.
Pattern detailing was still clearly visible for study purposes even in the totally
dry examples. All of the molds in bags that retained their integrity remained
semiflexible.
The final range of shrinkage dimensions was 0.7–14 mm; 11 to 31 percent. Table
5.2 gives the shrinkage rates over time. Circular and elongated objects had the
highest initial shrinkage rate, approximately 1 percent per week for the first three
weeks, while irregular shapes had the highest dimensional stability during that
time (Table 5.2). For the most part, this equalized by the end of the study, with
rectangular forms ultimately shrinking the least, averaging 5 mm or 15 percent
overall. After ten years, many of the molds stored in near optimal conditions remained
in good condition. Mold durability is adversely affected by exposure to direct
sunlight, heat, rough handling, compression, and exposure to air.
When evaluating the effects of the alginate compound on the study collection,
no detectable surface residue or damage has been noted over the past ten years.
However, at the time of molding, some crumbling was noted at the most friable
edges. Additionally, water- based pigments painted on sherd surfaces are in potential
jeopardy of removal by contact with the wet alginate (Drooker 2001). Slip decoration
fired onto the ceramics will not be harmed. The 1999 Society for American
Archaeology Working Group in Impressed Pottery concluded that since all of the
compounds used for taking molds and casts of impressed ceramics may leave some
form of residue, examples of each type should be set aside so that other analyses
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