Bolus (pigment)
Bolus is an earth pigment that occurs naturally in different colors : it can be white , yellow , red or gray . Such earth pigments are made up of clay , alumina and water-containing aluminum silicates .
Types of paint
The red bolus ( Bolus Rubra ) was mostly imported from Armenia and was therefore given the name Bolus Armenicus , Bolus Armena, Lutum Armenum, Terra Armenum etc. The coloring component is iron oxide (red ocher , Fe 2 O 3 ), which contains up to 20% can be. In addition, it mainly contains clay minerals .
The yellowish-red bolus ( Bolus Luteus ) was promoted on the Levant . The yellowish color is caused by the proportion of iron oxide hydroxide (yellow ocher , Fe O [OH]).
The white bolus ( Bolus Alba , Kaolin ) is mined in Moravia and Norway . The color tone is determined by magnesium oxide ( Mg O ).
use
Bolus was used under the name Poliment , especially in panel painting for gold grounds . For this purpose, prepared, purified bolus was used, which was mixed with a binding agent such as animal glue or egg white . The gold leaf or another metal leaf was then placed on top of this.
See also
Individual evidence
- ↑ Poliment gold plating ( Memento from July 11, 2012 in the web archive archive.today )
- ↑ Ferd. Ludw Strumpf: Systematic Handbook of Drug Science, Volume 1 . 1848 ( page 369 in the Google book search).
- ↑ Katharina Möhring: The pulpit altar of the church in Selbelang. Berlin, September 2000, page 66, footnote 170, online ( memento of October 6, 2007 in the Internet Archive ) (PDF).