Varnishing days were introduced at the Royal Academy in 1809, being three to five days during which artists could come in and apply a final coat of varnish or touch up their paintings before the exhibition.

Turner is said to have deliberately brought in unfinished canvases so that he could show off his technique on them. He made a point of not stepping back to look at the effect, but when finished he would ostentatiously go off sideways without looking at them. It may be that he was inspired after seeing Paganini and wanted to give a similar display of his own virtuosity.

Many of these incomplete Turners are now in the Clore Gallery at Tate Britain in London, and they are quite extraordinarily abstract: they would have been incomprehensible in his own day.

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