Fractures in Knapping

This book is for students and practitioners of not only knapping, lithic technology and archaeology, but also of fractography and fracture mechanics. At conferences on fractography of glasses and ceramics, the author has often been asked to demonstrate knapping as well as provide overviews of fractography learned from it. The first part of the book is intended to stimulate such interests further, in order to solicit contributions from a largely untapped pool of experts. Such contributions can advance significantly our understandings of knapping as well as fractography. In Part II of the book, fracture markings as the tools of fractography are introduced, with their formation, meaning and utility explained. Observations on the presence or absence of the markings in knapping are considered in Part III, along with a number of interpretations of fracture features. The basic principles and concepts of fracture mechanics and fractography apply to fractures produced in any cultural context. This volume therefore addresses most questions on fracture in a generic sense, independent of cultural contexts. In general, understanding of fractures provides a sounder basis for lithic analysis, and use of more recent scientific tools opens new avenues for lithic studies. Table of Contents PART I: ELEMENTS OF KNAPPING 1.Knapping Past and Present Introduction Traditional Crafts and Industrial Society Prehistoric Knapping Recent and Remnant Knapping Traditions Some Specialized Knapping Traditions Gunflints Threshing Sledges Ceramic Industry Modern Knapping and Recent Explosion Of Interest Knapping Studies Archaeological Record Ethnography Knapping Experiments Living Archaeology Mechanics, Fracture Mechanics and Fractography Contemporary Crafts 2.Knapping Tools and Techniques Antler and Wood Billets Hammerstones Punches Pressure Flakers Holding and Fabricating Devices Anvils and Supports Hides Grinding and Abrading Stones Nontraditional Tools and Acessories Use-Wear Indicators Direct Percussion Anvil Technique and Anvil Percussion Bipolar Percussion Indirect Percussion Pressure Flaking Pecking, Grinding, Polishing Edge and Platform Preparation Some Rules of Thumb Knappers' Wisdom, Folklore and Dilemmas Softer Percussors and Slower Blows Follow-Through with Forces Ridge Abrasion Wetting and Soaking Learning to Knap 3.Raw Materials Material Selection and Use Obsidian Flint and Chert Other Materials Physical and Mechanical Properties Microstructure and Physical Properties Homogeneity and Isotropy Elasticity, Ductility, Brittleness Elastic Constants Constants for Thermal Effects Strength and Fracture Toughness Mirror Constants Workability Alteration of Properties And Behavior Hydration and Vesiculation of Obsidian Cortex and Patina on Flint and Chert Thermal Cracking Thermal Alteration and Heat Treatment Environmental Effects Procurement Nontraditional Uses of Obsidian, Flint and Chert PART II - FRACTURE MARKINGS: THE TOOLS OF FRACTOGRAPHY 4.An Overview 5. Hackles and Hackle Scars Twist Hackles and Single Tails Multiple Tails Parabolic Double Tails Hackle Scars Hackle Scar and Hackle Flake Bulbar Scar and Proximal Scar Ripple Scars Ridge Scars More on Hackle Scar Formation 6.Ripples Ripples Wallner Lines Normal Wallner Lines Anomalous Wallner Lines Stress Changes Causing Ripples Static Effects Specimen Vibration Stress Pulses Experimental Ripples Ultrasonic Modulation Sonic Modulation Exploding Wire Experiments Terminology and Interpretations by Others 7. Mirror, Mist, Hackle, Branching Mirror Mist and Velocity Hackle Branching, Incipient Branching and Lateral Wedges Velocity and Energy Considerations Mirror Constants and Stresses Markings Related to Mist and Hackle Wallner Mist-Hackle Configuration Mist Suppression Configurations Mist Lines 8.Miscellaneous Markings Material Interface Markings Material Interface Ridges and Ripples Material Interface Hackle Material Transition Ridge Split Marks Dividing Lines Ruffles Liquid-Induced Fracture Markings (Lifms) Effects of Moisture and Liquids Conditions for Manifestation of LIFMs Occurrence of LIFMs Significance of LIFMs Basic Kinds of LIFMs A Catalogue of LIFMs and Patterns Observation of LIFMs Variability with Liquids Variability with Lithic Materials LIFMs with Sonic Modulation LIFMs Observed with Condensation Some