Workshop 1 - Cores and Flakes
This workshop is the first in a series that involves working with 3D models of stone artefacts.
In making a stone tool, the stone-worker, or ‘flintknapper’, strikes flakes from a core. A core is, technically, any stone from which flakes have been removed—this can include cobbles and chunks of stone, or flakes that were struck previously and then further reduced. Most archaeologists, however, refer to flakes that have been further reduced as retouched flakes, or by their typological classification (e.g., ‘Tula Adze’).
Cores with large scars on them are sometimes assumed to be tools (called core tools), or the sources for flakes to be used as tools (called producer cores). This is helpful in communicating about stone tools with other archaeologists, but it assumes ‘intent’ on the part of the past stoneworkers that is difficult to evaluate. Cores can be both tools and sources of blanks for other tools.
This workshop will discuss cores and flakes. Your goal in this workshop is to understand the nature of flake scars and platforms on cores, and the nature of the surfaces and platforms on flakes.
Tip: hit the play button to load the 3D model. You can now rotate the model as you read the text on the left.
Flake Core, Liang Bua Cave
This small core was excavated from Liang Bua Cave, Flores, Indonesia, and was made by the 'hobbit', Homo floresiensis. It is made from metamorphosed volcanic ash, or tuff. The core is heavily reduced.
As you rotate the core, take note of the angular nature of the various surfaces and how they intersect. All of these various facets are flake scars from earlier in the reduction process. One face of the core is ‘domed’ and the opposite face is flat. On the flat face you will see one large, roughly square scar—a scar left from one of the last flakes struck from this core. The hollowed-out area on the scar is the negative bulb of percussion, indicating where the blow was struck.
Note how the flake that produced this scar was removed by striking an adjacent flat facet, which itself is a flake scar. This was the platform surface for striking the flake. Rotate the model around so you can see the angle between this negative flake scar and the platform surface. This angle is acute, or less than 90 degrees, which is a key condition for striking flakes from a core.
You can visualise a lot about the flake from these observations of the core scar—for instance, we know that the flake has a large bulb of percussion, is roughly square-shaped, and has what we call a single-facet platform (the small part of the core’s platform surface that came away with the flake). Note also that the flake cut through a steep facet on one edge of the core—this will be preserved as a right-angle edge on the flake. This is how to look more deeply at stone tools—you should think about what features are on the artefact in front of you, and infer what the missing parts might have looked like.
This core also has several short little scars intruding into the domed side, and ending in steep shelves. In technical lingo, these scars terminated in step fractures. Terminations like these suggest that the flintknapper failed to hit the stone hard enough to drive the crack right through the core. Now rotate the core around and note how each of these blows was struck onto an acute-angled edge, and behind a ridge or lump on the core—the essential elements in stone-flaking.
This large core is made from silcrete, one of the most common stones used for tools in Australia. As you rotate the core, note how most of the flake scars were struck from the relatively flat surface with the ‘Narran Lake’ label. There are a number of large flake scars from blows around the periphery of this flat platform surface, as well as a number of smaller scars that end in step terminations. Note how the platform angle—the angle between the platform surface and the face from which the flakes are struck—is approaching 90 degrees in some places.
What is the flat platform surface on this core? Sometimes cores of this type are made on extremely large flakes, struck from boulders, with more flakes then struck using the large flake’s ventral surface as a platform. There are too few clues on this platform to indicate whether it is a flake blank ventral surface—it may be a natural spalled surface.
Now see if you can find the flake scars struck from other facets on this core, on the core’s ‘base’ (the end opposite the platform). Horsehoof cores often have flakes struck from the base. Sometimes this may have been done to shorten the core face so that flakes struck from the main platform would travel the length of the core, ending in an axial termination. Alternatively, it may have been done to prepare the base of the core to use as a pounding tool (horsehoof core bases often show wear from use as a hammerstone). Several sets of scars are present on this core, from two separate platforms, so this core is technically multiplatform, although the horsehoof type is conventionally referred to as a single-platform core.
Now look at this 3D model of a horsehoof core, also made of silcrete. Note how the overall patterning of the flake scars are very similar between these cores. Both show reduction around the perimeter of one platform surface, with quite a few large scars, and smaller scars intruding into them. Repetition like this is what archaeologists look for in defining ‘types’.
This core is particularly interesting, because a triangular facet on one side does not have any flakes struck from it. This is because the platform angle—the angle between the flat platform and the core face—is more than 90 degrees (rotate the core to see this), thus violating the acute angle rule. The stoneworker knew they could not successfully strike a flake from that surface, and left it unmodified.
This core was flaked very differently from horsehoof cores. The flake scars on one face are very steep and do not intrude very far onto the surface. That surface is composed of the original surface of the stone, called cortex. But on the other side, the scars intrude right across the face.
If you look at these more invasive scars carefully, you can see how they were struck from around the perimeter of the core, and the later scars intrude into the earlier scars. Note how deeply ‘scalloped’ the scars looked—the bulbs of percussion on these flakes were very large and prominent. This indicates that a hard hammerstone was used to strike off these flakes, rather than a soft hammer.
Now turn the core side-on, and examine the platform angles for these larger, more invasive flakes. The platform angles are acute, as you might expect, but the platform surfaces are composed entirely of those non-invasive flake scars removed to the opposite face. Those shorter scars were struck to create the acute platform angle around the periphery, allowing those longer flakes to be struck. It is patterning like this that give us insights into how flintknappers visualised the geometry of stones, and how they strategised their flake removals to manipulate those geometries. Think about how different this core is from the horsehoof cores you examined previously.
The lowest point of a scallop tells you the point where the blow was landed on the platform (the Point of Force Application, or PFA). Rotate the core around and have a look at those PFAs. Some of them were on flat facets created by those short scars, but others are on the ridges (called arrises) between those short scars. What would the platforms look like on the flakes struck from these scars?
