Rublev - "Crimson Ocher is a semi-transparent deep red with purplish-pink undertones, medium grained, low tinting strength and brushes "long" in the direction of the brush stroke.
The red earth comprising Crimson Ocher is a red iron oxide earth (red ocher) from quarries in Lori province of northern Armenia.
Red iron oxide or ferric oxide is the principle coloring agent in red ochers, such as Crimson Ocher. This color is based on the natural mineral hematite associated with varying proportions of other minerals such as clay, chalk and silica. They differ from other ochers in that they do not contain water bound with iron oxide. In other words, the iron to which they owe their color is iron oxide not hydrated iron oxide."
A beautifully transparent earth colour which given it's hue is geared towards portraiture however as it is a perfect 'glaze' it use is not limited to only this, imagine a glaze of this on the edges of clouds in a dramatic sunset painting.