Sorting and cutting slate

Every slate quarry has its own characteristics as regards accessibility, the angle of layers, and splitting. In particularly favourable locations the layers are separated by a thin fatty layer, which makes extraction very simple. In the traditional method, splitting is carried out directly on the exposed shelves within the quarry. In industrial extraction larger pieces are split with a hydraulic hammer and then transported for further splitting.

The secondary working of slate is usually carried out close to its place of extraction. Even at this stage, each slate has its own characteristics and requires its own particular working methods. Slate is typically a material that requires manual labour; machines are not very useful for processing it.

Generally slates should be no thinner than 6 mm, although this varies with type. Thin slates are easily broken during transport. Once laid on either a floor or a roof, slates will not support high impacts.

If slate is struck in the direction of its layers, straight or curved, the structure of the stone is crushed to a certain depth inwards and the stone divides itself. Pouring water over the slate makes the job easier. During one working day a craftsman with a hammer could produce 60 to 80 slates. With the introduction of slate 'scissors' (see Figure 7.4) which has dominated production since the turn of the nineteenth century, the number went up to 400 slates a day. A small wooden block is used to position notches for the fixing nails, which are knocked out with a pick hammer or cut out with an angle grinder. The working bench is a trestle with slate lying on it. It is possible to knock two slates at the same time.

Slate 'scissors'. One piece at a time Is cut from the edge Inwards to the predetermined point.

Slate 'scissors'. One piece at a time Is cut from the edge Inwards to the predetermined point.

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