Joseph Mallord William Turner

This watercolour on lightweight white wove Whatman was backed with two laminated sheets of a very similar white paper that is partially painted on the reverse and was probably an initial study. The main image has a graphite pencil drawing. Areas nearer the water, and some highlights in the foreground, were stopped out, before blue wash for the sky and then a brown wash for the foreground were applied very wet, to establish a colour harmony. The stopping-out for the foreground water prevented this wash 'taking' in this area if it ran over it: thus both stopping-out and initial laying-in could be done rapidly and spontaneously without the latter destroying the intention of the former. Quite a number of washes of mixed greens and mixed brown ochres followed, and the stopping-out survived it. This, and its slight fluorescence in ultraviolet light, suggests that Turner used glue size, possibly hardened with alum, to ensure that he could work over this area several times without losing the initial effect of the stopping-out. The pink wash, applied last, did 'take' as the stopping-out began to be washed off. This process is also sometimes called a resist technique.

The golden yellow pigment in the foreground is Indian yellow. This is fairly sensitive to light, but it has survived very well here, as have the pink and the mixed greens.

This composite work might have been intended to be viewed against a light, as a transparency. Related works are Chepstow Castle (Courtauld Institute of Art, London) and Llandeilo Bridge and Dynevor Castle (National Museum Wales, Cardiff) which appear to be more deliberately created as transparencies. The former has been painted carefully on the reverse so that the two images register and enhance the light/dark contrast when illuminated from behind.1 The latter is in effect a three-layer composite as is Norham Castle, but has a correspondingly registered image on the middle sheet, hidden from view until it is illuminated from the back, and only discovered in the course of recent conservation treatment.2 This construction suggests a more conscious preparation and presentation as a transparency than in the case of Norham Castle.