Surface Patterns PART III - FRACTURES IN KNAPPING 9.Introduction Elements of a Mechanical System And Knapping Stresses, Stress Waves and Vibrations Some Fundamentals in Fracture Mechanics Catastrophic and Subcritical Crack Growth Research on Fractures in Knapping Other Research 10.Flake Initiations, Proximal and Surface Features Flake Initiations Some Definitions Hertzian Cone Fractures Contact Initiations Non-Contact Initiations Initiations with Multiple Blows Effects of Cortex and "Layering" Environmental Effects Percussor Softness and Speed Proximal Flake Features Platform Characteristics Dorsal Ridges and Curvatures Interior Platform Edge Wing Flakes Bulbs Popouts and Stepouts Flake Surface Features Fracture Directions Ripple Configurations and Fracture Fronts Ripple Concavity Ripples Related to Flake and Core Geometry Ripples at Inhomogeneities Why Ridges Guide Flakes Fracture Velocities Mist and Related Markings Hackle Scars Ruffles Split Marks Tails and Incipient Tails 11.Crack Paths and Flake Profile Features Criteria for Crack Paths Crack Paths and Core Geometry Crack Paths and Forces Applied Popouts and Related Fractures Compression Lips, Curls and Compression Wedges Step-In and Step-Out Fractures Incipient Breaks Popout Fractures Ripple Profiles and Kinks Wavy Crack Paths Flake Terminations "Jacked" Flakes 12.Forces in Knapping Non-Contact Flake Initiations Edge Angle and Core Geometry Location and Direction of Force Application Platform Characteristics Flaw Distributions Flaker Properties Contact Initiations Location of Force Application Direction of Force Application Edge Angle and Core Geometry Platform Characteristics Flaw Distributions Flaker Properties Contact and Non-Contact Flake Initiations: Comparisons Subsequent Detachment Direct Percussion Percussor Characteristics Velocity of Blows Indirect Percussion Punch Characteristics Striker Characteristics Core Mobility Percussion Flaking Pressure Flaking Supports Distal Dorsal Bipolar Percussion 13. Breakage of Blades, Flakes and Bifaces Axial Loads, Bending, Shear, Torsion and Their Effects Clues from Fracture Markings and Other Features Some Fractures with Blades and Flakes Splitting of Blades and Flakes Step-In and Step-Out Fractures Incipient Breaks Popouts Some Fractures with Bifaces Overshots and Edge-to-Edge Flakes Amputations Transverse Breakages Fracture Origins Fracture Directions Compression Lips, Curls and Compression Wedges Mist and Related Markings Branching and Lateral Wedges for Blades and Flakes Fracture Velocities Location of Force Application Some Special Breaks Bowties Slices Segmentation Aztec Appreciation of Mechanics For more than 40 years, Are Tsirk has developed interdisciplinary research on the physical phenomena in knapping, combining his experience in knapping with his longstanding interest in fracture. The work is enhanced by his curiosity and minute observational ability of a natural scientist. It is the most complete monograph on the subject. It will be of interest to all amateurs in knapping and useful, if not indispensible, to fractographers as well as all archaeologists in the study of lithics. Book cover 1 List of Tables 12 Copyright page 3 Contents 3 List of Figures and Tables 9 Preface 13 1. Knapping Past and Present 15 Introduction 15 Traditional Crafts and Industrial Society 15 Prehistoric Knapping 17 Recent and Remnant Knapping Traditions 18 Some Specialized Knapping Traditions 21 Gunflints 21 Threshing Sledges 24 Ceramic Industry 24 Modern Knapping and Recent Explosion Of Interest 25 Knapping Studies 28 Archaeological Record 28 Ethnography 28 Knapping Experiments 28 Living Archaeology 28 Mechanics, Fracture Mechanics and Fractography 29 Contemporary Crafts 29 2. Knapping Tools and Techniques 30 Antler and Wood Billets 30 Hammerstones 30 Punches 32 Pressure Flakers 32 Holding and Fabricating Devices 34 Anvils and Supports 35 Hides 35 Grinding and Abrading Stones 35 Nontraditional Tools and Acessories 35 Use-Wear Indicators 37 Direct Percussion 37 Anvil Technique and Anvil Percussion 38 Bipolar Percussion 39 Indirect Percussion 39 Pressure Flaking 40 Pecking, Grinding, Polishing 41 Edge and Platform Preparation 41 Some Rules of Thumb 42 Knappers’ Wisdom, Folklore and Dilemmas 42 Softer Percussors and Slower Blows 43 Follow-Through with Forces 43 Ridge Abrasion 43 