Purcell has been working with the Wallace Collection in London for over 20 years, but the latest project to be completed is undisputedly the most radiant. Described as "the greatest picture gallery in Europe" by art historian Kenneth Clark, the Great Gallery runs the whole width of Hertford House. The gallery was last remodelled in the 1970s when air conditioning was introduced in the roof, blocking out natural light. The gallery's appearance was dated and worn looking and dominated by the large air grilles with artificial lighting. In order to re-introduce natural light and remove unsympathetic vents and grilles, the roof was re-configured within the retained external walls and its original iron structure was reused. Ventilation ductwork was designed to be compact and provided space centrally for a new lay light, set into an ornate fibrous plaster ceiling which also subtly conceals the environmental control grilles. Daylight is controlled by louvres and automatic blinds linked to the scene controller and low energy display lighting was installed. Pompeian red silk was applied to the walls, woven by Prelle of Lyon to a historically appropriate pattern.