Imágenes de páginas

tural order of Personate. Vitices, Jussieu. Essential character: calyx five-tootlied, teeth acuminate; corolla two-lipped; stamina four, with two barren anthem at the end of the shorter filaments; pericarpium a drupe containing four or five celled nut, with a seed in each cell. There are two species.

GIANTs causeway, a vast collection of a black kind of marie, called basaltes, in the county of Antrim, in Ireland. See Basaltes, and Staffa.

GIBBOUS, in astronomy, a term used in reference to the enlightened parts of the moon, whilst she is moving from the first quarter to the full, and from the full to the last quarter: for all that time the dark part appears horned, or falcated; and the light one hunched out, convex or gibbons.

GIFT, in law, a transferring the property in a thing from one to another without a valuable consideration ; for to transfer any thing upon a valuable consideration, is a contract or sale. He who gives any tiling is called the donor, and he to whom is given is called the donee. By the common law all chattels, real or personal, may be granted or given without deed, except in some special cases, and a free gift is good without a consideration, if not to defraud creditors. But no leases, estates, or interests, either of freehold or term of years, on any uncertain interest, not being copyhold or customary interest of, in, to, or out of any messuages, manors, lands, tenements, or hereditaments, shall at any time be assigned, granted, or surrendered, unless it be by deed or note in writing, signed by the party so assigning, granting, or surrendering the same, or their agents thereunto lawfully authorized by writing, or by act and operation of law. 29 Car. II. c. 3. A gift of any thing, without a consideration, is good, but it is revocable before delivery to the donee, of the thing given.

GILBERTIA, in botany, a genus of the Decandria Monogynia class and order. Calyx five-toothed ; corolla deeply five-parted ; nectary deeply ten-parted, with lanceolate segments; anther* sessile, in the segments of the nectary; fruit six-celled. Only one species, G. racemosa, found in Peru; branches reddish and downy ; leaves alternate, elliptic, acute, entire, reddish, downy underneath; racemes axillary. G 11.1), or Guild. See Giii.d. GILDING, art of. The art of gilding or of laying a thin superficial coating of metal on wood, metal, and other substances, has VOL. III.

been long practised and highly esteemed, both for its utility and the splendid effect which it produces. Gold, from the extreme beauty of its colour, and from the length of time during which it may be exposed to the action of the air without tarnishing, is perhaps the most valuable of all substances for the purpose of decoration ; but on account of its dearness and weight, it can very seldom be employed in substance, and its ornamental use would be limited, indeed, if it were not at the same time the most extensible of all substances; so that a given weight of gold, notwithstanding its high specific gravity, may, by beating, be made to cover a larger surface than an equal quantity of any other body. Among the ancients, the Romans, and among the modems, the French have been remarkable for their large and profuse consumption of gold ; not only the temples, theatres, and other public buildings, being adorned with gilding, but even the private houses of the wealthier classes.

The materials for gilding, or rather the different states in which gold is used for the purpose, are the following: leaf-gold of different thicknesses, and formed either of the pure metal, or of an alloy of this with silver, amalgam of gold, and gold-powder. The leaf-gold is procured by the gilder from the gold-beater, for an account of which we shall refer the reader to the article Gold; but the other two substances being prepared by the gilder himself, may be with propriety described here. The amalgam of gold is made, by heating in a crucible some pure quicksilver; and when it is nearly boiling, adding to it about a sixth of its weight of fine gold in thin plates, heated red hot; the mixture, after being kept hot for a few minutes, becomes of a perfectly homogeneous consistence, and may then be allowed to cool: when cold, it is to be put in it piece of soft leather, and by gradual pressure, the fluid part of the amalgam, consisting almost wholly of mercury, may be forced through the pores of the leather, while the gold combined with about twice its weight of mercury will remain behind, forming a yellowish silvery mass of about the consistency of soft butter. This, after being Ju-uised in a mortar, or shaken in a strong phial, with repeated portions of salt and water, till the water ceases to be fouled by it, is fit for use, and may be kept for any length of time without injury in a corked pbial. It is of essential importance that the materials of this amalgam, and especially the mercury, V

should be perfectly pure, as the least portion of lead or bismuth would very materially injure the beauty of the gilding, by detcuorating the colour of the gold, and filling it with black specks ; on this account no mercury ought to be employed that has not been procured by distillation from the red precipitate (nitrons red oxide of mercury) either alone or mixed with a little charcoal powder.

