« PreviousContinue »
aqua fortis, of those made by the intervention of that liquid the principal is Etching, he that would excel in this branch of the arts must be thoroughly acquainted with drawing, otherwise his works will appear tasteless indeed. The ground used in etching is a combination of asphaltum, gummastick, and virgin wax, mixed in such proportions as will prevent the asphaltum from breaking the composition when under the aqua fortis, or the wax from making it so soft as to close the lines when cut through it by the needle. As every thing depends upon the stability of the ground, it should be purchased of those persons who are most celebrated for making it; or if the person wishing to use it prefers doing it himself, let him remember that he must keep every particle of grease or oil far from him and his materials, and that without the greatest care the inflammability of the asphaltum will ruin his operations in melting them. The proportions of the ingredients should be obtained by experiment.
After being prepared in the above manner the ground is tied in a piece of lustring for use, and another piece of the same kind of silk must be made into a dabber by tying a quantity of cotton in it. The copper-plate, hammered to a considerable degree of hardness, polished as if intended for the graver, and perfectly cleansed with whiting, is then secured at one corner by a hand vice, heated over a charcoal fire, and the silk containing the ground rubbed over it till every part is covered by the melted composition; but before it cools the silk dabber must be applied in all directions, till the surface of the plate is thinly and equally varnished. After this part of the process is completed, several lengths of wax taper, twisted together, are to be lighted, the plate raised by the vice in the left hand, and the right holding the burning taper is to be moved gently backwards and forwards under the ground, carefully avoiding touching it with the wick, yet causing the flame to spread over the surface, which will render it perfectly black, smooth, and shining, in a short time; this is to be ascertained by turning the plate: if the copper appears through the ground, the taper must be applied again immediately; but if it is held too long beneath the plate, the ground will become opaque, and break when the aqua fortis is used.
The next object is to transfer the design to the ground, which may be done by drawing it on thin white paper with a black lead pencil, and having it passed through
the copper-plate printers' rolling press, who will accomplish it by laying the plate carefully on the board of his press, the pencilled paper slightly damped on it, and turning the press the lead will be conveyed firmly to the ground, which will appear in perfect outlines on removing the paper. Another method is to draw the design reversed from the original; rub the back with powdered white chalk, and laying it on the ground trace the lines through with a blunt point; this operation requires much precaution or the point will cut the ground; besides, if the paper is not securely fastened with wax at the corners it may slip, and either interrupt the true continuation of lines, or scratch the ground.
In working with the etching needle nothing more is required than to keep it upright, that the lines made by it through the ground may not slope, and thus make the aqua fortis corrode improperly; but it should be particularly observed, that the point, though taper, must be so rounded as to be free from a possibility of its tearing the surface of the copper, which would prevent the progress of the point, and ruin the plate when bitten; the necessary polish of the point may be accomplished by rubbing it on the sole of a shoe. The young artist must now be left to his own exertions, as directions for etching beyond those already given are useless, and he will acquire more knowledge and freedom from copying good prints in one week than a quarto volume of observations would afford. It seems almost needless to add, that every line must be kept distinct, at all events, throughout the plate, and that the most distant should be closer and more regular than those in the fore ground, as the greater the depth of shade the broader and deeper must the lines be made.
When the etching of the plate is completely finished, the edges of it must he surrounded by a high border of wax, so well secured that water will not penetrate between the plate and it. The best spirits of nitre fortis must then be diluted with' water, in the proportion of one part of the former to four of the latter, which will be found to answer the first operations, if the weather is fine and the atmosphere free from moisture; but, if the contrary is the case, the spirits of nitre must be increased in proportion to the humidity of the air; this, when poured on the plate, cannot be too attentively observed in order to remove the bubbles of fixed air with a feather, and to ascertain the time for
•topping out the lightest parts; for it must be remembered the whole secret of biting or corroding any subject consists in the judicious manner in which the depth and breadth of the lines are varied, as by proper management they may be left scarcely perceptible, or increased very considerably. The composition used for the above purpose is, turpentine varnish mixed with lamp-black, and diluted so as to he used freely with a camel's hair pencil; this applied to the parts of the plate sufficiently corroded, will effectually prevent the aqua fortis from touching it again, and the remainder proceeds as if no such application had taken place: it will be necessary to strengthen the water as the work becomes nearer completion, but cautiously, lest the ground should be broken; and every time the aqua fortis is removed the plate must be washed with clean water and gradually dried, otherwise the varnish cannot be used, and the lines would be clogged with the decomposed metal. For taking the ground from the plate it is usual to cover the surface with olive oil, and heating it, wipe the plate with a soft piece of old linen and spirits of turpentine, will effectually remove all remaining dirt.