Wetting and Soaking 43 Learning to Knap 43 3. Raw Materials 45 Material Selection and Use 45 Obsidian 45 Flint and Chert 46 Other Materials 47 Physical and Mechanical Properties 49 Microstructure and Physical Properties 49 Homogeneity and Isotropy 49 Elasticity, Ductility, Brittleness 50 Elastic Constants 51 Constants for Thermal Effects 53 Strength and Fracture Toughness 53 Mirror Constants 54 Workability 55 Alteration of Properties And Behavior 58 Hydration and Vesiculation of Obsidian 58 Cortex and Patina on Flint and Chert 59 Thermal Cracking 59 Thermal Alteration and Heat Treatment 61 Environmental Effects 62 Procurement 63 Nontraditional Uses of Obsidian, Flint and Chert 64 4. An Overview 68 5. Hackles and Hackle Scars 77 Twist Hackles and Single Tails 78 Multiple Tails 83 Parabolic Double Tails 84 Hackle Scars 87 Hackle Scar and Hackle Flake 87 Bulbar Scar and Proximal Scar 87 Ripple Scars 88 Ridge Scars 88 More on Hackle Scar Formation 89 6. Ripples 90 Ripples 90 Wallner Lines 93 Normal Wallner Lines 94 Anomalous Wallner Lines 98 Stress Changes Causing Ripples 100 Static Effects 100 Specimen Vibration 101 Stress Pulses 101 Experimental Ripples 102 Ultrasonic Modulation 102 Sonic Modulation 103 Exploding Wire Experiments 104 Terminology and Interpretations by Others 104 7. Mirror, Mist, Hackle, Branching 106 Mirror 106 Mist and Velocity Hackle 106 Branching, Incipient Branching and Lateral Wedges 109 Velocity and Energy Considerations 110 Mirror Constants and Stresses 111 Markings Related to Mist and Hackle 112 Wallner Mist-Hackle Configuration 112 Mist Suppression Configurations 113 Mist Lines 114 8. Miscellaneous Markings 117 Material Interface Markings 117 Material Interface Ridges and Ripples 117 Material Interface Hackle 117 Material Transition Ridge 119 Split Marks 120 Dividing Lines 121 Ruffles 121 Liquid-Induced Fracture Markings (Lifms) 122 Effects of Moisture and Liquids 122 Conditions for Manifestation of LIFMs 124 Occurrence of LIFMs 124 Significance of LIFMs 126 Basic Kinds of LIFMs 126 A Catalogue of LIFMs and Patterns 128 Observation of LIFMs 130 Variability with Liquids 137 Variability with Lithic Materials 137 LIFMs with Sonic Modulation 138 LIFMs Observed with Condensation 138 Some Surface Patterns 138 9. Introduction 140 Elements of a Mechanical System And Knapping 140 Stresses, Stress Waves and Vibrations 142 Some Fundamentals in Fracture Mechanics 142 Catastrophic and Subcritical Crack Growth 144 Research on Fractures in Knapping 145 Other Research 148 10. Flake Initiations, Proximal and Surface Features 150 Flake Initiations 150 Some Definitions 150 Hertzian Cone Fractures 150 Contact Initiations 154 Non-Contact Initiations 161 Initiations with Multiple Blows 162 Effects of Cortex and “Layering” 164 Environmental Effects 165 Percussor Softness and Speed 165 Proximal Flake Features 166 Platform Characteristics 166 Dorsal Ridges and Curvatures 167 Interior Platform Edge 168 Wing Flakes 171 Bulbs 171 Popouts and Stepouts 173 Flake Surface Features 173 Fracture Directions 173 Ripple Configurations and Fracture Fronts 174 Ripple Concavity 174 Ripples Related to Flake and Core Geometry 175 Ripples at Inhomogeneities 176 Why Ridges Guide Flakes 177 Fracture Velocities 178 Mist and Related Markings 178 Hackle Scars 179 Ruffles 179 Split Marks 179 Tails and Incipient Tails 179 11. Crack Paths and Flake Profile Features 181 Criteria for Crack Paths 181 Crack Paths and Core Geometry 181 Crack Paths and Forces Applied 182 Popouts and Related Fractures 182 Compression Lips, Curls and Compression Wedges 182 Step-In and Step-Out Fractures 185 Incipient Breaks 189 Popout Fractures 189 Ripple Profiles and Kinks 195 Wavy Crack Paths 196 Flake Terminations 197 “Jacked” Flakes 199 12. Forces in Knapping 200 Non-Contact Flake Initiations 201 Edge Angle and Core Geometry 202 Location and Direction of Force Application 203 Platform Characteristics 203 Flaw Distributions 203 Flaker Properties 204 Contact Initiations 204 Location of Force Application 204 Direction of Force Application 204 Edge Angle and Core Geometry 205 Platform Characteristics 205 Flaw Distributions 205 Flaker Properties 206 Contact and Non-Contact Flake Initiations: Comparisons 206 Subsequent Detachment 206 Direct Percussion 209 Percussor Characteristics 209 Velocity of Blows 209 Indirect