Gold is prepared in three different ways. The first and simplest is to put into a glass or iMi liiriii mortar some gold-leaf, with a little honey or thick gum-water, and grind the mixture for a considerable time, till the gold is reduced to extremely minute fragments; when this is done, a little warm water will wash out the honey or gum, leaving the gold behind in a flaky pulverulent state. A less tedious and more effectual way of comminuting the gold, is to dissolve it in nitro-miiriate acid, and then precipitate it with a piece of copper: the precipitate, after being digested in distilled vinegar, and then washed in water and dried, is in the form of a very fine powder, and both works better, and is easier to burnish than the ground leaf-cold. The finest ground gold is however produced by heating very gradually the gold-amalgam in an open earthen vessel, and continuing the fire till the whole of the mercury is evaporated, taking care that the amalgam shall be constantly stirred with a piece of glass, rod, or tobacco-pipe, in order to prevent the particles of gold from adhering as the mercury flies off. When the mercury is completely evaporated, the residual gold being then ground in a Wedgewood-ware mortar, with a little water, and afterwards dried, it is fit for use.

Gilding is performed either with or without beat. By the first of these methods those substances are gilt which are not liable to alteration by exposure to i moderate heat, such as metals, and sometimes glass and porcelain: the second method is practised with those substances, such as wood, paper, lead, silk, lacquered and japanned ware, &c. which would be injured and even destroyed at the temperature requisite for gilding the former. The last of these methods being the simplest, shall be first described, and we shall' begin with the art of gilding on wood.

There are two methods for gilding on "wood, namely, oil gilding and burnished gilding. Oil gilding is thus performed : the wood must first be covered, or pruned? with

two or three coatings of boiled linseed ori and white-lead, in order to fill up the pore. and to conceal the irregularities of the surface, occasioned by the veins in the wood. When the priming is quite dry, a thin coat of gold-size must be laid on. This is prepared by grinding together some strongly calcined red ochre with the thickest drying oil that can he procured, and the older the better: that it may work freely, it is to be mixed previously to being used with a little oil of turpentine, till it is brought to a proper consistence. If the gold-size is good, it will be sufficiently dry in twelve hours, more or less, to allow the artist to proceed to the last part of the process, which is the application of the gold. . Fortius purpose it leaf of gold is spread on the cushion (formed by a few folds of flannel secured on a piece of wood, about eight inches square, by a tight coveriug of leather), and is cut into strips of a proper size by a blunt pallet-knife; each strip being then taken up on the point of a fine brush, is applied to the part intended to be gilded, and is then gently pressed down by a ball of soft cotton; the gold immediately adheres to the sticky surface of the size, and after a few minutes the dexterous application of a large camels' hair brush sweeps away the loose particles of the gold leaf without disturbing the rest. In a day or two the size will be completely dried, and the operation is finished. The advantages of this method of gilding are, that it is very simple, very durable, not readily injured by changes of weather, even when exposed to the open air, and when soiled it may be cleaned by a little warm water and a soft brush: its disadvantage is, that it cannot be burnished, and therefore wants the high lustre produced by the next method. Its chief employment is in outdoor work.

