The Restoration of The Mystic Marriage of Saint Catherine, c. 1500
On November 1st, 1500 a new cappellania or chaplaincy was founded on the altar of Saint Catherine by the priest Alberto di Michele di Antonio in the small chapel of San Jacopo at the center of Florence. The following year a panel painting il Matrimonio Mistico di Santa Caterina di Alessandria was commissioned to decorated the altar. At the center of the painting the Virgin Mary is richly dressed and holds the infant Christ in her lap.
Overcleaning
Small separations in the gesso ground, indicate that an over cleaning took place using caustic methods. Caustic alkalis, soaps and abrasives were common method of cleaning during the sixteenth century through to the eighteen century. As a result, the ground layer has literally been eaten into and opened up forming little “cracks” in the pictorial surface. Areas have been opened up all the way down to the preparatory under drawing
Azurite
Mineral pigments such as azurite would lose their color and appear grey if ground down too small a particle size, explaining the rough, course surface of the paint. Because it is a copper based pigment, similar in molecular makeup to that of malachite, azurite will begin to turn a greenish-blue due to the reaction of copper with sulfur in the air. Due to its large granules, azurite tends to absorb more of the oils and varnish, giving it a yellowish ting.
Verdigris
Verdigris was a very unreliable pigment as it tended to react chemically and darken when mixed with sulphide-based pigments or with sulfur that is present in the air. In the presence of light and air, green copper resinate becomes a brown copper oxide. At times, copper resinate is rather transparent and was often used as an over paint to increase the depth of saturation of an opaque green. However, vergidris is also quite poisonous and fell out of use by artists as more stable green pigments became available.
False Glue Patina
The most challenging part of cleaning this panel painting was trying to retain a layer of the false glue patina which tends to ball up in areas or becomes uneven very quickly. It is difficult to predict how the patina will react in certain areas so at times it can be a slow process of working from areas to area. However to do a careful, proper job of cleaning and restoring any painting, particularly one that is fragile or damaged it take time; sometimes months or even years to complete. The restoration of The Mystic Marriage of Saint Catherine was begun in February of 2009 and due to the size as well as the extensive damage wasn't completed until 2012.
