A Manual Of Photography

THE COLOURING MATTER OP ELOWERS. 65 clean linen or cotton cloth. It was then spread on paper with a flat brush, and dried in the air without artificial heat, or at most with the gentle warmth which rises in the ascending cur- rent of air from an Arnott stove. If alcohol be not added, the application on paper must be performed immediately, since exposure to the air of the juices of most flowers (in some cases even but for a few minutes) irrecoverably changes or destroys their colour. If alcohol be present, this change does not usually take place, or is much retarded; for which reason, as well as on account of certain facilities afforded by its admixture in pro- curing an even tint (to be presently stated), this addition was commonly, but not always, made. “Most flowers give out their colouring matter readily enough, either to alcohol or water. Some, however, as the Escholzias and Calceolarias, refuse to do so, and require the addition of alkalies, others of acids, Ac. When alcohol is added, it should, however, be observed that the tint is often apparently much enfeebled, or even discharged altogether, and that the tincture, when spread on paper, does not reappear of its blue intensity till after complete drying. The temporary destruction of the colour of the blue heartsease by alcohol is curious, nor is it by any means a singular instance. In some, but in very few cases, it is destroyed, so as neither to reappear on drying, nor to be ca- pable of revival by any means tried. And in all cases long keep- ing deteriorates the colours and alters the qualities of the alcoholic tinctures themselves ; so that they should always be used as fresh as possible. “ If papers tinged with vegetable colours are intended to be preserved, they must be kept perfectly dry and in darkness. A close tin vessel, the air of which is dried by quicklime (care- fully enclosed in double paper bags, well pasted at the edges to prevent the dust escaping), is useful for this purpose. Moisture (as already mentioned, especially assisted by heat) destroys them for the most part rapidly, though some (as the colour of the Senecio splendens) resist obstinately. Their destructibility by this agency, however, seems to bear no distinct relation to their photographic properties. “This is also the place to observe that the colour of a flower is by no means always, or usually, that which its expressed juice imparts to white paper. In many cases the tints so imparted have no resemblance to the original hue. Thus, to give only a few instances, the red damask rose of that intense variety of colour commonly called by florists the black rose, gives a dark slate blue, as do also the clove carnation and the black holly- hock : a fine dark brown variety of sparaxis gave a dull olive E