Relief carving of a rotary anhydrite kiln and sulphuric acid unit, made from a piece of anhydrite, by Ophelia Gordon Bell. The plaque was formerly displayed in the entrance hall of the United Sulphuric Acid Corporation (USAC) offices at their Green Oaks Works. The plaque also includes the names of member companies of USAC. It is now in the café at Catalyst Science Discovery Centre, Widnes, England.