Viewing Topic "Lapis Lazuli"
There are two mechanisms by which natural (lapis lazuli) and synthetic ultramarine can fade or become gray: The first is caused by what is known as ultramarine sickness, which has been attributed to acid in the environment and paint film. The second cause occurs in oil paint. Due to the poor wetting of ultramarine pigment in oil, through hydrolysis the oil surroudning the pigment particles begin to degrade and cracks causing refraction which makes it appear as through the pigment is fading.
The previous post in this thread refers to lapis lazuli used in jewelry and not the pigment in paint.
Hi, low grade lapis are not grayish and niether it loses color from aging.
A fellow tempera painter recently told me that "Afghan lapis lazuli will grey out" with age. I understand that less well-washed grades of lapis have much less blue chroma and appear greyish from the start; and I've heard that acidic conditions can dull a genuine lapis lazuli to grey. But I haven't heard of a high grade lapis lazuli pigment turning grey merely from aging. Your thoughts?