|From Paul Kersten's Die Buchbinderei und das Zeichnen des Buchbinders ... (Halle a.d. Saale, 1909), plate 1.|
So, how was this tool used? After sewing on raised or recessed cords, and the spine pasted up, the cords were cut short and pulled through the holes in the blech (tin), untwisted and then frayed out until very fine using the back of a knife. This then allowed them to be pasted out and neatly fanned out on the wastesheet of the textblock or on the top of the board as in the diagram below from Wiese's Werkzeichnen für Buchbinder..., (Stuttgart, 1937).
About this method of board attachment, Ernst Collin wrote in his Pressbengel (translated as The Bone Folder):
BIBLIOPHILE: Master, your logic is impeccable and I will keep what you said in mind. Let me ask you another question. A librarian acquaintance of mine once said that the French do a much better job with their quarter-leather bindings than the Germans.
BOOKBINDER: That is absurd. What is most likely behind that statement is the difference between the French and German styles in how the boards are attached. Remember how I described pasting the frayed-out cords on the board to attach it? What the French do is lace the cords through the boards to secure them. Here, let’s see what Paul Kersten wrote in his Exaktem Bucheinband: “It is commonly believed that a book in which the boards are attached in the French manner is more durable than one in which the German method is used. This is false. The boards are attached to the text block via the cords, and in all cases the failure was at the hinge and after many years of use, not because the boards were not laced on…” (Note: Kersten, Paul. Der Exakte Bucheinband. Halle (Saale): W. Knapp, 1923. Pages 22-23.)
BIBLIOPHILE: Again, I can’t argue with knowledge and experience of a true craftsman like you.
[Edit: See also my follow-up post on the topic]