Make sure all dust and grit is brushed or washed from the glass. Do not rub it when dry. When clear of dust and grit, the surfaces may be cleaned using any soft cotton based cloth. Man-made fibres will eventually damage the surface. Dabbing the surface with a damp soapy cloth to remove dust and grit is safe. The glass can then be polished. Non-greasy window cleaning products used in conjunction with a cotton cloth should be safe, once all grit has been removed