This piece of millboard was used by Turner, who began a sketch on the other side. We are showing it here as an example of the sort of board that William Blake used for printing.
Millboard was made from waste paper, old tarred rope and/or pulp leftover from paper-making. The paper fibres were pressed together without added glue, and ‘milled’ smooth. Animal glue size could be applied later to make it less absorbent. It was easily cut to size.
The material would have been very suitable for Blake’s colour printing experiments. It was sold by artists’ colourmen, and was not expensive.
Several contemporary artists painted on millboard, as JMW Turner did here. This example is thin, and now too fragile to allow us to display of both sides at once. Blake would have used thicker board for printing.