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1most common species in Europe is the E. livida, which is a brownish fiy; the wings are transparent, with dark veins. They are obst rved in fields and gardens. E. borealis is of a more slender form than the common window fly, and of a blackish colour, with large, broad, oval wings, of a brown colour, and rufous legs varied with black. EMPLAS I RUM, in pharmacy, a composition for external use, generally spread upon leather, linen, or some other convenient thing, before it is applied. See Phanxi acy. The following is a recipe for making the Ladies Court Plaster: “Dissolve five ounces of isinglass in a pint of water, aud having ready a quantity of thin black sarsenet, stretched in a proper frame, apply the solution warm with a brush equally over the surface. This is to be repeated, after it is dry, two or three times.” Some give it a coat of gum benzoin dissolved in alcohol; but this is injurious rather than beneficial. EMPLEURUM, in botany, a genus of the Monoecia Tetrandra class and order. Natural order of Aggregatae. Rutaceae, Jussieu. Essential character : male, calyx four-cleft; corolla none : female, calyx four-cleft, inferior ; corolla none ; stigma cylindric, placed on the lateral toothlet of the germ ; capsule opening on the side ; sced one, arilled. There is but one species; viz. E. serrulatum, Cape empleurum. This is a shrub, with wand-like, even branches ; leaves like those of a willow, alternate, subpetioled, linear lanceolate, even above, beneath longitudinally wrinkled ; peduncles few-flowered, lateral, much shorter than the leaves; flowers small, most of them male ; capsules usually solitary, incurved with a beak of the same length. EMULSION, a milky looking fluid, caused by an imperfect combination of oil with water, by means of inucilage, gluten, &c. All oily farnaceous seeds, as nuts, almonds, linseed, &c. form an emulsion by trituration with water; yolk of egg, which is a natural compound of oil an albumen, makes a similar emulsion. ENAMELLING. Neri on glass, with the notes of Merret and Kunckel, afford a variety of good receipts for making enamels, though much still remains to be done in this art. The art is indeed retarded by the considerable advantages the enameller derives from the discovery
of any colour uncommonly brilliant, clear, or hard. On this account the artist naturally endeavours to keep his process a secret, as the source of private gain. The principal ingredients of enamel colours are, however, well known. There are two kinds of enamel; the opaque and the transparent. Transparent enamels are usually rendered opaque by adding putty, or the white oxide of tin, to them. The basis of all enamels is therefore a perfectly transparent and fusible glass. The oxide of tin renders this a beautiful white, the perfection of which is greater when a small quantity of manganese is likewise added. If the oxide of tin be not sufficient to destroy the uransparency of the mixture, it produces a semi-opaque glass, resembling the opal. Yellow enamel is formed by the addition of oxide of lead or antimony. Kunckelikewise affirms that a beautiful yellow may be obtained from silver. Red enamel is formed by the oxide of gold, and also by that of iron. The former is the most beautiful, and stands the fire, which the latter does not. Oxide of copper affords a green, manganese a violet, cobalt a blue, and iron a very fine black. A mixture of these enamels produces a great variety of intermediate colours, according to their nature and proportion. in this branch of the art the coloured enamels are soicetimes mixed with each other, and sometimes the oxides are mixed before they are added to the vitreous bases. The enameller who is provided with a set of good colours is very far from being in a situation to practise the art, unless he be skilled in the methods of applying them, and the nature of the grounds upon which they are to be laid. Many of the mctals are too fusible to be enamelled, and most of them are corroded by the action of the fused glass. For this reason none of the metals are used but gold, silver, and copper. Platina has indeed been used; but of its effects and habitudes with enamel very little can be said, for want of a sufficient number of experiments. The purest gold, of 24 carats, is calculated to produce the best effect with ena. mel. 1. Because it entirely preserves the metallic brilliancy, without undergoing any oxidation in the fire. 2. Being less fusible, it will admit of a more refractory, and consequently a harder and more beautiful enamel. It is not usual, of 18 carats were used.
