tool, must be explained. In order to decarbonate the surfaces of cast-steel plates, by which they are rendered much softer and fitter for receiving either transferred or engraved designs, pure iron filings, divested of all foreign matters, are used. The stratum of decarbonated steel should not be too thick for transferring fine and delicate engravings; for instance, not more than three times the depth of the engraving; but for other purposes the surface of the steel may be decarbonated to any required thickness. To decarbonate it to a proper thickness for a fine engraving, it is to be exposed for four hours in a white heat, enclosed in a cast-iron box with a wellclosed lid. The sides of the box must be at least three-quarters of an inch in thickness, and at least a thickness of half an inch of pure iron filings should cover or surround the cast-steel surface to be decarbonated. The box is allowed to cool very slowly, by shutting off all access of air to the furnace, and covering it with a layer of six or seven inches of fine cinders. Each side of the steel plate must be equally decarbonated, to prevent it from springing or warping in hardening. The safest way to heat the plates is to place them in a vertical position. The best steel is preferred to any other sort of steel for the purpose of making plates, and more especially when such plates are intended to be decarbonated. The steel is decarbonated to render it sufficiently soft for receiving any impression intended to be made thereon; it is, therefore, necessary that, after any piece of steel has been so decarbonated, it should, previously to being printed from, be again carbonated, or reconverted into steel capable of being hardened. In order to effect this recarbonization or reconversion into steel, the following process is employed; a suitable quantity of leather is to be converted into charcoal, by exposing it to a red heat in an iron retort until most of the evaporable matter is off the leather. The charcoal is reduced to a very fine powder; then take a box made of cast iron of sufficient dimension to receive the plate which is to be reconverted into steel, so as that the interme

diate space between the sides of the box and the plate may be about an inch. Fill the box with the powdered charcoal, and, having covered it with a well-fitted lid, let it be placed in a furnace similar to those used for melting brass, when the heat must be gradually increased until the box is somewhat above a red heat; it must be allowed to remain in that state till all the evaporable matter is driven off from the charcoal; remove the lid from the box, and immerse the plate in the powdered charcoal, taking care to place it so that it may be surrounded on all sides by a stratum of the powder of nearly a uniform thickness. The lid being replaced, the box, with the plate, must remain in the degree of heat before described for from 3 to 4 hours, according to the thickness of the plate so exposed; 3 hours are sufficient for a plate of an inch in thickness, and 5 hours when the steel is 1 inch in thickness. After the plate has been exposed to the fire for a sufficient length of time, take it from the box and immediately plunge it into cold water. Here it is found by experience that the plates, when plunged into cold water, are least liable to be warped or bent when they are held in a vertical position, and made to enter the water in the direction of their length. If a piece of steel, heated to a proper degree for hardening, be plunged into water, and suffered to remain there until it becomes cold, it is found by experience to be very liable to crack or break, and in many cases it would be found too hard for the operations it was intended to perform. If the steel cracks it is spoiled. Therefore, to fit it for use, should it not be broken in hardening, it is the common practice to heat the steel again, in order to reduce or lower its temper. The degree of heat to which it is now exposed determines the future degree of hardness, or temper, and this is indicated by a change of colour upon the surface of the steel. During this heating a succession of shades is produced, from a very pale straw colour to a very deep blue. It is found that, on plunging the steel into cold water, and allowing it to remain there no longer

