easier to obtain straight edges. When analysing a hand axe made from a flake, it should be remembered that its shape was predetermined (by use of the Levallois technique or Kombewa technique or similar). Notwithstanding this, it is necessary to note a tool's characteristics: type of flake, heel, knap direction. The natural external cortex or rind of the tool stone, which is due to erosion and the physical-chemical alterations of weathering, is different from the stone's interior. In the case of chert, quartz or quartzite, this alteration is basically mechanical, and apart from the colour and the wear it has the same characteristics as the interior in terms of hardness, toughness etc. However, flint is surrounded by a limestone cortex that is soft and unsuitable for stone tools. As hand axes are made from a tool stone's core, it is normal to indicate the thickness and position of the cortex in order to better understand the techniques that are required in their manufacture. The variation in cortex between utensils should not be taken as an indication of their age. Many partially-worked hand axes do not require further work in order to be effective tools. They can be considered to be simple hand axes. Less suitable tool stone requires more thorough working. In some specimens the cortex is unrecognisable due to the complete working that it has undergone, which has eliminated any vestige of the original cortex. Types It is possible to distinguish multiple types of hand axe: Uniface—flaked on one face with cortex completely covering the other side. This characteristic does not disqualify such tools as hand axes and gives no indication of their age. Partial biface—The cortex is present on the tool's base and central part. The overall area that is not knapped may extend to up to 2/3 of its length. Bifaces with basal cortex coverage—Only the artefact's base is covered with cortex, which does not cover more than a third of total length. In some cases the cortex is present on both the base and one side, thereby affecting one edge: such tools are called "natural backed". De Mortillet emphasised the importance of the presence or absence of the cortex around the edge in the 19th century: "Even on some of the best worked pieces it is common to see, sometimes on the base but more often on the side, a small area that has not been