Differential etching after lithic heat treatment: First results of an experimental study

  • Linda Kiers
Keywords: heat treatment, double patina, white patina, artificial patination, differential weathering, SEM-sampling


The practice of lithic heat treatment creates a combination of initial dull flake scars and subsequent smooth flake scars when the implement is finished after heating. Experiments were done to test the susceptibility of dull and smooth flake scars to etching. The points were etched in 40% hydrofluoric acid for either 40 or 60 seconds. In the 40 seconds experiment, the smooth flake scars of 9 (out of 25) heated points showed less etching than the dull flake scars or no etching at all. These artefacts formed a weathering pattern that is similar to double patina in reworked flints. Ten unheated control samples did not form differential weathering between different generations of flake scars. In the 60 seconds experiment 4 (out of 25) heated points showed some parts of the smooth surface to be less affected. Ten unheated control samples did not form differential weathering. The experiments show that sometimes smooth flake scars are more resistant to etching initially.

In Scanning Electron Microscopy, flint artefacts are sometimes pre-treated with hydrofluoric acid. Heat treated flints are susceptible to differential weathering by hydrofluoric acid. Thus, pre-treatment with hydrofluoric acid of heat treated SEM samples can lead to surfaces that are etched to a different extent.

The chemical etching in this study does not replicate any natural patination process. How heat treated lithics respond to natural weathering processes cannot be predicted. Further studies should produce natural patination and test selected artefacts in contexts of intentional heat treatment for signs of heating.

Author Biography

Linda Kiers

I have completed the Research Master Archaeology (cum laude) at the University of Groningen (Groningen Instute of Archaeology). I have published two papers and a co-authored book chapter in the field of lithics. I am currently looking for a PhD scholarship.