than is sufficient to lower the tempera- | ture of the steel to the same degree as that to which a hard piece of steel must be raised to temper it in the common way, it not only produces the same degree of hardness in the steel, but, what is of much more importance, almost entirely does away with the risk of its cracking. The proper degree of temperature arrived at, after being plunged into cold water, can only be learned by actual observation, as the workman must be guided entirely by the kind of hissing noise which the heated steel produces in the water while cooling. From the moment of its first being plunged into the water the varying sound will be observed; and it is at a certain tone, before the noise ceases, that the effect to be produced is known. As a guide, take a piece of steel which has already been hardened by remaining in the water till cold, and by the common method of again heating it, let it be brought to the pale yellow or straw colour, which indicates the desired temper of the steel plate to be hardened. By the above process, as soon as the workman discovers this colour to be produced, to dip the steel into water and attend carefully to the hissing which it occasions, he will then be able, with fewer experiments, to judge of the precise time at which the steel should be taken out. Immediately on withdrawing it from the water, the steel plate must be laid upon or held over a fire, and heated uniformly until its temperature is raised to that degree at which a smoke is perceived to arise from the surface of the steel plate after having been rubbed with tallow; the steel plate must then be again plunged into water, and kept there until the sound becomes somewhat weaker than before. It is to be taken out, and heated a second time to the same degree as before, and the third time plunged into water till the sound becomes again weaker than the last; exposed the third time to the fire as before; and for the last time returned into the water and cooled. After it is cooled clean the surface of the steel plate by heating it over the fire. The temper must be finally reduced by bringing on

a brown or such colour as may suit the purpose required. The above is an old process and not generally used. Engraving on steel is effected nowadays by graving and etching like copper; using for biting-in a mixture of 1 part pyroligneous acid, 1 nitric acid, 3 water; run off from the plate in less than a minute, rinse in running water, and dry quickly. Use stronger acid when a deeper tint is required.

Engraving Steel Cylinders.-A cylinder of very soft or decarbonized steel is made to roll, under a great pressure, backward and forward on the hardened engraved plate till the entire impression from the engraving is seen on the cylinder in altorelievo. The cylinder is then hardened and made to roll again backward and forward on a copper or soft steel plate, whereby a perfect facsimile of the original is produced of equal sharpness.

Etching.-The apparatus consists of copper plates, etching needles, hand-rest, etching-ground dabber, oil-rubber, rottenstone, smoking taper, engraver's shade, bordering wax, stopping-out varnish, tracing paper, and aquafortis.

Ground. The ground is composed of equal parts of asphaltum, Burgundypitch, and beeswax; place them in an earthen pipkin in an oven, and melt. The mass must be kept stirred until well incorporated. Pour the mixture into a basin of cold water, and, when nearly cold, it should be pressed, and rolled with the hand until all the water is discharged, then make into a ball. Procure a piece of worn silk, without holes; double it; place the ball therein, and tie up the ends with packthread, taking care that the double silk reaches well and tightly over the ball; cut off the surplus silk, and let the knot remain for a hand-hold.

Dabber.-Take a piece of silk, twice the size of that for the ground ball; double it; place in it a ball of coarse wool well picked out, about the size of a small apple; tie it up in the same way as the ball for the ground, and it is ready for use.

Oil-Rubber. An oil-rubber is made from a strip of woollen cloth, about 2 inches wide, rolled up tightly, and bound over with packthread or thin tape. With

a sharp knife cut off one end, avoiding | the string, so that the surface may be quite flat. This is used for taking out stains, or polishing the plate, as in Fig. 46.

FIG. 46.

Rotten-stone. Take a piece of fine flannel, rather less than the silk which covers the etching-ground ball; double it; place on it a small quantity of rottenstone, in powder, which tie up in a bag. A small portion of fine whiting in the lump should be also kept at hand.

Smoking Taper, or Lamp.-For small plates, procure a wax taper; uncoil it by degrees before the fire until it is all equally pliant; double it up in about six lengths; give it one twist while warm, and turn it a few times before the fire, that the pieces of taper may adhere to each other; melt the wax at one end, so that the wick is exposed; see that all the cotton ends will light freely; care should be taken to extinguish the cotton, or it will revive with the least draught, and may become dangerous. For large plates it is preferable to use an ordinary oil lamp mounted on gimbals; this obviates the inconvenience occasioned by the dripping of the tapers.

