Tammes P.M.L. (1964) Bird's egg shells, colour prints of nature. ARDEA 52 (1-2): 99-110

After a review of literature on the processes of pigmentation and the character of the pigments a comparison was made between the colours of the egg shells of various birds with the aid of the Ridgway Standards (1912). According to relevant literature the common pigments are biliverdine (blue) and protoporphyrin. Protophyrin may range from a red to a yellow colour in a scale of hues (Table 3). These colours occur both in the ground colour and the markings. It seems probable that porphyrins are not present on the eggs in a pure state but are combined as a prosthetic group with a protein (Volker 1942). Differences in the character of these simplexes may possibly be the cause of colour variations of protophyrin from red to yellow. When the porphyrin is split off by an invert soap and dissolved in chloroform one gets the same colour from either yellow or reddish brown eggs, with the characteristic red fluorescence in ultra violet light (Table 3). With red to yellow on one side and blue on the other, the three primary colours are represented and it is possible to obtain all colour manifestations as in a three colour print.