The fresco of the Pietà by Masolino da Panicale, painted around 1425 for the Baptistry of the Collegiata at Empoli, was detached from its supporting wall in 1946 and mounted onto a wooden reinforced wire using gypsum. Despite good climatic conditions, white-grey efflorescence soon occurred, that proved to be mainly sulfatic with some nitrate and microflora. Normal packings with ammonium-carbonate solutions in distilled water and paper pulp brought no stable results. Therefore a new transfer was started. After removal of the existing backing with its gypsum-layer and after a series of tests, five consecutive packings of a three centimeter-thick layer of Japanese tissue and Silica-Gel powder in distilled water were used, decreasing continuously the sulfate concentration to an analytically-controlled minimum. After drying, a new reinforced glass-fiber-support was provided and the surface was cleaned using the ammonium-carbonate process followed by its diffusion with barium-hydroxide. Besides removing sulfates, the now-green azurite-blue of the sky was transforming back to its original blue color. The reasons for the latter process are still under examination by the chemical laboratory of the Opificio delle Pietre Dure at Florence.