Percussion 209 Punch Characteristics 209 Striker Characteristics 211 Core Mobility 212 Percussion Flaking 212 Pressure Flaking 212 Supports 212 Distal 212 Dorsal 213 Bipolar Percussion 213 13. Breakage of Blades, Flakes and Bifaces 215 Axial Loads, Bending, Shear, Torsion and Their Effects 215 Clues from Fracture Markings and Other Features 215 Some Fractures with Blades and Flakes 216 Splitting of Blades and Flakes 216 Step-In and Step-Out Fractures 216 Incipient Breaks 216 Popouts 217 Some Fractures with Bifaces 221 Overshots and Edge-to-Edge Flakes 222 Amputations 224 Transverse Breakages 225 Fracture Origins 225 Fracture Directions 228 Compression Lips, Curls and Compression Wedges 229 These features are characteristic of breakage by bending (Fig. 11.1). Their formation is discussed in Chapter 11. The characteristic dimensions of the compression lips, curls and compression wedges are observed to vary significantly. The length of a compr 229 Mist and Related Markings 230 Branching and Lateral Wedges for Blades and Flakes 237 Fracture Velocities 238 Location of Force Application 238 Some Special Breaks 238 Bowties 238 Slices 240 Segmentation 242 Aztec Appreciation of Mechanics 244 Concluding Remarks 246 Glossary 248 References 257 Index 273 Fig. 1.2 A Solutrean laurel leaf from Volgu, France. The cast is 27.4 cm long and about 7 mm thick. (The photo is of a cast from the Museum of Man in Paris.) 17 Fig. 1.3 A Paleoindian Clovis Point from Blackwater No.1 Site. 10.6 cm long. The arrow indicates a fracture marking known as a split ridge (Chapter 8), seen poorly. (Photo is of Bostrom’s plastic cast by Kristian Mets.) 18 Fig. 1.4 Replica of an Egyptian Predynastic Gerzian knife. Flint, 25.2 cm long.(Kelterborn 1984. Reproduced with permission) 18 Fig.1.5 Type IV-E Danish dagger. Errett Callahan’s replica of the famous Hindsgavl Dagger. Flint, 29.3 cm long. (Callahan 1999, reproduced with permission) 19 Fig. 1.6 Type IC Danish dagger. Replica by Greg Nunn. An excellent example of edge-to-edge flaking. It broke during final retouch. Flint, ca 26 cm long. (Nunn 2006, reproduced with permission.) 20 Fig. 1.7 Replicas of Neolithic square section axes of Denmark by Thorbjorn Petersen (Courtesy of Errett Callahan. Photo by Jack Cresson). 21 Fig. 1.8 An exhausted blade core on the gunflint knappers work floor at Brandon. 22 Fig. 1.9 Threshing sledges in Turkey. The one at the right, as well as the partly seen sloping one at the left, has two wide blanks. The lower two photos show the details of the flint blade inserts. These were in a “coffee shop” in the tourist section of 23 Fig. 1.10 Knapped blocks at Eben-Emaël for porcelain industry. Squared blocks for end of the mill. (Callahan 1985. Reproduced with permission.) 25 Table 3.1 Major Constituents in Obsidians 47 Table 3.3 Constants for Thermal Effects 54 Table 3.4 Examples of Fracture Toughness 55 Fig. 3.1 Callahan’s proposed lithic grade scale (Callahan 1979, reproduced with permission) 56 Fig. 3.2a Workability vs. K1c 57 Fig. 3.2b Fracture Toughness vs. Lithic Grade 57 Fig. 3.3 Potlid fractures: At the bottom of the center column is a potlid fracture on which a secondary one (shown above it) occurred at its inner surface. A potlid fracture with the associated potlid is shown in the right column. 60 Fig. 3.4 A frost pitted nodule of Cobden chert. 61 Fig. 3.5 Sinuous fracture of a chert biface due to cooling too fast. Burlington chert from Crescent Quarry. 62 Fig. 3.6 A modern Normanskill chert quarry in Greene County, New York. The chert and the parent shale are used in contemporary construction. The scale of the operation is seen by the construction equipment in the background. The nodules and boulders seen 65 Fig. 3.7 Use of flint for houses in Brandon, England. The Bell on the top left, presently an inn, has untrimmed flint nodules in the wall. The brick house on the right uses trimmed flint as decoration in the brickwork. It used to belong to the gunflint kn 66 Table 4.1 Fracture Markings Terminology 69 Table 4.2 Occurrence of Fracture Markings 71 Table 4.3 Utility of Fract ure Markings 72 Table 4.4 Clues from Fracture Markings 74 Table 4.5 A Catalogue of Fracture Markings 74 Fig. 5.1 Tails (as at A and B) and twist hackles as persistent tails (black arrow) in obsidian. The mist and hackle at the right (white arrow) is at the lip of a biface thinning flake. The gull wings indicate a very high fracture velocity. At B, the appro 77 Fig. 5.2 Formation of twist hackles 78 Fig. 5.3 Twist hackles at the edge of an obsidian flake. A number of smaller ones are seen to merge into a larger one, as at the arrow. Fracture direction is downward to the right. 