If the original be a plant, a flower, or an insect, a texture, or in short, any lifeless object whatever, it is passed between a copper plate and a lead plate, through two rollers that are closely screwed together. The original, by means of the pressure, leaves its image impressed with all its peculiar delicacies -- with its whole surface, as it were -- on the lead plate. If the colors are applied to this stamped lead plate, as in printing a copper plate, a copy in the most varying colors, bearing a striking resemblance to the original, is obtained by means of one single impression of each plate. If a great number of copies are required -- which the lead form, on account of its softness, is not capable of furnishing -- it is stereotyped, in case of being printed at a typographical press; or galvanized, in case of being worked at a copper-plate press, as many times as necessary; and the impressions are taken from the stereotyped or galvanised plate instead of from the lead plate. When a copy of a unique object, which cannot be subjected to pressure, is to be made, the original must be covered with dissolved gutta percha; which form of gutta percha, when removed from the original, is covered with a solution of silver, to render it available for a matrix for galvanic multiplication.
This process is also applicable to the purpose of obtaining impressions of fossils, or of the structure of an agate or other stone. In all the varieties of agate, the various layers have different degrees of hardness. Therefore, if we take a section of an agate and expose it to the action of hydro-fluoric acid, some parts are corroded and others not. If ink is at once applied, very beautiful impressions can be at once obtained; but for printing any number, electrotype copies are obtained. These will have exactly the character of an etched plate and are printed from in the ordinary manner. The silicious portions of fossil, and the stone in which they are imbedded, may in like manner be acted upon by acid, and from these, either stereotyped or electrotyped copies are obtained for printing from.
_Dresser's Process of Nature Printing._
The process is one by which images of foliage may be taken by any who have leisure and choose to devote an hour or two to the registration of the beautiful forms of our leaves. The process, by its simplicity, commends itself; and the results gained are of the most charming character. The Vienna process of nature printing has achieved much, and produced results of the most admirable character, but the process necessitates the use of dried vegetable specimens, in order to the production of the image. While this is at least no drawback in the case of ferns, and is perhaps even an advantage, yet it strongly militates against the process in the case of many other plants. In order to meet this difficulty, Dr. Dresser suggested an "Improved Nature Printing" process which he patented, in conjunction with Dr. Lyon Playfair, in which impressions are taken from the living plant, and which may be substantially described as follows: A sheet of foolscap writing-paper should be provided, a handful of fine cotton-wool, a piece of muslin, one or more tubs of common oil-paint (according to the color required), a little sweet-oil, and a quantity of smooth, soft, cartridge-paper, or better, plate-paper. Having placed the sheet of foolscap paper while doubled (the two thicknesses making it a little softer), on a smooth table, squeeze from the tube about as much oil-color as would cover a shilling, and place this on one corner of the sheet of foolscap; now form a "dabber" by enclosing a quantity of the cotton-wool in two thicknesses of muslin, and tying it up so as to give it roundness of form. Take up a portion of the oil-paint from the corner of the paper, with the dabber, and by dabbing give the central portion of the sheet of foolscap a coat of color. This dabbing may be continued for half an hour or more with advantage, taking a small quantity more color when the paper becomes dry; two or three drops of sweet oil may now be added to the paper and distributed by the aid of the dabber, if the color is thick, when the paper will be fully prepared for use.
The paper may be left for an hour or two after being first coated with color without injury, and, indeed, this delay is favorable, for until the paper becomes impregnated with oil, the results desired are not so favorable as they become after the paper is more fully enriched with this material. While the color is soaking into the paper, a number of leaves should he gathered which are perfect in form and free from dust, and these can be kept fresh by placing them in an earthenware pan, the bottom of which is covered with a damp cloth, but it will be well to place a damp cloth over the orifice of the pan also. Selecting a woolly, hairy leaf, place it on the painted portion of the sheet of foolscap, and dab it with the drabber till it acquires the color of the paint used; this being done turn the leaf over and dab the other side; now lift it from the paint paper by the stalk, and place it with care between a folded portion of the "plate" or "cartridge" paper, and if the stalk of the leaf appears to be in the way, cut it off with a pair of scissors; now bring down the upper portion of the folded piece of paper upon the leaf, and rub the paper externally with the finger, or a soft rag, bringing the paper thus in contact with every portion of the leaf. If the paper is now opened, and the leaf removed, a beautiful impression of both sides of the leaf will be found remaining. In like manner, impressions of any tolerably flat leaves can be taken; but harsh leaves will be found most difficult, and should hence be avoided by the beginner. While the paper is yet rich in color, downy leaves should be chosen; but color may at any moment be added, care being always taken to distribute the paint evenly over the paper with the dabber before the latter is applied to the leaf, and the dabber is always removed from the painted paper till the color is exhausted, when the paper is again replenished from the reserve in the corner.
As the color on the paper becomes less and less in quantity, smoother leaves may be employed; and when the paper seems to be almost wholly without paint, the smoothest leaves will prove successful, for these require extremely little color. Should the natural color of the leaf be desired, it can be got by using paint of the color required; but, in many cases, purely artificial tints produce the most pleasing and artistic results; thus, burnt sienna gives a very pleasing red tint, and of all colors this will be found to work with the greatest ease.
By the process now described, the most beautiful results can be gained, but the effect will be better, if, when the impression is being rubbed off, the leaf, together with the paper in which it is enclosed, is placed on something soft, as half a quire of blotting paper. Should the first attempt not prove very satisfactory, a little experience will be found to be all that is required, and now the most common leaf will be seen to have a form of the most lovely character.
Collections of leaves of forest-trees will prove of the deepest interest, or of all the species which we have of any kind of plant; thus, if the leaves of the black, red, American, and golden currant be printed together with that of the gooseberry, all of which belong to one botanical genus or group, the variation or modification of the form will be seen to be of the deepest interest.
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