Radiocarbon Age of Archaeological Consolidants and AdhesivesUsed in Archaeological ConservationCarley Crann, A.E. Lalonde AMS Laboratory (uOttawa)Tara Grant, Canadian Conservation Institution (Ottawa)

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Mea

sure

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Actual sample age (BP)

5% fossil carbon

no contamination

modern contam

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Consolidants and adhesives used to conserve archaeological artifacts must be carefully removed prior to radiocarbon dating of the artifact. It is therefore paramount to understand how the artifact was conserved and which conservation products were used in order to determine:

(1) the best location on the artifact to sample (2) how to remove the consolidant physically and/or chemically (3) whether or not the consolidant was successfully removed

The first two considerations are a matter of communication between the archaeologist, the conser-vator, and the radiocarbon laboratory, but the third consideration can be a bit tricky to determine.

The archaeologist usually knows the approximate time period of the artifact given the context in which it was found so when the age is not as expected, it is possible the consolidant was not com-pletely removed. However, without knowing the radiocarbon age of the consolidant – this is purely speculation.

Here we present results from the radiocarbon analysis of 20 consolidants and adhesives com-monly used for archaeological conservation. The consolidants and adhesives cover both natural (animal and fish glues, tree resins, starches) and synthetic materials (acrylics, poly (vinyl acetates), poly (vinyl butyrals), polyethylene glycol, glycerol, cellulose ethers, cellulose esters, cyanoacrylates and soluble nylon) and are selected from those commonly in use now, as well as a few that were used historically but are now avoided due to poor aging qualities.

Little is known about what effects conservation treatments used to bond or consolidate archaeo-logical material have on radiocarbon dating. This paper will present data that may indicate in which direction – young or old – conservation treatments may skew radiocarbon dates, the importance of knowing the history of older samples and how these results should be interpreted.

Effect of contamination on a radiocarbon date

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Increasing F14C14C “dead”Increasing potential for contamination

Equivalent radiocarbon “age” in yr BP

Colophony resinRabbit skin glue

Technical gelatineWheat starch Aytex-P

Sturgeon glueH.M.G. cellulose nitrate

Klucel GPaleoBond PB40

Rhoplex B60A (Primal B60A)Glycerin

Rhoplex AC-33 (Primal AC-33)

Bulldog gripAYAF

Paraloid B-72Butvar B-98

Carboway PEG400Soluble nylon (Calatron)

PVA Jade 403AYAACarboway PEG 3350

Acrysol WS-24

Group 1. Modern 14C signatureBiologically sourced (plant and animal)

Group 2. Mixed agesModified biogenic products

Group 3. 14C “dead”Petrogenic sourcesSynthetic polymers, acrylic compounds

Case Study: Charleston Lake Vessels - dated before and after consolidant removal

4

7

5

Impregnated under vacuum in 20% solution of PVAC AYAA inethyl acetate and toluene.

First attempt successful.

OxCal v4.2.4 Bronk Ram

sey (2013); r:5 IntCal13 atmospheric curve (Reim

er et al., 2013)

9000 2000300040005000600070008000 1000Calibrated Date (BP)

R_Date UOC-1643

R_Date UOC-1951

Vessel 4

Median = 3002 cal BP (1052 cal BC)

Median = 2345 cal BP (395 cal BC)

R_Date UOC-1644

R_Date UOC-1952

Vessel 5

Median = 7530 cal BP (5580 cal BC) Median = 2589 cal BP

(639 cal BC)

R_Date UOC-1645

R_Date UOC-1953

Vessel 7

Median = 1419 cal BP (531 cal AD)

Median = 1643 cal BP (307 cal AD)

Contaminated by consolidant Consolidant removed by solvent wash:hexanes (45oC, 1hr) acetone (45oC, minimum 1hr) 2 x 1:1 methanol:chloroform (25oC, 1hr each)

Impregnated under vacuum in 20% solution of PVAC AYAA in toluene, ethyl acetateand ethanol. The consolidation process was not successful.

The second time it was vacuum impregnated in a 20% solution of PVAC AYAA intoluene, ethanol, and Canadian Lacquer thinner. The second impregnation processwas more successful, however, iron deposits seemed to affect the final finish.

Impregnated under vacuum in 20% solution of PVAC AYAA in toluene and ethyl acetate.The consolidation process was not successful.

The second time it was vacuum impregnated in a 10% solution of PVAC AYAA intoluene, ethanol, and Canadian Tire Lacquer thinner. The second impregnation processwas more successful, however, iron deposits seemed to affect the final finish.

Three Charleston Lake samples were selected to test assumptions concerning temporal trends in Middle Woodland decorative motifs - pseudo scal-lop shell impressed (last half of the �rst millennium BC) and cord wrapped stick impressed (�rst millennium AD). The dates con�rm these expecta-tions, and re�ne trends in vessel form. Particularly interesting is the revised Vessel 5 date, as it sits squarely within the revised temporal range for Vi-nette I ceramics (Tache and Hart 2013). It is not unique in its antiquity with regard to other "Point Peninsula" dates from southeastern Ontario, such as the Wyght site (Spence et al. 1990); however, it is situated in the problematic Halstatt plateau, thus the precision is low on the calibrated date.

Acknowledgements. We would like to thank Shari Prowse (Ontario Ministry of Tourism, Culture, and Sport, London), Bill Fox (Trent University), and Jean-Luc Pilon (Canadian Museum of History) for providing the organic residues from Charleston Lake for a case study. We would also like to thank Alenandre Hardy-Mercure for assisting with sample preparation.