An Improved Pretreatment Protocol for Radiocarbon Dating Black Pigments in San Rock Art

Abstract

ABSTRACT. The dating of South African rock art using radiocarbon is a considerable challenge and only 1 direct date has so far been obtained, on black pigments from Sonia's Cave Upper, Boontjieskloof. The main problem with direct dating these paintings is the presence of calcium oxalates behind, on, and within the pigment layers. Calcium oxalates are formed through lichen and bacterial action on the rock face. These reactions can sometimes take place over long periods and can incorporate carbon of a younger age into the pigments. This study aims to date black pigments from a rockshelter, RSA TYN2 (Eastern Cape, South Africa), by removing the calcium oxalate contamination. Two different protocols were tried: density separation and acidification. The latter successfully removed calcium oxalates and was therefore applied to 3 black pigment samples from the rockshelter. After acid pretreatment, accelerator mass spectrometry (AMS) dating was undertaken on the remaining residues. Three results were obtained (2072 ± 28 BP, 2100 ± 40 BP, and 2083 ± 32 BP), which constitute the oldest results so far obtained for direct dates on South African rock art. The most likely calibrated date range for the painting at this site is between 2120 and 1890 cal BP. The ages are in close agreement with each other and this consistency suggests that our preparation protocol has successfully removed the majority of the carbon contaminants.

A multi-technique characterization and provenance study of the pigments used in San rock art, South Africa

“…Three results were obtained (2072 AE 28 BP, 2100 AE 40 BP and 2083 AE 32 BP), which constitute the oldest results so far obtained for direct dates on South African rock art. The most likely calibrated date range from these three results at RSA TYN2 is between 2120 and 1890 cal BP (Bonneau et al, 2011).…”

Rock Art and Sacred Landscapes

“…Neither do we know how old the paintings are (cf. Bonneau et al 2011Bonneau et al , 2012; they may or may not predate the arrival of agro-pastoralist groups. This lack of chronological certainty, however, is not indispensable to the argument developed here; more important is the fact that it is unlikely that the ritualistic images illustrate a literal or a narrative event.…”

Successfully Dating Rock Art in Southern Africa Using Improved Sampling Methods and New Characterization and Pretreatment Protocols

“…On the other hand, calcium oxalates have received very little attention as they are rarely identified in common radiocarbon samples. During the initial project at the ORAU (Oxford Radiocarbon Accelerator Unit), preliminary tests were conducted on calcium oxalates and published by Bonneau et al (2011). Tests conducted for the present project aimed at reducing the time that samples need to be immersed in acids and bases whilst efficiently removing the radiocarbon contaminants.…”

“…Following the initial tests conducted (Bonneau et al 2011), a modified ABA (Acid-Base-Acid) pretreatment was established. However, to try to reduce the quantity of sample to be taken, tests were further undertaken to adjust the length of each step to avoid as much as possible the loss of sample.…”

“…To assess this problem, the first characterization and pretreatment protocol (Bonneau et al 2011) has been extended and improved. It aims to select the paints that would be the most likely to be successfully radiocarbon dated by using a multi-instrument protocol.…”