This painting presents a group of people in a reflected image. They stand in the low-beamed living-room of Belwethers, a cottage in the village of Cranleigh. The former country cottage of Mrs Halford, Lambert’s patron and friend, had been taken over by her daughter Mary and her son-in-law Sir Edmund Davis after her death in 1915. Sir Edmund stands at the window in the background; his wife, dressed in black, sits at the table; a maid serves tea; Amy Lambert, dressed in blue, stands; Sir Edmund’s sister-in-law Amy Halford sits with her hands on her lap; and the artist looks out of the image in the foreground. The oak beams in the ceiling take up half the picture and become, in the reflection, curved instead of straight lines, causing the design to flow in a circle – disturbing the very solidity of the room.

It is a jewel-like piece of painting, with the lustre of a looking-glass, in which Lambert explored the distinction between how things appear in the picture or in a mirror, or how they are in life itself. He placed the artist within the painting on a separate plane from the other people within the scene, and showed him ignoring them and looking out to the viewer – observing the entire scene through a convex mirror. His hand thrusts forward, without a brush, spread wide as it would when distorted in a mirror.

In 1916 Lambert visited Cranleigh, Surrey, when his son Constant became seriously ill with osteomyelitis while he was a scholarship pupil at Christ’s Hospital school in Horsham, West Sussex. (Cranleigh is situated halfway between Guildford and Horsham.) Constant’s condition was so grave that Lambert and Amy moved to Cranleigh to be near him. To pass the time, and determined not to give way to brooding over his sick son, Lambert painted The convex mirror , the reflection of a room in this cottage. Yet Lambert captured some of his sadness at the death of Mrs Halford (who acted as a grandmother to his children) and his anxiety over his son’s illness, as well as the universal unease and apprehension created by the First World War, in the way he presented the world through a convex mirror – disturbed and distorted.

Lambert carefully constructed the painting, drawing the lines of the beams and other structural elements onto the wood panel before commencing the painting. He used fine brushes to convey the scene. In addition to his masterful depiction of the illusion of a room viewed through a convex mirror, he also captured a soft light coming through the windows and lighting up the tablecloth and the cane chair.

Lambert saluted the sixteenth-century Italian mannerist painter Parmigianino’s illusionist tour-de-force, Self-portrait in a convex mirr or 1523–24 (Kunsthistorisches Museum, Vienna) in this painting. Like Parmigianino Lambert painted his work by looking at himself (and the others in the room) in a curved mirror and then recreating the effect. As in Parmigianino’s work, he captured the way the mirror widens the scene, enlarging everything nearby and making everything distant seem further away. But most significantly, like the Italian master, he created a display of virtuosity.

Many artists have included a convex mirror in their work, such as van Eyck in The Arnolfini portrait 1434 (National Gallery, London) in which the mirror probably reflects the painter himself; Quentin Massys in The moneylender and his wife 1514 (Musée du Louvre, Paris), which reflects the artist and the outer world into the picture; and Caravaggio in Martha and Mary Magdalene c.1598 (Detroit Institute of Arts, Michigan), in which the artist used the mirror to enable Martha to reproach Mary for her vanity.

The mirror device was fashionable at the  turn of the century, and frequently used by artists such as William Orpen. Orpen depicted himself reflected in a convex mirror on the wall behind his subjects in both  The mirror 1900 (Tate, London) and  A Bloomsbury family 1907 (Scottish National Gallery of Modern Art, Edinburgh) – a device Orpen borrowed from van Eyck’s TheArnolfini portrait , which he would have known in the National Gallery. Likewise, genteel interiors, universes of the private individual, were popular subjects during this period, particularly in the exhibitions of the New English Art Club. In this work, Lambert depicted mistresses and maids, and the daily domestic ritual of tea. He depicted people reading and reflecting in the comfort of familiar surroundings. He also showed the master looking out the window and the wider world beyond. And he presented sun coming through the windows and lighting up the interior.

Thea Proctor wrote in The Home on 1 July 1930 that The convex mirror ‘has the exquisite finish of the Dutch Masters, and shows that a present-day artist could also paint small things in a large manner’.