Burnished gilding, or gilding in distemper, is thus performed. The surface to be gilt must be carefully covered with strong size, made by boiling down two pieces of white leather, or clippings of parchment, till they are reduced to a stiff jelly, this coating being dried, eight or ten more must be applied, consisting of the same size, mixed with fine Paris-plaster or washed chalk; when a sufficient number of layers have been put on, varying according to the nature of the work, and the whole is become quite dry, a moderately thick layer must be applied, composed of size and bole, or yellow ochre: while this last is yet moist, the gold leaf is to be put on In the usual manner; it will immediately adhere on being pressed by the cotton ball, and before the size is become perfectly dry, those parts Which are intended to be the most brilliant are to be carefully burnished with agate or dog's-tooth. In order to save the labour of burnishing, it is a common, but bad practice, slightly to burnish the brilliant parts, and to deaden the rest by drawing a brush over them dipped in size: the required contrast between the polished and the unpolished gold is indeed thus obtained ; but the general effect is much inferior to that produced in the regular way, and the smallest drop of water tailing on the sized part occasions a stain. This kind of gilding can only be applied on in-door work, as rain, and even a considerable degree of dampness, Will occasion the gold to peel off. When dirty, it may be cleaned with a soft brush, and hot spirit of wine, or oil of turpentine. It is chiefly used on picture frames, mouldings, and stucco.

Letters written on vellum or paper are gilded in three ways: in the first, a little size is mixed with the ink, and the letters are written as usual; when they are dry, a slight degree of stickiness is produced by breathing on them, upon which the gold leaf is immediately applied, and by a little pressure may be made to adhere with sufficient firmness. In the second method, some white-lead or chalk is ground up with strong size, and the letters are made with this by means of a brush: when the mixture is almost dry, the gold leaf may be laid on, and afterwards burnished. The last method is, to mix up some gold powder with size, and make the letters of this by means of a brush. The edges of the leaves of books are gilded, while in the binder's press, by first applying a composition formed of four parts of Armenian bole, and one of sugar candy, ground together to a proper consistence, and laying it on with a brush with the white of egg: this coating, when nearly dry, is smoothed by the burnisher; it is then slightly moistened with clean water, and the gold leaf applied, and afterwards burnished. In order to impress the gilt figures on the leather covers of books, the leather is first dusted over with very fine rezin, or mastich, then the iron tool by which the figure is made is moderately heated, and pressed down on a piece of leaf gold which slightly adheres to it, being then immediately applied to the surface of the leather with a certain force, the tool at the earned time makes an impression, and melts

the mastich which lies between the heated iron and the leather; in consequence of this the gold with which the face of the tool is covered is made to adhere to the leather, so that on removing the tool a gilded impression of it remains behind.

Drinking glasses and other utensils of this material, are sometimes, especially in Germany, gilt on their edges: this is done in two ways, either by a simple adhesive varnish or by means of fire. The varnish is prepared by dissolving in drying linseed oil, a quantity of gum amine, or still better of clear amber, equal in weight to the linseed oil; a very drying and adhesive varnish is thus prepared, which being diluted with a proper quantity of oil of turpentine is to be applied as thin as possible to those parts of the glass which are intended to be gilded; when this is dry, which will be about a day, the glass is to be placed by the fire side, or in a stove till it is so warm as'almost to burn the fingers when handled; at this temperature the varnish will become glutinous, and a piece of gold leaf applied in the usual way will immediately adhere; when the gilding is thus put on, and before it is grown quite cold it may be burnished, taking care only to interpose a piece of very thin paper betwen the gold and the burnisher. If the varnish is very good this is the best method of gilding glass, as the gold is thus fixed on more evenly than in any other way: it often happens, however, that when the varnish is but indifferent, that by repeated washing the gold soon wears off: on this account the practice of burning it in, is sometimes had recourse to.

For this purpose some gold powder is tempered with borax, and in this state applied to the clean surface of the glass, with a clean camels' hair pencil; when quite dry the glass is put in a stove heated to about the temperature of an annealing oven, the gum bums off, and the borax by vitrifying cements the gold with great firmness to the glass; after which it may be burnished. The gilding upon porcelain is in like manner fixed by fire and borax; and this kind of ware being neither transparent nor liable to soften, and thus injure its form in a low red heat, is free from the risk and injury, which the finer and more fusible kinds of glass are apt to sustain from such treatment.