However, to enamel on finer gold than 22 carats; and the operation would be very defective, if a coarser kind than that For in this case more alkali must be added to the enamel, to render it more fusible, and this addition would, at the same time, render it softer and less brilliant. Rejecting all these exceptions, the following description may be taken, by way of example, or fixing a transparent blue enamel upon gold of 22 carats. The artist begins his operation by breaking his enamel into small pieces in a steel mortar, and afterwards pulverizing it in a mortar of agate. He is careful to add water in this part of the process, which prevents the splinters of glass from flying about. There are no means of explaining the point at which the trituration ought to be given up, as this can be learned only by experience. Some enameis require to be very finely triturated; but others may be used in the form of a coarse powder. As soon as he apprehends that his enamel is sufficiently pounded, he washes it by agitation in very clear water, and pouring of the fluid as it becomes turbid. This process, which is made for carrying of dust and every other impurity from the enamel, is continued until the water comes off as clear as it was poured on. The workman puts his enamel thus prepared into a Wi. earthern or china saucer, with water poured on it to the depth of about one tenth of an inch. He afterwards takes up the enamel with an iron spatula as equally as posible. As the enamel here spoken of is transparent, it is usual to ornament the gold with rose work, or other kinds of work, calculated to produce a good effect through the enamel. The thickness of this first layer depends entirely upon its colour: delicate colours n general require that it should have no great thickness. The moist enamel, being thus placed, is dried, by applying a very clean halfworn linen cloth to it, which must be very carefully done, to avoid removing the enamel by the action of wiping. In this state the piece is ready for the fire. If it be enamelled on both sides, it is placed upon a tile, or iron plate, hollowed out in such a manner, that the uncovered edges of the picce alone are in contact with the support But if it be enamelled on one side only, it is simply laid upon the plate, or upon a tile. Two things, however, require to be attended
cers. The work is place
to. 1. If the work be very small, or not capable of being enamelled on the opposite side, the iron plate must be perfectly flat, in order that the work may not bend when softened by heat. 2. If the work be of considerable size, it is always counter-enamelied, if possible ; that is to say, an enamel is applied on the back surface, in order to counteract the effect which the other coating of glass might produce on the soft metal, when it came to contract by cooling. The enameller's furnace is square, and built of bricks, bedded in an earth proper for the purpose. It may be considered as consisting of two parts, the lower part which receives a muffle resting on the floor of the furnace, and open on both sides. The upper part of the furnace consists of a fire-place, rather larger and longer than the dimensions of the muffle. The fire-place contains the muffle, and must surround it on all sides, except at the bottom. The charcoal is put in at a door above the muffle, which is closed as soon as the fire is lighted. A chimney proceeds from the summit of the furnace, with a moderate aperture, which may be closed at the pleasure of the artist, by applying a cast iron plate to it. This furnace differs from that of the assayer, in the circumstance that it is suplied with air through the muffle itself: or if the draught were beneath the muffle, the heat would be too strong, and could not be stopped when requisite. As soon as the fire is lighted, and the muffle has acquired the requisite degree of ignition, the charcoal is disposed towards the lower part of the muffle, in such a manner as that it shall not fall upon the work, which is then conveyed into the muffle, with the greatest care, upon the plate of iron or earthen-ware, which is taken out by of spring pin:as in eat as possible at the farther extremity of the muffle ; and as soon as the artist perceives a commencement of fusion, he turns it round with great delicacy, in order that the fusion may be very uniform. And as soon as he perceives that the fusion has entirely taken place, he instantly removes it out of the furnace : for the fusion of gold happens so very near to that of the enamel, that the neglect of a few seconds might be attended with considerable loss. When the work is cooled, a seond coat of enamel is applied in the same manner as the first, if necessary. This, and the same cautious management of the fire, are to be repeated for every additional coat of enamei the nature of the work may demand. As soon as the number of coatings are sufficient, it becomes necessary to give an even surface to the enamel, which, though polished by the fire, is nevertheless irregular. This is done with a fine grained Lancashire sile and water. As the file wears sinooth, sand is used. Much precaution and address are required in this part of the work, not only because it is easy to make the enamel searate in splinters from the metal, but ikewise because the colour would not be uniform, if it were to be ground thinner at one part than at another. 