'Grey Venice’ by Charles Napier Hemy Our photographer Keith Sweeney has taken these fascinating pictures as part of his behind-the-scenes work preparing for a new exhibition. He explains: "This painting, ‘Grey Venice’ by Charles Napier Hemy from the Walker Art Gallery’s collection, is one of many pictures of Venice from our collection that has been considered for inclusion in the upcoming Picturing Venice exhibition, which opens at the Lady Lever Art Gallery on 1 May. As part of the preparations for the exhibition I have photographed the paintings that might be included using different lighting techniques, so that our painting conservators can examine and condition check them. The first image shows the painting photographed in normal light in order to reproduce the painting as close to possible as the original. 'Grey Venice’ by Charles Napier Hemy photographed under raking light The second photograph has been taken using raking light (a bright light shone at a shallow angle across the surface), to reveal the surface texture of the painting. Conservators can use this technique to pick up a variety of surface features such as paint craquelure, uneven tension in a canvas, or warp in a panel. Raking light can even show individual brush strokes, which can sometimes reveal changes made by the artist during painting. The last photograph was taken using Ultra-Violet lighting (UV). I have to wear protective goggles when working with UV light to avoid damage to my eyes. UV light photography can reveal the presence of some natural resin varnishes and often evidence of previous treatment to a painting. Under UV light, varnishes can appear a pale milky green and dark spots will show if later areas of retouching are on top of the varnish." 'Grey Venice’ by Charles Napier Hemy photographed under UV light Senior Paintings Conservator David Crombie added: "These methods of technical photography are very valuable for establishing the condition of a painting, and identifying a number of possible problems. The raking light photograph of the Hemy shows a bulge in the top right corner – this can often develop if the canvas is torn at the edges. However, in this case, the edges were fine, and it seemed the bulge was an old distortion caused by a fault in the stretcher. As the canvas was not torn, the painting could be reframed. However this painting will not be included in the exhibition."