It looks like a typo for ceruse - lead white.

See http://naturalpigments.com/detail.asp?PRODUCT_ID=820-809: Rublev Colours Ceruse is a semi-opaque lead white and calcite ground in linseed and walnut oil like that used by Rembrandt and Velázquez. It is used for translucent white effects and soft tints when mixed with other colors.

Ceruse is made with lead white and a medium dry ground calcite (the calcium carbonate mineral) that has a low oil absorption rate like that of lead white to maintain the quick drying character of lead white. Calcite is semi-transparent in oil, giving ceruse its soft white character. In the 16th century, this mixture of lead white and calcite was favored as a mixing white by artists such as Rembrandt, and was known as lootwit in Dutch.

The name ceruse originates with the Latin cerüssa and currently refers to lead white (basic lead carbonate) pigment. In the 17th century, ceruse designated any white pigment made from tin or lead plates. Later, in the 19th century, the name ceruse was used for white pigments that contained lead and chalk.