In 1987, Gillian Ayres left Wales and went to live at Tall Trees in a coastal valley on the Devon-Cornwall border. The area is characterised by lush greenery and dramatic vistas, and was designated in 1959 as the North Devon Area of Outstanding Natural Beauty. It was at Tall Trees that Ayres made Choo Choo in 1996. The title of the painting perhaps refers to the whistle of a steam engine, and a steam line – the Lynton & Barnstaple Railway – passes through the valley. Her titles were never literal, however, and were always ascribed some months after a painting was completed, as she explained in 2000.
I like the titles to be strong because it helps me to remember the paintings; it identifies them. It has to be something I like [...] then it sort of strangely has to suit the painting. [...] But it's certainly not what the painting is about.
Though Ayres made abstract paintings all through her career, her work went through many different iterations of non-representation, beginning in the late 1950s with a style of action painting derived from the brush-free techniques of Jackson Pollock. From the late 1970s until the end of her life in 2018, she developed a consistent approach using thickly applied impasto, bright contrasting colours, and clearly defined painterly forms. These works were executed without preliminary designs. In Choo Choo, the brushwork is spontaneous and freely accumulated, the final surface being built up gradually as the artist worked towards an image that was internally complete and visually satisfying.
The rare, defining quality of Ayres’s abstract painting is the bright and crisp quality of the paintwork. Every brushstroke was richly loaded with paint, posing the technical challenge of how to maintain clearly defined shapes and the integrity of each application of the brush. When using paint so thickly, the surface might easily become mired as colours start to bleed into one another. Writing in 1987, the curator Susan Compton summed up the technical achievement of Ayres’s painterly style. ‘By the time she painted Lure  her love of colour and expansive methods of working had spilled out on the canvas: the juxtapositions of colours – which never become muddy – anticipate the freedom with which she has developed the use of brilliant pigments in the thickly painted canvases of her maturity.’ Ayres achieved this clarity by working on several paintings at a time, allowing her to resume work on other pieces while fresh applications of paint dried out. Drying time allowed the surface to solidify, the artist to contemplate her next steps in the painting, and then for new, heavy-laden brushstrokes to overwrite and juxtapose the pre-existing surface.
In the final stage of Ayres’s stylistic development, from the late 1970s until her death, the tenor of abstraction began to reveal an underlying, unintentional response to her surroundings. Though the outcome is always non-representational, titles like A Midsummer Night (1990, Birmingham Museums) suggest an external inspiration for the work. Speaking to Mel Gooding in 2000, Ayres said ‘I don’t know how these things enter my work… they can put you on a high perhaps. […] I don’t mind if things get into me.’ Though she was reticent to explain how her surroundings affected her paintings, a loose connection evidently existed between the two things.
Ayres consciously sought to identify visual clichés and avoid them. She regarded the horizon line in art as a cliché, for instance, which accounts for the roughly geometric tabulation used in Choo Choo which divides the painting into quadrants defined by a grid of pastel green lines. Several of the resulting quadrants are predominated by circle motifs – a central area of colour ringed by another, contrasting colour, occasionally with an additional roundel or a halo of dots. The circle motif is a defining feature of her work from the 1990s, appearing some years before Choo Choo in a work like Say the Bells of St Clement’s (1991, London Transport Museum).