The Chosen believe that at his Apotheosis a new God Emperor receives the 'essence' of the Twin Gods and that, in the process, his mortal blood is turned to pure ichor; the divine, the burning blood. Any child fathered by a God Emperor receives the gift of this ichor intermixed with the blood of its mother.
Deriving ultimately from a God Emperor, each of the Chosen carries a proportion of this ichor in his/her veins. The fraction of blood which is not ichor is called his/her Blood-Taint and is calculated in quyan fractions by the Wise and a record of it is kept in their Books of Blood. This blood-taint is inscribed along the edge of a blood-ring given to each of the Chosen at his/her coming of age. This ring is made of precious iron, whose smell and rust symbolize ichorous blood. Such rings can be used as seals.
Further, each of the Chosen has the blood-taints of his/her mother and father marked on their back with scarring combs. This marking is carried out by the Wise at the child's birth. The father's taint is put on the right side of the spine: the mother's on the left.
A child fathered by a God Emperor has its mother's taint placed on the right and the left is left unscarred to indicate the untainted blood of the father. This reversal is a result of the belief that a God Emperor is possessed of a sinistral nature associated with the darker aspects of the Gods.
A blood-rank is determined by the number of zeros in each of the subsequent positions in a blood-taint fraction. A zero in the first position is required if one of the Chosen is to be considered as belonging to the Great. Each zero corresponds to a blood-rank. One zero confers blood-rank one; two zeros blood-rank two and so on. A blood-rank of three is rarely found outside the House of the Masks - the God Emperor's own House. Blood-rank four is very high indeed and indicates a blood-taint with zeros in the twentieths, the four-hundredths, the eight-thousandths and the one hundred and sixty thousandths. The Empress Ykoriana is the first woman for generations with such august blood.