Ahler, S.A., 1983, Heat treatment of Knife River Flint. Lithic Technology, 12(1): 1-8. URL: http://www.jstor.org/stable/41999761
Aubry, T., M. Almeida, M.J. Neves & B. Walter, 2003, Solutrean laurel leaf point production and raw material procurement during the Last Glacial Maximum in Southern Europe: Two examples from Central France and Portugal. In: Multiple approaches to the study of bifacial technologies (Soressi, M., & Dibble, H.L., Eds.), University Museum Monograph Vol. 115. University of Pennsylvania Museum, Philadelphia: p. 165-182.
Bäsemann, R., 1987, Umweltabhängige Strukturveränderung an Steinartefakten. Arbeiten zur Urgeschichte des Menschen Vol. 10. Lang, Frankfurt am Main, 111 p. (in German) (“Environmentally dependant structural change of lithic artefacts”)
Borradaile, G.J., S.A. Kissin, J.D. Stewart, W.A. Ross & T. Werner, 1993, Magnetic and optical methods for detecting the heat treatment of chert. Journal of Archaeological Science, 20(1): 57-66. doi:10.1006/jasc.1993.1004
Brown, K.S., C.W. Marean, A.I.R. Herries, Z. Jacobs, C. Tribolo, D. Braun, D.L. Roberts, M.C. Meyer & J. Bernatchez, 2009, Fire as an engineering tool of early modern humans. Science, 325(5942): 859-862. doi:10.1126/science.1175028
Collins, M.B., 1973, Observations on the thermal treatment of chert in the Solutrean of Laugerie Haute, France. Proceedings of the Prehistoric Society, 39: 461-466. doi:10.1017/S0079497X00011774
Delagnes, M., P. Schmidt, K. Douze, S. Wurz, L. Bellot-Gurlet, N.J. Conard, K.G. Nickel, K.L van Niekerk & C.S. Henshilwood, 2016. Early evidence for the extensive heat treatment of silcrete in the Howiesons Poort at Klipdrift Shelter (layer PBD, 65 ka, South Africa. PLoS ONE, 11(10): p. 27. Accessed: 28-10-2018. doi:10.1371/journal.pone.0163874
Domański, M., & J. Webb, 2007, A review of heat treatment research. Lithic Technology, 32: 153-194. doi:10.1080/01977261.2007.11721052
Domański, M., J. Webb, R. Glaisher, J. Gurba, J. Libera & A. Zakościelna, 2009, Heat treatment of Polish flints. Journal of Archaeological Science, 36(7): 1400-1408. doi:10.1016/j.jas.2009.02.002
Eriksen, B.V., 1997, Implications of thermal pre-treatment of chert in the German Mesolithic. In: Man and flint. Proceedings of the VIIth International Flint Symposium Warszawa - Ostrowiec Świętokrzyski September 1995, (Schild, R., & Sulgostowska, Z., Eds.) Polish Academy of Sciences, Warsaw: p. 325-329.
Flenniken, J.J. & J.P. White, 1983, Heat treatment of siliceous rocks and its implications for Australian prehistory. Australian Aboriginal Studies, 1: 43-48.
Frank, D.A., 2004. Heat treatment of lithic artifacts in early sites from the central Plateau of Santa Cruz (Argentina). In: Southbound. Late Pleistocene peopling of Latin America, (L. Miotti, M. Salemme, N. Flegenheimer & T. Goebel, Eds.), Peopling of the Americas publications, Center for the study of the first Americans, Texas A&M University, Bryan: p 4.
Franken, S. & S. Veil, 1983, Die Steinartefakte von Gönnersdorf, Der Magdalénien-Fundplatz Gönnersdorf 7. Franz Steiner Verlag, Wiesbaden, 437 p. (in German) (“The lithic Artefacts of Gönnersdorf”)
Gawel, R.P. & J. Weiner, 2010, Einzigartig im Rheinland! Eine Pfeilspitze aus getempertem Feuerstein. Archäologie im Rheinland 2009: 50-52. (in German) (“Unique in Rhineland! An Arrowhead of heat treated Flint”)
Goodwin, A.J.H., 1960, Chemical alteration (patination) of Stone. The South African Archaeological bulletin, 15(59): 67-76. doi:10.2307/3886559
Griffiths, D.R., N.J. Seeley & M.C.R. Symons, 1986, Investigation of chert heating conditions using ESR spectroscopy. In: The scientific study of flint and chert: Proceedings of the fourth International Flint Symposium held at Brighton Polytechnic, 10-15 april 1983, (Sieveking, G. de G., & Hart, M.B., Eds.), Cambridge University Press, Cambridge: p. 259-262.
Heinen, M., 2005, Sarching ’83 und ’89/90. Untersuchungen zum Spätpaläolithikum und Frühmesolithikum in Südost-Deutschland. Welt und Erde Verlag, Kerpen-Loogh, 520 p. (in German) (“Sarching '83 and '89/90. Studies of the Late Palaeolithic and Early Mesolithic in Southeastern Germany”)
