The factors governing the strength of leather include the area of the skin which is involved, the part of the animal from which it is taken and the animal breed. A split skin is weaker because it comes from the layer below the grain. The fibre direction in the skin is in the same direction as the hair growth. Fibre direction also governs leather strength - leather is stiffer across the fibres, and stretches more in a direction at right angles. Methods of tanning and processing used can make a difference in the leather properties obtained. Some examples are given and conservators are urged to make more use of such properties. Animal breed is not easy to determine in leather samples, but animal age has more influence than breed on fibre strength. Modern processing (after 1850) dehairs skin on the outside only. Older techniques removed hair even from the follicles. This information could be used to date the approximate period of manufacture.