||From the Journal of the Franklin Institute of the State of Pennsylvania, and Mechanics' Register.
Vol. 24, No. 3 (September 1839) pp. 202-204.
Observations on the application of Heliographic or Photogenic Drawing to Botanical Purposes; with an account of an economic mode of preparing the Paper: in a Letter to the Editor of the 'Magazine of Natural History.' By GOLDING BIRD, M.D., F.L.S., &c.
SIR,The mode of fixing the images of the camera obscura, and copying engravings, by means of the chemical action of light on paper prepared with an solution of chloride of silver, has attracted so much notice, and produced so much popular excitement, that a few observations on this interesting process will not perhaps be considered out of place in your Magazine. I venture to occupy your pages with the less reluctance, because I feel that the application of this heliographic or photogenic art will be of immense service to the botanist, by enabling him to procure beautiful outline drawings of many plants, with a degree of accuracy, which, otherwise, he could not hope to obtain.
That light will act on chloride of silver is by no means a novel discovery, and paper prepared with it was long ago used by Ritter and Wollaston in testing the chemical action of the rays of the solar spectrum; still, in this country it was not, I believe, applied to any purpose likely to be is use to the naturalist and traveller, until brought into notice by the researches of Mr Talbot. it is not a little amusing to observe how many pretenders in the discovery have started up since the announcement of Mr Talbot's discovery, and that of M. Daguerre in France. The latter gentleman has, through M. Arago, at a late meeting of the French Institute, announced his mode of preparing sensitive paper, far exceeding that of Mr Talbot in delicacy, but otherwise possessing the same property of indicating intensity of light by depth of colour, and consequently differing from that marvellous preparation which he is said to possess, and which represents shadows by depth of colour, precisely as in nature.
M.Daguerre prepares his heliographic paper by immersing a sheet of thin paper in hydrochloric ether, which has been kept sufficiently long to be acid; the paper is then carefully and completely dried, as this is stated to be essential to its proper preparation. The paper is next dipped into a solution of nitrate of silver (the degree of concentration of which is not mentioned,) and dried without artificial heat in a room from which every ray of light has been carefully excluded. By this process, it acquires a very remarkable facility in being blackened on a very slight exposure to light, even when the latter is by no means intense; indeed by the diffused day-light of early evening in the month of February. This prepared paper rapidly loses its extreme sensitiveness to light, and finally becomes not more readily acted upon by the solar beams than paper dipped in nitrate of silver only. M. Daguerre renders his drawings permanent by dipping them in water, so as to dissolve all the undecomposed salt of silver.
This process is very inconvenient, for many reasons, among which are the difficulty of procuring, as well as the expense of hydrochloric ether: on this account I prefer Mr. Talbot's process, although it is to be regretted that this gentleman has not stated more explicitly the proportions employed in the preparation of his sensitive paper. I have performed a set of experiments on this subject, and can recommend the following proportions as the most effective and economical. 200 grains of common salt are to be dissolved in a pint of water, and sheets of thin blue wove post paper saturated with the solution, which, for this purpose, should be poured into a dish, and, the paper being immersed, the application of the solution to every part should be ensured by the use of a sponge. The paper is then to be removed, drained of its superfluous moisture, and nearly dried by pressure between folds of linen or bibulous paper.
240 grains of fused nitrate of silver are then to be dissolved in twelve fluid ounces of water, and this solution is to be applied by means of a sponge to one side of each sheet of the previously prepared paper, which side should be marked with a pencil, so that when the paper is fit for use the prepared side may be distinguished. The sheets of paper are then to be hung upon lines in a dark room to dry, and when nearly free from moisture, their marked sides are to be once more sponged over with the solution of silver, and finally dried, they are then to be cut into pieces of convenient size and preserved from light, or even too much exposure to air, by being wrapped up in several folds of brown paper, and kept in a portfolio.
The proportions above recommended are sufficient for the preparation of a quire of the kind of paper alluded to; if more of the salt of silver were used, the paper would indeed become darker by the action of light, but its expense would be proportionally increased: and when prepared in the manner directed, it assumes, by less than a minute's exposure to the rays of the sun, a rich mulberry brown tint, of sufficient intensity to define outline very beautifully, which indeed is all that is required.
