Abstract
Discussions of heat treatment in the southern African Middle Stone Age often focus on the importance of this innovation to the development of complex technologies and the evolution of modern human cognition.
1. Introduction
Heat treatment, the intentional alteration of lithic raw materials to improve their quality for tool production, is viewed as an important technological innovation in human evolution.
2. Materials and methods
We analyzed nine samples from five sources ( Fig. 1 ). Three derive from the Cederberg mountain region of South Africa, two of which are in the Doring River catchment (sources AGF, SWV) (n = 4) and the third from the Olifants River catchment (RG, n = 2).
3. Results
Changes in H 2 O content for all samples are shown in Fig. 4. All samples show a decrease in H 2 O content from the lowest to highest temperatures, but differences in initial H 2 O concentration, the temperature at which changes begin, and magnitude of change are observable.
4. Discussion
Differences in starting concentrations and degree of change in H 2 O, SiOH, and pore volume were present across sources. Samples from sources MHS and ALF recorded the greatest changes in H 2 O and SiOH concentration while concentrations in samples from source RG changed the least.
5. Conclusions
The structural composition of silica rocks affects their heating tolerances and thermal-induced changes to mechanical properties. Results from Mackay et al. (2018) suggest a possible relationship between the structural changes that occur within silcretes and their rate of failure from overheating when heat-treated quickly to high temperatures.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Abstract
In archaeology, heat treatment is the process of intentionally modifying lithic raw materials to improve their knapping quality.
Introduction
Heat treatment of lithic raw material is the process of intentionally modifying a rock to improve its knapping quality. The technique was first practiced in southern Africa during the Middle Stone Age (Brown et al. 2009; Mourre et al. 2010; Porraz et al.
The measurement of reaction kinetics by in situ Raman spectroscopy
In accordance with the model of thermal transformations of silica rocks (Schmidt et al. 2012b, 2013b ), the time a rock must be held at the maximum heat treatment temperature can be expected to depend on the kinetics of reaction (1).
Samples and experimental protocol
We selected three samples of flint and chert of different geological age and provenance (Table 1) representing different structural and mineralogical features (see “ Results and discussion ”).
Results and discussion
The thin sections of all three samples reveal them to be mainly composed of length-fast chalcedony. Sample PS-09-04 also contains dispersed calcite remnants from before the silicification of the chalk host rock (about 4 % as semi-quantitatively determined by XRD).
Implications for lithic heat treatment
Combining our results with previously published data, we can try to estimate the investment in time needed for heat treatment of flint and fine chalcedony containing chert.
Conclusion
Our analyses of the thermal transformations’ reaction kinetics in flint and chert showed that these types of rock do not need to be held at maximum temperature for longer that 1 h. Even significantly shorter times at T max produce rather intense transformations.
What are the defects in steel due to heat treatment?
Principal defects in steel due to heat treatment and measures for their elimination: 1. Overheating: Coarse grained micro- structure and fracture.
What temperature should I use for overheating?
ii. For considerable overheating, use double annealing or normalising; first annealing or normalising at temperature of AC3 + 100°C to 150°C, second at normal temperature. 2.