All the methods of gilding hitherto described resemble each other by being ar complished by means of some adhesive medium; this, how ever, is not the case with gilding upon metals, the gold is brought into immediate contact with the other metal and they both remain firmly united merely by the attraction of adhesion subsisting between them. The simplest of all the kinds of gilding on metal, and which strikingly demonstrate the power of the affinity of adhesion, is one which is sometimes practised on plane surfaces of copper and iron, with considerable success. The metal being previously polished is heated to about the temperature of melted lead, and covered with a double layer of gold leaf: by the cautious application of a blood stone burnisher applied gently at first, and increasing the force of the pressure by degrees, the surface of the gold and copper are brought to touch each other in almost every point, and then adhere with a force proportionate to the completeness of the contact. The first layer being thus burnished down, a second is made to adhere in the same manner, and sometimes a third, if the gilding is intended to be very solid; The objection to this kind of gilding is its tediousness and the almost impossibility of using a sufficient pressure without injuring the evenness of the gilded surface: where these objections do not apply there cannot be a more effectual mode of gilding as is evident from the manufacture of gilt silver and copper wire. The bar, before it is committed to the wire-drawer, is plated with gold, by having several plates of gold successively burnished down upon it, and being then subjected to the stronger compression which takes place in wire-drawing, the gold and the other metal become sa perfectly united as to form in a manner but one substance.

The most usual method of covering the face of a metal with gold, is by means of an amalgam, or, as it is technically called, water-gilding. If the metal to be gilt is silver, the best method of proceeding is first to soak it in warm dilute muriatic acid, that the surface may be rendered perfectly clean, it must then be washed in clean water, changed two or three times, to get rid of the whole of the acid : being afterwards dried, and made moderately warm, a little gold amalgam, also warm, is to be carefully and evenly spread upon the silver, to which it will immediately adhere: when this is completed, the piece is placed upon a convenient support over a charcoal tire, and while the mercury is evaporating, if any specks or places appear, which have escaped the amalgam, a small piece is to be

laid on, and spread with a brush, to supply

the deficiency, without removing the article from the fire. After a time, the whole of the mercury will be driven off, and the piece, after cooling, being accurately examined, will be found to be entirely covered with a thin coating of pale dull gold. The small roughnesses, and loosely-adhering particles, are now to be removed with a scratchbrush, which is made of some extraordinary fine brass wire, bound together into a tuft; by it the surface is rendered perfectly smooth and bright; but it still remains of a pale yellowish colour: this defect is next removed by warming the piece, and smearing it over with gilders' wax, a composition of bees' wax, red ochre, verdigris, and green vitriol or alum. The wax being burnt off over a charcoal fire, and the piece quenched in urine, the colour of the gilding will be found to be much heightened; if it is not sufficiently so, the application of a succeeding one will complete the desired effect, after which the work may be burnished or not, according to the taste of the artist. Instead of the common gilders'-wax, a mixture of equal parts of nitre, sal-ammoniac, green vitriol, and verdigris, moistened with water, will answer the purpose.

Copper, and the alloys formed by its combination with zinc, are gilded nearly in the same manner as silver; but, as their affinity for mercury is considerably less than that of silver, it would be difficult to make the amalgam of gold adhere to the burnished surface of these metals by the same means, and with the same evenness, as takes place in the last case described. To obviate this inconvenience, advantage is very ingeniously taken of the action of nitric acid to facilitate the adhesion of the copper and mercury, in the following manner. A piece of copper, a button for example, if cleaned, by steeping it in acid, and subsequent washing, and is then burnished either in a lathe, or by any other means: after this it is dipped in a neutralized solution of nitrate of mercury, and in the space of a few minutes, owing to the strong affinity of nitric acid for copper, the mercurial salt is decomposed, the copper takes the place of the mercury, and at the same time the mercury is deposited in the metallic state on the surface of the copper, covering it entirely, and strongly adhering to it; the gold amalgam is now applied, and the rest of the process goes on as already described. By this method of proceeding, a given quantity of gold may be made to cover a larger surface than in any other way of gilding on metals; five grains of gold will completely gild both the upper and under surfaces of one-hundred and forty-four copper buttons each of them an inch in diameter.

