© Header: Markus Kohz
The hand mould is the heart of Johannes Gutenberg’s invention and the only part of the printing process for which he could not fall back on any existing model. It consists of a two-part rectangular hollow metal mould with a channel for filling the liquid metal alloy. The mould is surrounded by a wooden frame so that the instrument can be held in the hand when pouring the hot metal alloy. The matrix is clamped at the lower end of the casting channel and fixed with a metal spring. The matrix can be adjusted according to the type size and width. Now everything is ready for casting the type.
We do not know the composition of Gutenberg’s original alloy, but it can be reconstructed by later descriptions. It consisted largely of lead, to which tin and antimony were added, and very little copper and iron. The advantage of this mixture is that it becomes solid and cold immediately after being filled into the hand mould and the cast sort can be removed directly. In this way it was possible to produce many identical pieces of type in quick succession.
If you remove the pieces of type from the hand casting instrument, they still have an excess piece of metal at the upper end. This part is knocked off at the predetermined breaking point provided for it. The pieces of type are then carefully filed to the correct height so that all of them have the same height at the end. This is important in order to obtain an evenly printed text. Because if one piece of type is too high in relation to the others, it presses too hard into the paper, if it is too low, its letter will not print properly. You can read more about the type and how it is stored in the type case in part 3 of our series “Gutenberg’s inventions”.