A PHOTOGRAPH IN NATURAL COLOURS. 
45 
Photographs in natural colours, produced by the late M. 
Niepce de St. Victor, were recently exhibited at a meeting of 
the London Photographic Society. Having repeated M. Bec- 
querel’s experiments, already described, M. Niepce conceived 
that it was possible there might be some relation between the 
colour which a body communicated to a flame, and the colour 
which light developes on a plate of silver that had been chlori- 
dised with the body that coloured that flame. The bath in 
which he immersed the plate was formed of water saturated with 
chlorine, to which he added a chloride endowed with the pro- 
perty of imparting to flame the colour he wished reproduced on 
the plate. Strontium, for example, caused the red and purple 
tints to be vividly impressed ; to excite the orange ray, 
calcium or uranium was used ; sodium or copper sufficed for 
the yellows, and so forth. Pictures possessing a fair degree of 
brilliancy in their colours may be obtained in this way. 
An important advance in heliochromy has been made by 
M. Poitevin, who, instead of using metallic plates, has employed 
paper as the groundwork of his experiments. Starting on the 
basis of Herschel’s original discovery, he takes paper and pre- 
pares it with subchloride of silver. The method of doing this 
is known to every intelligent photographer, consisting in expos- 
ing to light ordinary chloride of silver, whether spread upon 
paper by the usual washes, or formed in collodion, as suggested 
by the late R. J. Fowler, the advantage of the latter being that 
it opens an avenue for reproductions — a la negative — from the 
picture first obtained. Confining our description to the pro- 
duction of heliochromes upon paper, with which we have con- 
ducted numerous successful experiments, we observe that the 
problem which presented itself was the production of a sub- 
chlorised paper and of an oxidising agent which, when exposed 
to the coloured rays, should reproduce those colours with the 
greatest possible degree of brilliance, and in the shortest pos- 
sible period of time. How far these conditions have been 
fulfilled will presently be seen. A piece' of subchlorised paper 
was floated for a minute on a saturated solution of bichromate 
of potash, a twenty-grain solution of chloride of potassium, 
and a saturated solution of sulphate of copper mixed together 
in equal volumes, and was then hung up to dry in a dark 
room ; after this it was ready for exposure. The record of one 
trial will afford an opportunity of judging how far success was 
achieved. Some brilliantly-painted magic lantern slides were 
obtained, and under these were placed pieces of the sensitive 
paper, the whole being then exposed to the light of a cloudy 
sky. After an exposure of fifteen minutes, one of the pictures 
was taken into a darkened room and examined. The subject 
was an Arab with a red garment, the sky being blue, and the 