To use the paper, the specimen, of which a drawing is required, is removed from the herbarium, placed on a piece of the paper, and kept in situ by a pane of common glass pressed by weights: a piece of plate glass, however, is preferable, as it is sufficiently heavy to press the plant close to the paper. The whole is then placed in the sunshine, and in less than a minute all the uncovered parts of the paper will assume a rich brown tint. The paper should then be removed from the direct influence of the sun, and placed in a book until the drawing be rendered permanent: the specimen, quite uninjured by the process may then be replaced in the herbarium, and the drawing of another be taken, and so on. So rapidly is this process executed, that twenty-five or thirty drawings may be obtained in an hour, providing we are favoured with a direct sun-beam; if, however, we have only a diffused day-light, five or ten minutes, and sometimes even more, are required to produce a drawing with well-defined outlines.
If drawings of recent plants be required, specimens of proper size should be cut, and if not too rigid, placed on a piece of paper, and kept in a proper position by means of a pane of glass, as in the case of dried specimens; but if the plant be rigid, the specimens should be placed for twenty-four hours between folds of blotting paper, under a heavy weight before placing them on the sensitive paper.
Having obtained as many drawings as are required, the next thing is to fix them, so that their otherwise evanescent character may not deprive them of their value. For this purpose place them in a dish, and pour cold water over them; allow them to soak for ten minutes, and then transfer them to, or sponge them over with, a solution made by dissolving an ounce of common salt in half a pint of water, to which half a fluid ounce of tincture of sesqui-chloride of iron has been added. The drawings thus prepared may be dried by pressure between folds of linen, and exposure to the air; and may then be examined without danger. On looking at them, every one must be struck with the extreme accuracy with which every scale, nay, every projecting hair, is preserved ,on the paper; the character and habit of the plant is most beautifully delineated, and if the leaves be not too opake, the venation is most exquisitely represented; (this is particularly the case with the more delicate ferns, as Polypodium Dryopteris.) Among those classes of plants which appear to be more fitted than others for representation by this process, may be ranked the ferns, grasses, and umbelliferous plants; the photogenic drawings of the former are indeed of exquisite beauty.
The fact of the object being white on a brown ground does not affect the utility of this mode of making botanic drawings; indeed I most fancy that their character is better preserved by this contrast of tint, than by a coloured outline on a white ground. Every one will be fully aware of the value of this process to the botanist , in obtaining drawings of rare plants preserved in the herbaria of others, and which he would otherwise have probably no means of obtaining.
If the drawing of a tree or a large shrub be required, a box blackened inside, having a hole at one end about 1¼ inch in diameter, must be provided; in this hole should be placed a lens of 5 or 6 inches focus; if one of longer focus be used, the dispersion of light becomes too great to ensure an accurate representation. When the tree or shrub is well illuminated by the solar beams, the lens should be presented towards it, at a distance varying of course with the height of the object. A piece of card-board should then be placed in the box, a little beyond the true focus of the lens, and the former moved until a well-defined bright image of the tree, &c. is formed on the card, of course in an inverted direction. The box is then to be placed on any convenient support in this position, and a piece of the prepared paper fixed on the card, the lid of the box is then to be closed, and the whole left for half an hour, at the end of which time a beautifully accurate outline of the object will be found on the paper, which is then to be rendered permanent in the usual manner. It is obvious that this plan is unavailable on a windy day, on account of the branches of the tree, &c. being continually moving, so that it is of far less use to the botanist than the above described process for obtaining drawings of small specimens.
Various other applications of this paper will suggest themselves to the minds of naturalists.
(End of text. Please refer to our textnote regarding this text.)
Thanks to Richard Morris for the file, who also provides the following notes:
Golding Bird 1814-1834. Physician. Born in Downham Market, Norfolk, England. 1838 - took MD at St Andrews University. 1840 - MA. Licentiate of the College of Physicians, London. Lectured in medical botany. Married 1842 and left a widow and five children. He attended the British Association for the Advancement of Science Meeting in Liverpool 1837.
This article also appears in The Visitor or Monthly Instructor for 1839 (London: published by the Religious Tract Society)