NOV 17 1923 
U. 5"JfO 
[Reprinted from the Journal of Industrial and Engineering Chemistry, 
Vol. 14, No. 10, page 898. October, 1922 ] 
Iridescent Colors in Feathers' 
By Wilder D Bancroft 
Cornell University, Ithaca, N. Y. 
A T THE Rochester meeting I reported on the structural 
blues in feathers. That left the metallic or iridescent 
colors to be accounted for. Michelson 2 believes that 
the colors in the tail of the peacock and the throat of the 
humming bird are due to selective reflection, like the yellowish 
green metallic color of solid magenta. Lord Rayleigh 3 main¬ 
tains that the colors are the interference colors of thin films, 
often referred to as Newton’s rings. Since the question 
seemed to involve cooperative research by men representing 
different fields, the Heckscher Research Council made a grant 
to a committee consisting of Messrs. Bancroft, Chamot, and 
Merritt, representing physical chemistry, chemical microscopy, 
and physics. As an unofficial member representing ornithol¬ 
ogy, the committee has had the enthusiastic cooperation of 
Air. Louis Agassiz Fuertes, who was really responsible initially 
for the starting of the whole investigation. The work of the 
committee has been facilitated by the courtesy of Prof. A. A. 
Allen of Cornell University and of Dr. Frank M. Chapman 
of the Natural History Museum, who have supplied us with 
many typical feathers. For the experimental work the com¬ 
mittee has been fortunate in securing the assistance of Mr. 
Clyde W. Mason, assistant in chemical microscopy at Cornell 
University. It is to his skill and perseverance that the success¬ 
ful outcome of the investigation is due. 
While the nonmetallic blues are always in the barbs, the 
iridescent colors are wholly in the barbules, the barbs in such 
feathers being a dark dull brown and showing no color effects. 
The iridescent colors are visible by reflected light from both 
surfaces of the features but cannot be seen by transmitted light. 
By transmitted light the feathers of the blue jay, the tail feath¬ 
ers of the peacock and the throat feathers of the humming bird 
show no more signs of brilliant colors than do the feathers of a 
crow. 
There is not only no bright color to be seen by transmitted 
light in any metallic or iridescent feather, but no bright-colored 
pigment can be extracted by boiling with any organic liquid. 
If the dark or melanin pigment is extracted, the metallic color 
remains with little change until the dark pigment is practically 
all gone and can be detected even then when the feather is ex- 
i The investigation upon which this article is based was supported by 
a grant from the Heckscher Foundation for the Advancement of Research, 
established by August Heckscher at Cornell University. 
2 Phil. Mag., [6] 21 (1911), 554. 
> Ibid., [6] 37 (1919), 98. 
( 1 ) 
