- Marks left by the blade of a plough. When used on an edge under heavy pressure in a laying or cutting press, a well-set-up plough with a properly sharpened blade is unlikely to leave any marks on the edge, but the area of the head- and tail edges of a bookblock close to the spine could not be heavily compressed because of the swelling caused by the sewing thread. The plough blade was therefore likely to leave parallel marks in this slightly spongy area of the bookblock as it was passed backwards and forwards over the edge. When the bookblock expanded slightly as it was taken out of the press and perhaps had the spine reshaped for the attachment of boards, the straight, parallel plough marks would become curved, often in a pattern of parallel, curved lines converging towards the centre of the spine. The distance between each line will indicate the width of each cut by the plough. In some examples the curved lines can extend further along the edge, indicating that the bookblock edge was in some way deformed in the laying press, and when taken out and straightened up, bent the plough marks into long, curved lines.
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