79 Fig. 5.4 Twist hackles at and near the edge of a biface thinning flake of a fine variety of Normanskill chert. The general fracture direction for the flake was downward. 79 Fig. 5.5 Twist hackles and incipient twist hackles in a coarse variety of Normanskill chert. The characteristics of these markings are influenced by their angle with the general fracture direction (downward here) for the flake, as well as the size and nat 80 Fig. 5.6 Twist hackles (arrow) and incipient twist hackles (especially in b) in Esopus chert. 81 Fig. 5.7 Tails in obsidian often persist as twist hackle. The “flip-flop” by the arrow is due to the lateral breakthrough to one and then the other side. The fracture direction was downward. 82 Fig. 5.8 Tails at irregular inclusions in obsidian, formed by the fracture passing around and through the inclusion. 82 Fig. 5.9 Parabolic double tails, formed as the fracture passes through the inclusion at its head, onto a different plane. Note the third tail in (c). Obsidian. Fracture direction downward. 85 ig. 5.10 Parabolic double tails and many mist lines on the surface of a flake. Glass Buttes obsidian. Fracture direction downward. (Photo by V.D. Fréchette; from Tsirk 1996) 86 Fig. 5.11 Parabolic double tails in a mist region. The fracture in the Jemez Mountains obsidian was caused by a forest fire at an archaeological site (Steffen 2005). 87 Fig.5.12 Convergent tails with trailing mist line. Obsidian. Fracture direction downward. 88 Fig. 5.13 Hackle scars at the edge of an obsidian flake. On the left portions of the figure, the fracture direction was downward. 89 Fig. 5.14 An overshot hackle flake and its scar on an obsidian flake. 89 Fig. 6.1 Stress changes associated with ripple formation 90 Fig. 6.2 Ripple profiles and associated changes in shear stress. 91 Fig. 6.3 Gull wings at numerous inclusions on a flake. Wallner wakes are barely seen at the arrows. Glass Buttes obsidian. Fracture direction downward. Width of field 1.8 mm. (From Tsirk 1988) 95 (From Tsirk 1988) 96 Fig. 6.5 Formation of gull wings 97 Fig. 6.6 “Knappers’ Speedometer” 97 Table 6.1 Errors (%) in VF/VS due to rotation of fracture plane 98 Fig. 6.7 Wallner wake formation. (From Tsirk 1988) 99 Fig. 6.8 An obsidian flake detached by percussion with ultrasonic modulation at 175 kHz. Fracture direction downward. (Courtesy M.G. Schinker for the modulation) 102 Fig. 6.9 Sonic modulation (at 183 Hz) used on an obsidian pressure flaker. The fracture is propagating upwards at about 2 to 3 cm/s. The dry parts (as at arrows) are lagging behind the leading wetted parts. The image width is ~2.8 mm. 103 Fig. 7.1 Breaking stresses and mirror radii 106 Fig.7.2 Mist (dashed arrow) and hackle (solid arrow) on an accidental break of a biface. The tensile face of the biface is at the right. Mist lines and narrow, parabolic doube tails are seen in the lower part of the mist region. Glass Buttes obsidian. Fra 107 Fig. 7.3 Fracture surface of an accidental break from an internal flaw. Mist (dashed arrow in a) and hackle (solid arrow) are clearly seen in the obsidian. 108 Fig. 7.4 A mist-hackle configuration (arrow) in a mist region in obsidian. Fracture direction is downward. 113 Fig. 7.5 Mist line in obsidian Fracture direction downward. 114 Fig. 7.6 Mist and hackle patterns. Mist lines in lieu of tails and twist hackles are manifested close to the general mist regions. Mexican obsidian. The fracture origin was near the top. The downward fracture direction is indicated by the mist lines. 115 Fig. 8.1 Material interface ridges (solid arrow) and material transition ridges (dashed arrow) in obsidian. 118 Fig. 8.2 Formation of a material interface ridge. 119 Fig. 8.3 Split marks on a flake. Split step (dashed arrow) and split ridge (solid arrow) are seen. 120 Fig. 8.4 Ruffles on the inner surface of an obsidian flake due to geometrical irregularities on outer surface. (From Tsirk 2012) 122 Fig. 8.5 Variation of fracture velocity VF with stress intensity factor KI for dry, moist and wet environments for a glass 123 Table 8.1 Basic Types of LIFMs (by Appearance) 125 Fig. 8.6 The basic LIFM type called an escarpment scarp (arrow) on an obsidian pressure flake with the platform wetted with water. Fracture direction upward. 