Retouch (lithics)

Retouch is the act of producing scars on a stone flake after the ventral surface has been created. It can be done to the edge of an implement in order to make it into a functional tool, or to reshape a used tool. Retouch can be a strategy to reuse an existing lithic artifact and enable people to transform one tool into another tool. Depending on the form of classification that one uses, it may be argued that retouch can also be conducted on a core-tool, if such a category exists, such as a hand-axe.

Retouch may simply consist of roughly trimming an edge by striking with a hammerstone, or on smaller, finer flake or blade tools it is sometimes carried out by pressure flaking. Other forms of retouch may include burination, which is retouch that is conducted in a parallel orientation to the flake margin. Retouch is often taken as one of the most obvious features distinguishing a tool from a waste by-product of lithic manufacture (debitage).

The extent of reduction, also known as the retouch intensity, is denoted by a measure of the reduction index. There are many quantitative and qualitative methods used to measure this.

There are three indices of retouch that offer significant inferential power in determining the amount of mass lost in the process of retouching. Despite particular weaknesses associated with each method, the following methods have been shown to be the most robust, versatile, sensitive, and comprehensive.

This method uses measurements of flake thickness and the height of retouch scars to produce a ratio between 0 and 1 of the index of reduction. In the original publication on GIUR by Kuhn (1990), scars are measured at three points (t) along the retouched edge (usually at proximal, medial, and distal points) and then divided by the overall thickness (T) to produce this ratio. The equation is GIUR= ((t1+t2+t3)/3)/T. However, scholars have recently revised Kuhn's methods by measuring T at each point t is measured. The updated calculation is GIUR= (t1/T1+ t2/T2 + t3/T3)/3. The new method creates more data points and may erase biases caused by high variation in artefact thickness. Typically, higher GIUR values indicate more invasive or extensive retouch. Calipers can be used to measure the height of the retouch scar or a goniometer can be used to measure the angle of the retouch and the height can be calculated with the equation t=D sin(a), where "D" is scar length and "a" is angle of retouch. Limitations of the GIUR are its restriction to use on unifacially retouched flakes and that as values increase, they are less able to accurately represent mass loss, because once retouch meets or succeeds the dorsal spine, t/T ratios decline

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