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Some others have included chevron shaped compositions (which are simply square canvases that hang from one corner) like Leaving harbour, Newlyn, multiple chevrons (Kanorian Enev at Morvah) and triangular pieces (Stream flowing to the sea, Cot Valley). These were just some examples. In fact Tom had been experimenting with a wide variety of different formats since his student days in Italy when the altarpieces and sections of fresco decoration he came across in museums, churches and monasteries inspired him in that direction. The shape of the painting surface became an important part of the idea behind each of his pictures.
In every case there was a good reason for his choice of shape. Whether it was one of the more unusual ones mentioned above or whether he chose to use a less unusual vertical or horizontal rectangle of particular dimensions, the choice will have arisen from something in the visual encounter that led to the impetus to create the piece.
In the case of the Cornish tree on the slopes of Tregeseal Valley the reason for the trapezoid shape arose from a wish to emphasise the way the tree had developed at this strange angle due to the saltiness of the wind from the sea. Tom also wanted to set this against the long diagonals of the hedges and valley shapes from lower left to upper right while keeping the contrasting lines of buildings and some of the distant field boundaries more abrupt for contrast.