Re biting, is the art of strengthening those lines of an etching in a plate from which the original ground has been cleansed. This is done by applying the ground as at first directed, but with great care that the melted composition does not fill, or even partially fill the lines, to prevent which the cotton wrapt in silk, called the dabber, should be used exclusively by taking a small quantity of melted ground on it, and gently touching the parts between the lines till they are equally and completely covered; if the plate is considerably heated, the ground will spread with more facility over the various interrupted surfaces. Carelessness or inattention will instantly ruin this process, and the whole of the plate: a border of wax must surround the parts to be rebitten, and a channel made to carry off the aqua fortis without injuring those already completed. Supposing the operations of etching and biting the plate entirely finished, nothing more remains than to examine it attentively, and improve it with the graver and dry point.
Slipling, or engraving in the dotted manmer, was in a great measure introduced by Bartolozzi, whose works in this way are astonishingly numerous, rxrhuive of those to which hu name is affixed and not the products of himself. Some pastoral scenes,
with figures, when printed in colours have a pleasing effect; and small portraits stipled will bear examination; but historical subjects, which have great breadth of shade, appear to no advantage engraved in this manner. Stipling is performed by etching the plate with dots and biting it, laying the shades with a tool for the purpose, using the graver and the dry point, and scraping off the roughness thus occasioned.
Engraving in Aquatinta. The print from an aqua-tinted plate resembles a neatly finished drawing in Indian ink; this effect is produced by corroding the plate between the particles of a material entirely different from the etching ground. The first step in this process is to prepare a plate exactly in the way already described, and etch the outlines of the subject to be aqua-tinted, which are to be slightly bitten, and the plate thoroughly cleansed. The substance used to form the grains of the subject (which may be common resin, burgundy-pitch, asphalt- tum, gum-mastich, or gum-copal, either separate or mixed) should be reduced to a fine powder and sifted, put into a piece of muslin, and holding it high above the plate it must be struck against any substance held in the left band till the shower of dust thus produced has covered the plate equally throughout, preserving it carefully in this situation, the plate is to be heated sufficiently to melt the powder, which will make the grains assume a circular form, and contract, leaving, when cold, a beautiful surface fit for the aqua fortis. Common resin is generally preferred for this part of the operation, but gum-copal is less liable to be broken loose from the plate during the process of biting.
The drawing to be copied must serve as the future basis of proceeding, which is to be imitated in the following manner: the perfectly white parts of the intended print are to be covered on the plate, with the varnish mentioned in etching, by the use of a camel's-hair pencil; a border of wax must then be raised, and the aqua fortis diluted poured on; the same method is afterwards practised in the stopping out before recommended, except that the depth of the corroding cannot be so great as in the line manner.
In order to obviate any difficulties which occur in procuring sufficient depths of shade, a method has been invented that enables the artist to produce an effect almost equal to the decisive touches of a brush filled with colour in drawing, which is the use of a liquid made with water, treacle, M sugar, and fine washed whiting, exactly of the consistence of Indian ink, and laid on the granulated surface with a pencil, in the same free manner adopted on paper; after the above composition is thoroughly dry, the whole plate must be covered with a thin, weak, varnish of mastich, turpentine, orasphaltum, and when dried a second time, the aqua fortis is to be applied, which immediately breaking the varnish and whiting, will corrode the plate precisely in the marks of the pencil. The border of wax may be removed by heating the plate gently, and the ground varnish, &c. by oil of turpentine; a little fine whiting and a clean rag will then render the plate fit for the printer.
As the manner of procuring the grain by beating the powdered substance scattered over the plate is liable to objections, on account of the difficulty of making the particles assume the desired coarseness, or the reverse, and the engraving so produced rapidly wearing out in the printing, another has been contrived far more certain and satisfactory. In this mode, common resin, mastich, or Burgundy pitch, is dissolved in highly rectified spirits of wine of the best quality, each of which produce different descriptions of grains; but these substances may be mixed in such proportions as the artist prefers, and he must recollect that the resin makes the coarsest: to satisfy himself in this particular, the grain of every proportion should be tried on useless pieces of copper. Having a solution to his mind, it must remain undisturbed till every impure particle has subsided. The plate, polished and cleansed with whiting, is then placed to receive the liquid, which being poured on it, is held slanting till the most fluid parts has run off; it is afterwards laid to dry, in the progress of which the resin granulates, and adheres firmly to the surface. The greatest precaution must be used in going through this process, as the interposition of dust, grease, hairs, or fibres of linen, will cause total derangement, and even then it is subject to most vexatious uncertainty, often compelling the experienced artist to renew it to obtain a good grain; in short, the weather and untoward accidents frequently ruin his labours, though guarded against by every method his invention suggests. There is one advantage attending the pouring the liquid off, which is, that the heaviest particles of the resin will float to the lower side, and consequently leave a coarser grain there than above, much better suited to the deep shades of a
landscape than if the granulations had been equally fine; in large subjects the grain is sometimes laid coarse purposely in the parts requiring it.