There is no metal, the gilding of which presents so many difficulties as iron, or ra• tber steel. If the method of simple burnishing down is had recourse to, the heat requisite for this purpose will, in many cases, bring - the temper of the steel too low: on such occasions, the way already described for gilding on copper, is sometimes practised; that is, the parts of the steel to be gilded, are pencilled over with nitrate of mercury, by which they are covered with a slightly-adhering coat of mercury; then the amalgam is applied, and the gilding finished in the usual way. The objections to this mode of proceeding are, first, that a considerable heat is required, though inferior to that requisite for burnishing down; and secondly, that even with all possible care the gilding is apt to be rough and scale off. A very considerable improvement in this way of gilding is to trace the figure of the gilding on the steel first of all, with a brush charged with a strong solution of sulphated copper, in consequence of which it pretty thick plate of this metal is deposited on the steel, to which it may be made to adhere, with considerable firmness, by means of the burnisher; thus the gilding is, in fact, performed upon the copper.

A new method of gold-gilding upon steel has lately been published, possessed of many advantages over the others, and probably in time may attain to a very high degree of perfection. It depends upon the well-known fact, that if sulphuric ether and nitro-muriate of gold are mixed together, the ether will, by degrees, separate from the acid nearly the whole of the gold, and retain it for some time in solution, in nearly a metallic state. If ether, thus charged with gold, is spread, by means of a pen or fine brush, on the surface of highly-polished steel, the ether presently evaporates, leaving the gold behind in close contact with the steel, and the adhesion is considerably improved by the subsequent application of the burnisher. The dearness, and especially the rapid volatility of ether, are, at first, objections of some moment, but may be got over by using the best oil of turpentine instead of ether, which has nearly the same efficacy in decomposing the nitro-mu

riate of gold, and is both cheaper, and not so very quickly evaporable.

Gold-gilding upon silver is, we believe, at present entirely disused. It was performed in the following manner: a saturated solution of gold, in nitro-muriatic acid, was poured upon some linen rags, and when they were become dry, they were heaped in a plate, and touched with a hot coal. The fire gradually spread through the mass, and reduced it to a heavy black ash. A soft cork, being moistened in water, was dipped in this ash, to which a part of it adhered, and was then rubbed on the surface of polished silver, upon which the minute particles of gold became fixed, and covered it with an extremely thin coating, which, when burnished, exhibited the genuine colour and lustre of the precious metal. Allan's Dist.

GILL, a measure of capacity, containing a quarter of a pint.

GILT garnish. See Varnish. GIMBALS, in sea affairs, the brass rings by which a sea compass is suspended in its box, so as to counteract the effect of the ship's motion, and keep the card horizontal. GIMBLETING, a term applied to the anchor to denote the action of turning it round by the stock, so that the motion of the stock appears similar to that of the handle of a gimblet when it is employed. GIN. See Geneva. Gin, in mechanics, a machine for driving piles, fitted with a windlass and winches at each end, where eight or nine men heave, and round which a rope is reeved, that goes over the wheel at the top.

GINANNIA, in botany, a genus of the Enncandria Monogynia class and order. Natural order of Lomentacea*. Legnniinosa?, Jussieu. Essential character: calyx double, both one-leafed; petals three, fringed, spreading; germ pedicelled, with a membranaceous wing at top; legume. There is but one species, viz. G. guianensis, a shrub about fifteen feet high; a native of the forests of Guiana. GINGER, in botany. See Zinziber. GINORA, in botany, so called in honour of the Marquis Carlo Ginori, a genus of the Dodecandria Monogynia class and order. Natural order of Salicarix, Jussieu. Essential character: calyx six-cleft; petals six, capsule one-celled, four-valved, coloured, containing many seeds. There is but one species, Tie. G. Americana, an elegant little shrub about four feet high; it is

« AnteriorContinuar »