A variety of tests were conducted to determine if the paint on the surface of the Archangel Michael is original to the sculpture and if it is authentic medieval paint. The tests concluded that both conditions were true. To test if the paint was original to the sculpture, scientists examined it using a microscope to see how and where the paint adhered to the stone, and tested the binding substance used to adhere the paint to the sculpture's surface. Under the microscope, the paint showed the proper structure for medieval pigments. They also found that the binding medium was casein, an adhesive substance derived from sour milk, which was used for its glue-like properties in medieval painting.
Next, the actual content of the pigments was tested. The blue paint was found to be azurite, which is derived from a copper ore and is not to be confused with that other famous and more expensive medieval blue - lapis lazuli. The red colour is provided by lead oxide, which was called minium in Latin, and was made by gently roasting white lead until it turned a reddish-orange.
Recently, further examination of the sculpture has observed a brown colour on the tunic, and a yellow/ochre colour on the robes. More investigation is needed to determine the authenticity and composition of these colours.