Hurst, V.J. & A.R. Kelly, 1961, Patination of cultural flints. Science, 134(3474): 251-256. doi:10.1126/science.134.3474.251
Inizan, M.-L., H. Roche & J. Tixier, 1977, Avantages d’un traitement thermique pour la taille des roches siliceuses. Quaternaria, 19: 1-18. (in French) (“Benefits of heat treatment for knapping siliceous rocks”)
Keeley, L.H., 1980, Experimental determination of stone tool uses; a microwear analysis. University of Chicago Press, Chicago, 212 p.
Luedtke, B.E., 1992, An archaeologist’s guide to chert and flint. Archaeological Research Tools Vol. 7. University of California, Los Angeles, 172 p.
Mercieca, A. & P. Hiscock, 2008, Experimental insights into alternative strategies of lithic heat treatment. Journal of Archaeological Science, 35(9): 2634-2639. doi:10.1016/j.jas.2008.04.021
Monk, D.J., D.S. Soane & R.T. Howe, 1993, A review of the chemical reaction mechanism and kinetics for hydrofluoric acid etching of silicon dioxide for surface micromachining applications. Thin Solid Films, 232: 1-12. doi:10.1016/0040-6090(93)90752-B
Munsell, Color (company), 1975, Munsell soil color charts. Munsell Color, Baltimore, 4 p.
Olausson, D.S, & L. Larsson, 1982. Testing for the presence of thermal pretreatment of flint in the mesolithic and neolithic of Sweden. Journal of Archaeological Science 9: p. 275-285.
Nadel, D., 1989, Flint heat treatment at the beginning of the Neolithic period in the Levant. Mitekufat Haeven: Journal of the Israel Prehistoric Society, 22: 61-67. URL: http://www.jstor.org/stable/23373091
Purdy, B.A., & H. K. Brooks, 1971, Thermal alteration of silica minerals: an archaeological approach. Science, 173(3994): 322-325. doi:10.1126/science.173.3994.322
Robins, G.V., N.J. Seeley, D.A.C. McNeil & M. R. C. Symons, 1978, Identification of ancient heat treatment in flint artefacts by ESR spectroscopy. Nature, 276: 703-704. doi:10.1038/276703a0
Robins, G.V., N.J. Seeley, M.C.R. Symons & D.A.C. McNeil, 1981, Manganese (II) as an indicator of ancient heat treatment in flint. Archaeometry, 23(1): 103-107. doi:10.1111/j.1475-4754.1981.tb00960.x
Rowney, M. & J.P. White, 1997, Detecting heat treatment on silcrete: Experiments with methods. Journal of Archaeological Science, 24(7): 649-657. doi:10.1006/jasc.1996.0147
Santaniello, F., S. Grimaldi, A. Pedrotti & S. Gialanella, 2016, First evidence of heat treatment during the early Neolithic in northeastern Italy. Quaternary International, 402: 80-89. doi:10.1016/j.quaint.2015.08.006
Schmidt, P., S. Masse, G. Laurent, A. Slodczyk, E. le Bourhis, C. Perrenoud, J. Livage & F. Fröhlich, 2012, Crystallographic and structural transformations of sedimentary chalcedony in flint upon heat treatment. Journal of Archaeological Science, 39(1): 135 144. doi:10.1016/j.jas.2011.09.012
Schmidt, P., V. Léa, Ph. Sciau & F. Fröhlich, 2013, Detecting and quantifying heat treatment of flint and other silica rocks: A new non-destructive method applied to heat-treated flint from the Neolithic Chassey culture, southern France. Archaeometry, 55(5): 794-805. doi:10.1111/j.1475-4754.2012.00712.x
Stapert, D., 1976, Some natural surface modifications on flint in the Netherlands. Palaeohistoria, 18: 7-41.
Tiffagom, M., 1998, Témoignages d’un Traitement Thermique des Feuilles de Laurier dans le Solutréen Supérieur de la Grotte de Parpalló (Gandia, Espagne). Paléo, 10: 147-61. (in French) (“Evidence of heat treatment of laurel leaf points in the Upper Solutrean of the Parpalló cave (Gandia, Spain)”)
Weiner, S., V. Brumfeld, O. Marder & O Barzilai, 2015, Heating of flint debitage from Upper Palaeolithic contexts at Manot Cave, Israel: Changes in atomic organization due to heating using infrared spectroscopy. Journal of Archaeological Science, 54(1): 45-53. doi:10.1016/j.jas.2014.11.023
Zhou, Z.Y., Y. Guan, X. Gao & C.X. Wang, 2013, Heat treatment and associated early modern human behaviors in the Late Paleolithic at the Shuidonggou site. Chinese Science Bulletin, 58(15): 1801-1810. doi:10.1007/s11434-012-5522-3
How to Cite
Kiers, L. (2018). Differential etching after lithic heat treatment: First results of an experimental study. Journal of Lithic Studies, 5(1). Retrieved from http://journals.ed.ac.uk/lithicstudies/article/view/1456