'i ne deep scratches of the file irre in the next place taken out by rubbing the surface with a piece of deal wood and fine sand and water. A polish is then given by a second ignition. This polish, however, is frequently insufficient, and not as perfectly uniform as the delicacy of the work may require. The substance used by the enamellers as a polishing material is known by the name of rotten-stone, which is prepared by pounding, washing, decanting of the turbid water, sutiering the fine suspended particles to subside from this water, and lastly levigating it upon a glass plate. The work is then cemented to a square piece of wood, with a mixture of resin and brickdust, and by this means fixed in a vice. The first operation of polishing is made by rubbing the work with routenstone upon a small straight bar of pewter. Some delicacy is here required, to avoid scratching or producing flaws in the enamel by pressing too hard In this way the piece is rendered perfectly even. But the last brilliant polish is given by a piece of deal wood and the Saine rotten-stone. This is the general method of applying enamel ; but some colours require more precaution in the management of the fire. Opaque colours require ess management than the transparent. A variety of circumstances must be attended to in transparent colours; every colour re-quires gold of a particular fineness. When different colours are intended to be placed beside one another, they are kept separate by a small edge or prominency, which is teft in the gold for that purpose, and is polished along with the enamel. The enamelling upon silver is effected
nearly in the same manner as that of gold , but the changes sustained by the colours upon silver by the action of the fire are much more considerable than when gold is used. Copper is not much used by enamel. lers, on account of the difficulty which attends the attempt to fix beautiful colours upon it. When this metal is used, the common practice is, to apply a coating of opaque white enamel, and upon this other colours which are more fusi. ble than the white. A good effect is produced in toys by leaving part of the gold bare. For this purpose its surface is cut into suitaole compartments by the engraver. This, however, is an expensive method, and is for this reason occasionally umitated, by applying small and very thin pieces of gold upon the surface of the enamel, where they are fixed by the fire, and af. terwards covered by a transparent wi. treous coating. A method of taking off the enamel from any toy, without injuring the metal. lic part, is often a desirable object. For this purpose a mixture of common salt, nitre, and alum in powder, is applied upon the enamel, and the piece is put into the furnace. As soon as the fusion has taken place, the piece is to be suddenly thrown into water, which causes the enamel to fly of either totally or in part. Any part which may still remain is to be removed by repeating the same operation a second time. To coat vessels of iron or copper for culinary purposes with an enamel capable of defending the metal from the action of any solvent, and for enduring any heat, or transition from heat to cold, appears a desirable object ; and many experiments have been made on the subject by Mr. Soen Rinman of the Royal Academy of Stockhlom. The following compositions he found answer very well on copper. 1. The white semi-transparent fluor spar and sulphate of lime, in equal quantities, powdered, mixed, and calcinated in a white heat; then powdered, made into a thin paste with water, and applied a little warm to the vessel, also warmed. Then dried and heated gradually to a certain point, a very strong, heat, greater than is generally obtained in an assaying furnace, is to be applied as quickly as possible. 2. Sixty parts of lime, one hundred of fluor spar, sixty of gypsum, twenty of quartz, and one of manganese, are calcinated, ground, and applied in a similar manner, 3. Four parts of fluorspar, four of gypsum, and one of litharge, melted into a straw-coloured glass, ground and applied in the same way, required a much stronger heat. 4. Five parts of fluor spar, five of gypsum, two of minium, two of flint glass, half a part of borax, the same of oxide of tin, and one-twenty-fifth of a part of oxide of cobalt, melted together, made an *namel, which, when ground and applied as the others, fused with a less degree of heat. This, M. Rinman imagines, would have been acted upon in length of time by sulphuric acid. The oxide of cobalt was prepared by saturating a solution of cobalt in aqua-fortis with common salt, and evaporating to dryness. As these would not do for iron, he tried the following : 1. minium, nine Ports; flint glass, six; pure potash, two; nitre, two; borax, one; were ground together, put into a covered crucible, which they only half filled, and fused into glass. This poured out on a piece of marble, quenched in water, powdered and made into a thin paste, was laid on both sides of an iron vessel. After having been dried and heated gradually, the vessel was put under a muffle, well heated in an assaying furnace, and in half a minute the enamel melted. The vessel being then withdrawn, was found ena. melled of a beautiful black colour, which appeared to be owing to a thin layer of oxided iron seen through the transparent glaze. 2. The same, with one hundreth part of oxide of cobalt prepared *above, covered the vessel more persectly with a blue enamel. 3 the same, ground with potters’ white lead, which $onsists of four parts of lead and one of * produced a very smooth grey enamel more firm and hard than the preceding. A small }. of red oxide of iron $ove it a fine dark red colour. 4. Flint §lass, twelve parts; minium, eighteen ; *h, four; nitre, four ; borax, two *de of tin, three, oxide of cobalt, "...tighth of a part, gave a smooth peari o ensmel, not brittle or subject **k, ane capable of enduring sud. en changes of heat and cold, as well as o Gf oils, alkalies, and weak ... W \o cannot resist the stronger
ho enamels were applied only on to lo iron, cast iron being too thick Butth **ted with sufficient quickness. Cast § have been applied to the thin
"*els in England. It seems unne.