126 Fig. 8.8 The basic LIFM type called linear band features (arrows). Obsidian pressure flake. Platform wetted with water. Fracture direction upward. 127 Fig. 8.7 The basic LIFM type called a liquid-induced hackle (arrow). The platform was wetted with saliva for the obsidian pressure flake. Fracture direction upward. 127 Fig. 8.9 The basic LIFM type called a cavitation scarp (arrow) on an obsidian pressure flake. Platform wetted with water. Fracture direction upward to right. (Adapted from Tsirk 2001.) 128 Fig. 8.10 Two unusual encounter-depletion scarps. Obsidian, wetted with saliva. Fracturing upward. The upstream part of each scarp is an encounter scarp (arrow). 129 Fig. 8.11 Sierra scarps in a soda-lime glass plate broken accidentally in a sink with liquid. Fracture direction is up to the right. The upstream shoulders are encounter scarps, partly with escarpments (arrow) and partly with hackle scarps (dashed arrow). 130 Table 8.2 Liquid-Induced Fracture Markings (LIFMs) 131 Fig. 8.13 Miscellaneous scarps. Most prominent are the encounter-depletion scarps manifested in the form of fingerlets. Obsidian, wetted with saliva. Fracture direction upward. 135 Fig. 8.12 An encounter scarp (arrow) manifested as a hackle scarp. Obsidian, wetted with water. Fracture direction upward. 135 Fig. 8.14 Depletion scarps manifested as irregular fingerlets. Obsidian, wetted with blood. Such irregular fingerlets were never seen with water or saliva. Fracture direction upward to the right (Adapted from Tsirk 2001.) 136 Fig. 8.15 Occurrence of scarps with distance from the fracture origin on pressure flakes of obsidian. 136 Fig. 8.16 The very many inclusions of variable sizes in this pressure flake of industrial waste glass rendered the LIFMs (arrow) particularly conspicuous. Water used for wetting. General fracture direction upward. 138 Fig. 8.17 The very many inclusions of variable sizes in the industrial waste glass led consistently to manifestation of very unusual and conspicuous LIFMs over the whole surface. Water used for wetting. General fracture direction upward. 139 Fig. 8.18 Sonic modulation at 183 Hz was used for this obsidian pressure flake wetted with water. The encounter scarp (arrow) is formed when water becomes available from the right side. From the configurations of these Wallner lines, it is seen that water 139 Table 10.1 Flake Initiations 151 Fig. 10.1 Hertzian cone fracture. 152 Fig. 10.2 Force vs. time for several impact velocities and sphere radius R = 5.1 cm.. 153 Table 10.2 Hertzian Cone Fractures and Hertzian Flake Initiations: Some Differences 155 Fig. 10.3 Flake initiation by wedging in Normanskill chert: Solid arrow in both cases indicates a split cone or other contact feature. In contrast to the pronounced ripples in (a), the ripples in the more confined flat region in (b) (dashed arrow) are sub 155 Fig. 10.4 Flakes with Hertzian initiation in Normanskill chert: (a) A cone-like feature with ripples. A ring crack is present on the platform. Proximal width is 5.7 cm. (b) There are the proximal ripples but no cone-like feature and no ring crack. The He 156 Fig. 10.5 Flake with Hertzian initiation. The cone-like feature has pronounced “step ripples”. Flake is 6.4 cm long at mid-section. Normanskill chert. 157 Fig. 10.6 Combined wedging-Hertzian initiations. The solid arrow indicates a partial cone-like or other Hertzian feature. The dashed arrow points to the “split” part of this feature. Nearly flat regions with ripples resembling circles are manifested in bo 158 Fig. 10.8 A wing flake can drastically alter the edge angle for subsequent flaking, as seen in (b). A flake scar (2.6 cm wide) and wing flake scars are seen in (a). These are for the wider face of a square section axe. 160 Fig. 10.7 A flake with a wing flake that was detached to the left side. Solid arrow shows the location of the Hertzian flake initiation; dashed arrow, the twist hackle from which the wing flake originated. Moose antler punch used. Texas flint. 