The three year restoration project of stained glass windows from Chartres began in 1976. Three were cleaned with water and a wetting agent, then varnished with Viacryl, a synthetic polyurethane resin. The resin, it was argued when the windows were replaced, destroyed the gloss and color balance, their patina and the way they transmit light. Some critics thought the resin could not be removed with a known solvent, and that it was permeable to moisture and sulfur dioxide. Restorers said Viacryl can be removed, with Cital 1212. They argued that color balance after cleaning had changed due to the greater accumulation of dirt by the warmer tones. Blues, having less potassium which reacts with water to form darkening sulfates, change less. See also 18-507. -- AATA