Editing Ultramarine (section)

== Permanence ==
Easel paintings and [[illuminated manuscript]]s have revealed natural ultramarine in a perfect state of preservation even though the art may be several centuries old. In general, ultramarine is a permanent pigment. Although it is a [[sulfur]]-containing compound from which sulfur is readily emitted as H<sub>2</sub>S, historically, it has been mixed with [[lead white]] with no reported occurrences of the lead pigment blackening to become [[lead sulfide]].<ref name="Ashok-44-45" />

A plague known as "ultramarine sickness" has occasionally been observed among ultramarine oil paintings as a grayish or yellowish gray discoloration of the paint surface. This can occur with artificial ultramarine that is used industrially. The cause of this has been debated among experts, however, potential causes include atmospheric [[sulfur dioxide]] and [[moisture]], acidity of an oil- or oleo-resinous paint medium, or slow drying of the oil during which time water may have been absorbed, creating swelling, opacity of the medium, and therefore whitening of the paint film.<ref name="Ashok-44-45" />

Both natural and artificial ultramarine are stable to [[ammonia]] and caustic [[alkali]]s in ordinary conditions. Artificial ultramarine has been found to fade when in contact with lime when it is used to color concrete or plaster. These observations have led experts to speculate if the natural pigment's fading may be the result of contact with the lime plaster of [[fresco]] paintings.<ref name="Ashok-44-45" />