cessary to add, none of them will bear hard blows; and this is perhaps the reason why they have not been more used with us. The application of enamel colours to glass or earthenware constitutes a peculiar branch of the art. M. Broughiart, of the porcelain manufactory at Sévres, has given a good account of them. (Nicholson's Journal, Vol. III. 4to.) These bodies may be divided into three very distinct classes, from the nature of the substances that compose them, the effects produced on them by the colours, and the changes they undergo. These are, 1... enamel ; soft porcelain, and all the glazes, enamels, or glasses, which contain lead in any considerable quantity. 2. Hard porcelain, or such as is glazed with feldspar. 3. Glass, in which there is no lead, such as the common window glass. The principles of composition of these colours, and the general phenomena they present on these three grounds or supporters, are regularly treated of. Colours in enamel painting have been longest known. Enamel is a glass rendered opaque by oxide of tin, and very fusible by the oxide of lead. It is this last, which, in particular, gives it properties very different from those of the other excipients of metallic colours. Hence all the glasses and glazes which contain lead have the properties of enamel, and what we may assert of the one will apply to the other with very little difference. Such are the white and transparent glazes of Dutch or Delf ware; and the glaze of the porcelain called software. This porcelain, the first made in France, particularly at Sévres, and indeed for a long time almost exclusively at that manufactory, has for its base vitreous frit, nearly opaque, capable of being acted upon by marle, and its glaze is very transparent glass, containing much lead. The colours made use of are the same as those for enameling consequently the changes these colours undergo in enamel must take place in this species of porcelain : the causes of the change being the same in both. The colours for enamel and soft porcelain require less flux than the others, because the glass on which they are placed softens sufficiently to be penetrated by them. This solvent may be either the mixture of glass of lead and pure silex, calledrocaille, or this same glass mixed with that of borax.
Montamy says, that glass of lead ought not to be used in the flux or enamel ; he employs borax alone. He then dilutes or makes up his colours in a volatile oil. On the contrary, the painters of the manufactory at Sévres use only colours without borax, because they dilute them with gum, and borax does not dilute them well this way. M. Brougn art is convinced that both methods are equally good, and that Montainy is not justified in excluding the fluxes of lead, as they are employed without inconvenience every day, and even render the management of colours more easy. It is remarked, that in the baking of these colours the glaze is softened so much as to be easily penetrated by them; and this is one great cause of the change they undergo. They become diluted by the mixture with the glaze, and the first fire changes a painting, apparently finished, into a very slight sketch. The oxide of lead contained in the glaze is a more powerful cause of the great changes these colours undergo. Its destructive action is principally exercised on the reds of iron, and is very remarkable. It has already been shewn that the two |. causes of the change, which coours on enamel and tender porcelain undergo, do not relate to the composition of these colours, but entirely to the nature of the glass on which they are placed. The assertion that the colours of porcelain are subject to considerable change, relates to the colours of soft porcelain, a species of ware now almost totally abandoned. Hence it follows, that the paintings of porcelain require to be several times retouched and burned, in order to possess the necessary strength. Though these paintings have always a certain softness, they are constantly more brilliant, and never subject to the inconvenience of scaling off. Hard porcelain is the second species of ground or excipient for the metallic colours. It is known that the base of this porcelain is a very white argil, called kaolin, mixed with a siliceous and calcareous solvent, and the glaze is nothing but feldspar fused without an atom of lead. This porcelain, which is that of Saxony, is of a much later date at Sévres than the soft or tender. The colours employed are of two kinds; the first, used for representing different objects, are baked with a very inferior fire to that required
for baking the porcelain itself. They are very numerous and varied The others, which require to be fused at as great a heat as that for baking the porcelain, are laid on the general surface. They are much less numerous. The colours for painting are made up very nearly of the same materials as those for tender porcelain; they only contain more flux. This flux is compossd of the glass of lead (called rocaille) and of borax. M. Brougniart asserts, that he has not met with any work that treats of the composition, use, and effects of these colours. In fact, it has no where been asserted, in print, that all these colours, except one, are unchangeable in fire; whereas it has been often asserted, in books, that paintings in enamel are subject to considerable change. When the porcelain is put into the fire to bake the colours, the feldspar glaze dilates and opens in pores, but does not become soft. As the colours do not penetrate it, they are not subject to the changes they undergo on tender porcelain. It must, however, be observed, that they lose a little of their intensity by acquiring the transparence given them by the fusion. When works of little importance are made, they need not be retouched; but this is necessary when a painting is to be highly finished. This retouching is not more distinguishable in paintings on porcelain, than in that of any other species of painting. One of the great inconveniences of these colours is, that they scale or fly off when the fire is often applied. This has been particularly remarked at Sévres, on account of the solidity and infusibility with which porcelain is there manufactured. But these qualities cause it to resist the alterations of heat and cold for a longer time, and give its ground a more brilliant colour. On the other hand, the porcelains of Paris being more vitreous, transparent, and of a bluish cast, generally crack, if boiling water is frequently poured into them. In order to remedy this evil, without altering the quality of the body, Brougniart softens the glaze a little, by introducing more siliceous or calcareous flux, according to the nature of the feldspar. This method succeeded, and for twelve months then past the colours had past two and three times through the fires, without cracking, provided there were not too much flux, and they were not laid on too thick.