Although a fine grain has a very pleasing effect, and will bear close examination, it has several disadvantages; for this reason a medium description of granulation is preferable, which admitting the aqua fortis freely to the copper, it bites deeper, and is less apt by acting laterally to force off the resin, besides, the plate will of course afford a greater number of impressions.
Some hints have been given already for biting the plate; but however nsefnl those may be found in particular instances, there are others which can only be extracted from close application and experiment, and those are often varied in their results: as an illustration, we may suppose an artist provided with several pieces of copper granulated, and trying each successively by his watch with spirits of nitre diluted to the state of the air at the commencement of his operations, how many minutes is necessary to produce one tint, how many for a second, &c, granting him two hours for his experiment; during this interval a violent shower of rain may occur, which will immediately affect the acid by weakening its properties in the same proportion as salt is observed to be dissolved by a humid atmosphere: thus it appears, a result obtained on a clear dry day will not suit a rainy one, and tsice versa.
In opposition to this discoursing uncertainty, and in opposition to the judgment and preference of all true connoisseurs, aquatinted prints seem to increase in value in the estimation of many persons, who forget that national taste should be improved by works of superior execution, and not vitiated by being constantly familiarized to those produced by means which set genius at defiance.
ENNEAGON, in geometry, a polygon with nine sides. If each side be 1, the area will be 6, 18, &c.
ENNEANDRIA, the name of the ninth class in Linnaeus's sexual system, consisting of plants which have hermaphrodite flowers, with nine stamina or male organs. The orders, or secondary divisions, in this class are three, being founded on the number of the styles, seed buds, or female or gans. Lauras, tinus, and cassytha, have one style; rhubarb (rheum), has a triple stigma or summit, but scarce any style; flowering rush has six styles. The genera just enumerated are all that belong to the class Enneandria. Tlic first genus, laurus, is very extensive; comprehending the baytree, cinnamon tree, camphor tree, benjamin tree, sassafras tree, and the avocado or avocado pear.
ENS mar/us, an old name given by chemists to sal ammoniac sublimed with iron filings, and therefore consisting of muriate of ammonia mixed with a little muriate of iron.
Ens veneris, a similar preparation, in which coppertilings are substituted for those of iron.
Ensatje, (from enses, a sword), the name of the sixth order in Limraus's Fragments of a Natural Method, consisting of plants with sword-shaped leaves.
ENSIFORM, in general, something resembling a sword, emu: thus we find mention of ensiform leaves, ensiform cartilage, &c.
ENSIGN, in the military art, a banner under which the soldiers are ranged according to the different companies or parties they belong to. The European ensigns are pieces of taffety with various figures, arms, and devices painted on them in different colours: the Turkish ensigns are horses' tails.
Ensign is also the officer that carries the colours, being the lowest commissioned officer in a company of foot, subordinate to the captain and lieutenant. It is a very honourable and proper post for a young gentleman at his first coming into the army ; he is to carry the colours both in assault, day of battle, &c, and should not quit them but with his life; he is always to carry them himself on his left shoulder, only on a march he may have them carried by a soldier. If the ensign is killed, then the captain is to carry the colours in his stead.
ENTABLATURE, in architecture, is that part of an order of a column, which is over the capital, and comprehends the architrave, frieze, and cornice.
ENTAIL, in law, signifies fee-tail, or fec-intailed. See Estate.
ENTIERTIE denotes the whole, in contradistinction to moiety, which denotes the half j and a bond, damages, Ne. are said to be entire when they cannot be apportioned.
ENTIRE tenancy, signifies a sole possession in one man.
ENTOMOLOGY is that branch of natural history that treats of insects. The study of insects has sometimes been ridiculed as unworthy the attention of men of science; for this, however, there is no just reason j though inferior in point of niagiii
tude, yet they surpass, in variety of structure and singularity of appearance, all the larger branches of the animal world. No one can examine with an attentive eye the subjects of this branch of science without surprise; the great variety of forms, the nice adaptation of their parts to the situation in which each happens to be placed, may excite the amazement of the curious and intelligent mind. The same power and wisdom which are manifested in the order, harmony, and beauty of the heavenly bodies, are equally shewn in the formation of the minutest insect; each has received that mechanism of body, those peculiar instincts, and is made to undergo those different changes, which fit it for its destined situation, and enable it to perform its proper functions. The utility of many insects, either in their living or dead state, as the bee, the crab, the silk-worm, cochineal insect, (see Apis, Coccus, &c,) renders them interesting and important; besides, though diminutive in point of size, they are, in regard to numbers, unquestionably the most distinguished of the works of nature; they are to be found in every situation, in water, in air, and in the bowels of the earth; they live in wood, upon animals, decayed vegetables, and all kinds of flesh, and in every state of its existence down to the most putrid.