160 Fig. 10.9 Flake initiation by unzipping. The arrow in (a) corresponds to the arrow at C in (b). The core platform was struck a number of times with a very hard hammerstone, roughly along the line of the prospective flake edge. The biggest Hertzian contact 163 Fig. 10.10 Grinding over pecking on a platform of an Aztec blade from Otumba site in Mexico. The enlarged view in (b) is of the lower left part of (a). Pachuca obsidian. 165 Fig. 10.11 Schematic outlines for cross-sections of a square section axe. For flake removal from the short face AB, it is advantageous or even necessary to apply the force in the direction shown in (a). If the force is applied as in (b), the flake will te 167 Fig. 10.12 Mist and hackle at the lip by the right edge of an obsidian biface thinning flake with bending initiation. 169 Fig. 10.13 Proximal region of the same flake (adjacent to its platform) produced by direct percussion, having a bending initiation. A mist-hackle region adjacent to the edge is conspicuous, especially in (a). These regions characteristically occur when th 170 Fig. 10.14 A hackle scar on a bulb, with the associated overshot hackle flake. 173 Fig. 10.15 Variations of flake thickness in transverse direction affecting the fracture front and ripple configuration. In (b), it is partly concave in the downstream direction. (Adapted from Tsirk 1981.) 175 Fig. 10.16 These ripple configurations relate to the variations in flake thickness in the transverse direction. (a) and (b) are obsidian. (c) is Normanskill chert. (a and b adapted from Tsirk 2012: Fig 7) 176 Fig. 10.17 Material interface markings: Material interface ripple in (a) and material interface ridge in (b). 177 Fig. 10.18 Split marks: Split step (solid arrow) and split ridge (dashed arrow). Esopus chert. 180 Fig. 11.1 Popout and related fractures (schematic): (a) Popout fracture; (b) Stepout fracture; (c) Compression lip; (d) Compression wedge. (Adapted from Tsirk 2010b) 183 Fig. 11.2 Nominal stress trajectories for bending of an uncracked (a) and partly cracked (b) specimen (Adapted from Tsirk 2010b). 184 Fig. 11.3 Effect of shear on the direction of the compression lip: (a) cantilever beam with shear; (b) direction of the compression lip with the shear shown; (c) effect of the shear stress at an element just ahead of the crack tip. (Adapted from Tsirk 201 185 Fig. 11.4 Regular popout fractures with and without a roll-in from a hackle scar. (Adapted from Tsirk 2010b) 186 Fig. 11.5 Formation of a stepout fracture: (a) initial stepout phase with crack extending outward (case with no roll-in); (b) forces causing the stress at B by the unbroken ligament, (c) a completed stepout fracture. (Adapted from Tsirk 2010b) 187 Fig. 11.6 Schematic profiles and fracture directions for popout and stepout fractures observed. (Adapted from Tsirk 2010b) 188 Fig. 11.7 Incipient, quasi-stepout and quasi-popout fractures: The kinked profile of the primary fracture in (a) resembles a stepout fracture. The primary fracture profile in (b) has some resemblance to a popout fracture. With the part-through transverse 190 Fig. 11.8 Partial profiles of obsidian blades with dorsal concavities for (a) popout fractures and (b) stepout fractures. (Adapted from Tsirk 2010b) 190 Fig. 11.9 Regular but unusual popout fractures from percussion, all initiating from a single hackle scar in obsidian: (a) a popout fracture on a very thick flake; (b) a very long (74 mm) popout; (c) a thick flake with a massive popout; (d) a double-sided 192 Fig. 11.10 Reverse (a and c) and compound popouts. (c) shows a reverse popout and stepout combination. All are obsidian, by direct percussion. (Adapted from Tsirk 2010b) 193 Fig. 11.11 Double popouts. Note the compression wedge from which the regular and reverse popouts initiate. The dashed arrows indicate the fracture direction. (Adapted from Tsirk 2010b) 193 Fig. 11.12 Formation of popout fractures. (Adapted from Tsirk 2010b) 194 Fig. 11.13 Popout fracture on an obsidian biface thinning flake (Max. width ~8cm) After a study of many popouts and other fracture specimens, it became apparent that intrusive hackle flakes (with hinge terminations) gradually ”evolve” into popout fracture 194 Fig. 11.14 Comparison of intrusive hackle scars (a and b) with single-sided popout fractures (c to f) from direct (a,b,c) and indirect (d,f) percussion. (d) is Normanskill chert, others are Glass Buttes obsidian. (Adapted from Tsirk 2010b) 195 Fig. 11.15 Flake terminations 198 Fig. 12.1 Wedge loaded at its tip: (a) A force applied parallel to its median plane; (b) A force applied normal to its median plane; (c) Moment applied. 