Now have a look at this blade core. Note how long and narrow the flake scars are on the face of this core. Flakes that are twice as long as they are wide are called 'blades' by archaeologists, or 'elongated flakes'. In colloquial English we refer to the business-end of a knife as a ‘blade’, but the archaeological term is much more specific. When working with archaeologists, be sure to use the technical definition of the term ‘blade’, not the colloquial one, or everyone will get confused.
Blades were struck from this core using a punch, a technique called indirect percussion. Have a look at the different sorts of flake scars on this core. The elongated blade scars dominate one face, but on the flip-side of the core there are a lot of shaping flakes of various shapes and sizes. Note how the platform for the blade scars is composed of one big curved surface—this is itself a flake scar.
You can also see three wide, short scars on the blades’ platform edge. Removing the stone to create these short scars also made the platform angle steeper, closer to 90 degrees. We know from experiments that this was a technical requirement for successfully striking off the blades. This model is an example of a blade struck from a core similar to this and using an indirect percussion technique.
Consider just how different the various flake scars look across these cores types, and what it might mean for the shapes of the flakes struck from them.
Flake: Levallois Point
We have had a good look at cores and flake scars, so next we will turn to flakes—the pieces of stone that were struck to produce the flake scars.
The flake in this model has one smooth surface, and a flip side composed of ridges. The smooth surface is the ventral side of the flake—the side that fits back onto, or conjoins, the scar left behind on the core. One end of the ventral surface is bulged outward—this is the ‘positive’ version of the bulb of percussion, corresponding with the scooped-out negative versions we looked at on the previous core models.
The apex of the bulb of percussion is the impact point where the crack was initiated—the flake’s Point of Force Application, or PFA. The surface at this end of the flake—the proximal end—is the flake platform: the part of the core platform that came away with the flake. Note that in this case the platform is a mixture of a flat surface and a few small flake scars. Of the cores we examined previously, which one would have been the most likely to have produced a flake with a platform like this?
Now flip the flake over and look at those ridges—this is the dorsal side of the flake. The ridges, or arrises, are the edges of flake scars that were on the core before this flake was struck. Earlier we examined how you can visualise features of a flake from its scar, even without actually having that flake. With flakes, we reverse the process—we can visualise the features of the core by looking at the remnants of negative scars on the dorsal surface of the flake, but without actually having the core.
Note that the configuration of scars on the dorsal surface of the flake are, in fact, the high mass targeted by the flintknapper when they struck the platform. In this case, the high mass was created by—in other words, was ‘set up’ by—the previous flaking.
In the case of Levallois points, the flintknappers created zones of high mass that were more-or-less triangular in shape, by carefully removing prior flakes to shape that high mass. We see those shaping flakes as scars on the dorsal surface of the flake that was then struck from the core. Why would they use that strategy?—the standard explanation for Levallois points is that the flintknappers wanted to make triangular flakes that they could haft onto spears.
This artefact was found on the surface and was exposed for an extensive period of time, possibly tens of thousands of years. Across that immense span of time, the tool’s edges were dinged-up by natural ('taphonomic') processes, such as tumbling and animal trampling. If you look closely, these edge dings are themselves flake scars, but on the whole they lack the patterning we see in deliberate shaping and retouching.
Horsehoof Core Resharpening Flake
This model is a chert flake from northwest Queensland, Australia. Rotate the flake until you find the bulb of percussion on the ventral surface, and put this at the top of the frame, ventral surface facing up. Now rotate the top edge toward you. If you did this correctly, you are now looking right down onto the platform surface. This surface is what archaeologists call a cortical platform, because it is part of the original weathered surface of the natural stone, called cortex.
Now rotate the flake so that the dorsal surface faces out. Have a look at the small flake scars along the platform edge—remember that these were the scars on the core prior to this flake being struck. The scars end in deep step terminations, cutting into the larger scars that were on the core face.
Now think about what that core must have looked like. Does it seem familiar? That is because this flake was struck from a core similar to the horsehoof cores we looked at earlier in this workshop. Aboriginal stone knappers would resharpen cores like those by striking larger flakes through those step-terminated flakes, ‘cleaning off’ the edge of the core, and making it suitable for more use. In this case, archaeologists found the resharpening flake, but not the core, yet the flake tells us that cores like these were used and resharpened at the site.
Flake: Tula Adze
This model is of a chert flake from northwest Queensland, Australia. The flake’s platform is a cortical surface.
Note how the much of the perimeter of this flake was trimmed away by flaking, called ‘retouching’. You can see how the ventral surface of the flake served as the platform for striking off the retouching flakes. The angle between a flake’s ventral and dorsal surfaces is almost always acute, and thus ideal for striking off more flakes. In this case, the flake was carefully trimmed to create a specialised Australian woodworking tool called an ‘adze’.
At the top of the bulb of percussion on the ventral surface of this flake, you will see a hemispherical projection, called the umbo. This is part of the ring crack that was formed when the crack was initiated—similar to the ring crack that forms when your windscreen is hit by a stone. This is the flake’s PFA.
Now look at the dorsal surface of this flake. Note that the high mass is, well, a concavity. This reflects a very unusual stone-flaking method, one known to occur in only three or four parts of the world, which in Australia is called the 'gull wing' technique. By striking behind a concavity, the flintknapper was able to create a more pronounced bulb of percussion. Then the edge is eventually trimmed so that it intersects the bulb, it takes on a U-shaped profile. This profile was ideal for woodworking.
You should now have a basic understanding of what archaeologists are talking about when referring to cores, flakes, and flake scars. Now have a browse through the other 3D models and have a look at the range of variation in flake scars across a variety of stone tools from prehistory.