The general characters by which insects are distinguished are the following: they are furnished with several, six or more, feet; the muscles are affixed to the internal surface of the skin, which is a substance more or less strong, and sometimes very hard and horny; they do not breathe like larger animals, by lungs or gills situated in the upper part of the body; but by a sort of spiracles, distributed in a series or row on each side the whole length of the abdomen; these are supposed to communicate with a continued chain, as it were, of lungs, or something analogous to them, distributed throughout the whole length of the body, the head is furnished with a pair of what are termed antennae, or horns, which are extremely different in different tribes, and which, by their structure, &c, form a leading character in the institution of the genera into which insects are divided.
Writers on natural history formerly included snails, worms, and the smaller animals, or animalcules, in general, among insects: these are now more properly placed among the tribe vermes, or worm-like animals. Insects have also been denominated bloodless animals, which modem discoveries have shewn to be contrary to feet: some of them, as the cimex lectularius, have been frequently used with the microscope, to exhibit in a striking manner the circulation of the blood. In this insect, with a good glass, the vibrations and contractions of the arteries may be distinctly observed.
Most insects are oviparous; of course, the first state in which insects appear is that of an ovum or egg. This relates to the generality of insects, for there are some examples of viviparous insects, as in the genera Aphis, Musca, &c. From the egg is hatched the insect in its second or caterpillar state; this second state has been usually known by the name of eruca, but Linnaeus has changed it to that of Larva, which see; considering it as a sort of masked form or disguise of the insect in its complete state. The larvae of insects differ \ery much from each other, according to the several tribes to which they belong; those of the butterfly and moth tribe (phaitems) are generally known by the name of caterpillars; those of the beetle (sears bxus), except such as inhabit the water, are of a thick, clumsy form. The larvae of the locust, or grasshopper, (gryllus), do not differ very much in appearance from the complete insect, except being without wings. The larvae of flies, bees, (musca, apis,) Sec. are generally known by the name of maggots, and are of thick short form. Those of water-beetles (dytiscus) are of highly singular forms, and differ, perhaps, more from that of the complete insect than any others, except those of the butterfly tribe. Some insects undergo no change of shape, but are hatched from the egg complete in all their parts, and they undergo no farther alteration than that of casting their skin from time to time, till they acquire the complete resemblance of the parent animal. In the larvae state most insects are peculiarly voracious, as in many of the common caterpillars. In their perfect state some insects, as butterflies, are satisfied with the lightest nutriment, while others devour animal and vegetable substances with a considerable degree of avidity. When the larvae is about to change into the chrysalis or pupa state, it ceases to feed, and having placed itself in some quiet situation, lies still for several hours, and then, by a sort of effort, it divests itself of its external skin, and immediately appears in the different form of a chrysalis or pupa;
in this state likewise, the insects of different genera differ almost as much as the larva. In most of the beetle tribe it is furnished with short legs, capable of some degree of motion, though very rarely exerted. In the butterfly tribe it is destitute of legs: but in the locust tribe it differs very little from the perfect insect, except in not having the wings complete. In most of the fly tribe it is perfectly oval, without any apparent motion or distinction of parts. The pupa of the bee is not so shapeless as that of flies, exhibiting the faint appearance of limbs. Those of the dragon-fly (libelhua) differ most widely from the appearance of the complete insect; from the pupa emerges the insect in its ultimate form, from which it never changes, nor receives any further increase of growth.
Different naturalists have attempted to arrange insects into families and genera, particularly the celebrated Linnaeus, whose arrangement may be thus explained. He has formed them into seven families or orders, composing his sixth class of animals, Iq. secta: he defines an insect, a small animal, breathing through pores on its sides, furnished with moveable antennae and many feet, covered with either a hard crust or a hairy skin. As introductory to the distinguishing marks of the orders and genera, it will be necessary to enumerate and explain the terms given to the different parts, and the most remarkable of the epithets he has applied to them. The body is divided into head, trunk, abdomen, and extremities.
I. Caput, the head, which is distinguishable in most insects, is furnished with eyes, antennae, and most frequently with a mouth; the eyes, two, four, six, or eight in number, destitute of eye-lids, are either small and simple; or large, compound, and hemispherical ; or polyedral; they are commonly immoveable; they are called stipitati, when placed on a stalk. The antenna? are two articulated moveable processes, placed oi the head; they are either, l. Setacea, setaceous, i. e. like a bristle, when they taper gradually from their base, or inserted into the head to their point, f. Clavate, cla vated, 1.1. clnb-«haped, when they grot gradually thicker from their base to their point 3. Filiformes, filiform, «. e. threat shaped, when they are of an equal thick ness throughout the whole of their IcngtJ 4. Moniliformes, moniliform, t. e. of tk form of a necklace, when they are of ai equal thickness throughout, but firmed if a series of knobs, resembling a firing cf