Bordering Wax.- 3 oz. of resin, 2 oz. of beeswax, and such a quantity of sweet oil as will soften the mixture to fancy. Procure an earthen pipkin; place in the bottom oz. or more of sweet oil; add the resin and beeswax, broken in small pieces; when melted work the ingredients well together with a stick until thoroughly incorporated; then pour into a basin of cold water; as it gets cold, work it well with the hands by pulling out into lengths and doubling it together again; the more it is worked the better it will be for use. Should it turn out brittle, return it broken to the pipkin, and add more oil; work it well together as before, pour it into water, and work it again with the hands.

wire into a half circle; bind it together with waxed string; lay it on tissue paper; cut away all but an inch round the wire: cover that inch with paste, and turn it over the wire; when dry the shade is complete. Fasten a light string to the centre of the half-circle, and suspend it from the window-latch when in use. This shade must be placed in a forward position, sloping before the plate, and the white light it produces will enable the engraver to see the lines made by the etching needle. An equally effective shade may be made by covering a light square wire frame with tissue paper, and supporting it with two struts. This frame can be made to rest at any angle, upon the table immediately in front of the work.

Hand-Rest.-Any flat and thin piece of wood will answer the purpose, which is to keep the hand clear of the plate whilst at work. A good hand-rest may be made of a thin board raised above the work upon side pieces of such a height as to allow the plate to be freely moved underneath the board. The front edge of the board may be faced with a strip of steel planed true when it serves as a straight-edge. This arrangement will be found extremely handy.

Stopping out Varnish. Turpentine varnish is superior, for several reasons, to Brunswick black.

Turpentine Varnish.-Break small pieces of resin into a phial; pour over spirits of turpentine to about twice the height of the resin. Place the bottle in a small saucepan of water on the hob, near enough to the fire to make and keep the water hot; place a cork lightly in the mouth of the bottle, as the mixture will require to be shaken occasionally. Pour a small portion of this mixture into a small pot, with a little lampblack added to give it a colour, and well mixed. This last is necessary to prevent lumps; it may be done by working the mixture well together with the camel-hair pencil. This is a good stopping-out varnish. With this varnish go over the border or margin of your plate; do this when about to put it away, and the varnish will become hard by being left a night to set. When biting-in

fire is preferable, and a couple of spirit lamps with rests for the corners of the plate, the best plan of all. Be careful not to overheat the plate. If the surface becomes discoloured the plate is over hot; as a test, turn it over and spit on the back; if the moisture jumps off, the plate is sufficiently hot; should it hiss and remain on the plate, more heat must be obtained. A piece of canvas, rather larger than the plate, should be warmed by laying it before the fire during the heating process; place it on the table, and lay upon it the plate retained in the vice. Now pass the ball of ground, Fig. 48, over it backwards and forwards until the plate is covered, spreading the ground as evenly and thinly as possible. Use the dabber with a quick action, pressing it down and plucking it up. If the ground does not distribute itself easily, burn paper under the plate as before until it shines all over, being cautious that the ashes of the paper do not settle on the surface; dab on again, decreasing the pressure, but not the speed of action, until the surface is all over alike.

FIG. 48.

centre, using a fluttering action with the hand, Fig. 50; smoke on until the whole surface is of a dark colour, keeping the taper at such a distance from the plate that the burning cotton may have no chance of touching it, although the flame spreads over it. Another way is to suspend the plate, if of large size, overhead, and smoke with the oil lamp. When the surface is all black alike, and no sooty marks are to be seen on the working part of the plate, the ground is fit for use. Take the plate, face downwards, to some convenient place, and pour cold water over the back, Fig. 51, holding the plate in a sloping position, the vice up. This last process produces a stronger and harder surface than could be obtained if the plate were left gradually to cool. Now place the plate face downwards, supported on one side by the screw of the vice, Fig. 52. Clean the

FIG. 51.

FIG. 52.

smoke from the back, and let it remain until quite cold. Some difficulty may be found in laying the first ground with success, but with a little practice this is surmounted.

Transferring.-In the absence of an etching board, place the copper plate on a thick piece of brown paper larger than the plate; make two ribs of the same paper, doubled four or more times, and about an inch wide; place them at each end of the plate on the brown paper, and fasten them with sealing wax; these ribs serve as shoulders for the rest to lay on which will prevent the hand from touching the work. Now cut the tracing paper to the size of the plate, having ruled the margin line if one is required. the tracing reversed; that is, with the pencil side to the plate. Fix it with pieces of soft wax round the border, leaving open the bottom to admit the transfer paper, which introduce with the chalk side next to the plate; the upper

Place