This was painted on a very thick, high-quality artists’ hardwood panel which (unusually) lacks a suppliers label on the reverse. Turner used the panel as a sketching board, and could have accidentally soaked off any label as he worked. He glued down heavy paper along all four edges, painted on the restrained paper (which could be soaked with water, brushed and scratched vigorously, and left to dry before repeating these processes, or even dried near a fire indoors), and later loosened it with a knife, then tore it off roughly.
The board was used several times. When it was upright, the paper was a half-sheet of the larger sheet that had previously almost filled the board. Traces of watercolour paint in many colours, blobs of animal glue, and knife and tear marks in the remaining paper, form the evidence for this alternative use. No other Turner sketching board has survived…