200 Fig. 12.2 Wedge with a force applied in an arbitrary direction at distance e from its tip. 201 Table 12.1 Normalized Force Variations with Wedge Angle 202 Table 12.2 Force Variations with Distance from Edge (r/e) 203 Table 12.3 Comparisons for Contact and Non-Contact Flake Initiations 205 Fig. 12.3 A two-dimensional model for analysis of blade detachment forces subsequent to the initial phase. 207 Fig. 12.4 Variation of forces with lengths of the detached part of the flake. 208 Table 12.4 Properties of Some Woods 210 Table 13.1 Dimensions (mm) of flakes with popout fractures 217 Table 13.2 Nondimensional popout characteristics 218 Fig. 13.1 Broken bifaces from the Caradoc Site, from the late Paleo-Indian ritual artifact deposit. Bayport chert. (From Fig. 2.8 in Ellis and Deller 2002, with permission) 220 Table 13.3 Biface breakages considered 221 Fig. 13.2 A Normanskill chert biface broken accidentally during manufacture. It is surprising that the flake (top) is unbroken. It started out as a thinning flake from the base (See the sketch). Then a crack from the bending break of the biface extended u 221 Fig. 13.3 Overshot (white arrow) flakes on a Clovis preform from Blackwater No.1. One of these was split, as barely seen by the split ridge (black arrow). (Photo of plastic cast by Kristian Mets) 222 Fig. 13.4 Biface with a laterally overshot flake, ruined by the transverse biface break at the location of the overshot. Normanskill chert, direct percussion. Actual size. 223 Fig. 13.5 Biface with a longitudinally overshot flake. Obsidian, direct percussion. Actual size. 223 Fig. 13.6 Schematic illustration of an amputation from direct percussion (to the upper end in Sect. A-A). Tension is at the top surface (in Sect. B-B), as indicated by the mist-hackle and by the compression lip. The fracture direction is shown by the arro 224 Fig. 13.7 Blade detachment with (a) single and (b) double curvature bending deformation. (Adapted from Tsirk 2009) 226 Fig. 13.8 Stresses in a blade with triangular cross-section from a bending moment M. 226 Fig. 13.9 Geometrical properties of triangular, trapezoidal and rectangular sections 227 Fig. 13.10 Examples of fracture fronts (dashed lines) and fracture directions normal to them. Obsidian. Fracture direction downward. Flake in (b) 9.7 cm long and 2.7 cm wide. ((a) adapted from Tsirk 2012) 229 Table 13.4 Lateral Wedges and Branching Cracks on Biface Tensile Surface 231 Table 13.5 Observation of Mist, Hackle, Mist Lines and Parabolic Double Tails on Biface Breakages (No. & [% of Bifaces]) 231 Fig. 13.11 Mist and hackle at a transverse biface break from bending in direct percussion. Normanskill chert of medium grade. (a) More mist is seen at the upper part, closest to the tensile face. (b) is to the right of (a). Mist (left) and (velocity) hack 233 Fig. 13.12 Mist and hackle (arrows) on a section of a prehistoric flint blade from the 9th millennium B.C. In addition to the mist-hackle by the tensile face at the top, an intrusive mist pattern is also manifested at the interior (dashed arrow). An unusu 234 Fig. 13.13 Mist and hackle at a transverse biface break from bending. Normanskill chert of medium grade. (a) More mist is seen at the upper part, closest to the tensile face. (b) is to the right of (a), and (c) is to the right of (b). Hackle seen as the m 235 Fig. 13.15 Mist patterns at the downstream faces of the slices seen in Fig. 13.16 236 Fig. 13.14 Some types of mist patterns 236 Fig. 13.16 Multiple blade breaks with two slices. Obsidian. 237 Fig. 13.18 A pair of lateral wedges on a Cobden Chert biface, broken accidentally during manufacture. 239 Fig. 13.17 Bowtie from blade breakage. Heat treated Arkansas novaculite. Twice actual size. 239 Table 13.6 Observed obsidian slices 240 Fig. 13.19 Slice formation with loss of contact. 241 Fig. 13.20 Slice in biface breakage. Direct percussion with antler billet while end supported on thigh, apparently too lightly. Glass Buttes Obsidian 243 Fig. 13.21 Moment reduction vs. blade geometry when starting a crack from the outer face. 245 Prehistory,knapping,cores,flints,stone tools,manufacture