Printing.

WHEN the intention is to print from the stone, it is placed upon the platten or bed of the press, and a proper sized scraper for the printing is adjusted to the surface of the stone. Rain water is then sprinkled over the gum on the stone, which being dissolved gradually, and a wet sponge passed lightly over it all, the printer works the ink, which is on the colour-table placed beside him, with the roller in all directions, until it is equally and thinly spread all over the roller. The roller is then passed over the whole stone, care being taken that the whole drawing receives a due portion of the ink, and this must be done by giving the roller an equal motion and pressure, which will of course require to be increased, if it is perceived that the drawing does not receive the ink readily.

When the drawing is first used, it will not receive the ink so readily as it will afterwards do; and it is frequently necessary to wet the stone, and roll it several times before it will take the ink easily. When the drawing once takes the ink readily, care must be taken not to wet the stone too much. Indeed, the less dampness now the better, provided there is sufficient to prevent the stone from taking the ink where there is no drawing.

After the drawing is thus rolled in, the sheet of paper is placed on the stone, and the impression taken in the manner described in the account of the press. When, after the impression, the paper is taken up, the stone appears dry, the moisture having been imbibed by the paper. It must, therefore, again be wetted with a sponge, and again rolled in with ink, the roller having been well worked on the colour-table before being applied.

During the printing, some gum must always remain on the stone, although it will not be visible, otherwise the ink will be received on the stone, as well as on the drawing, and the drawing spoiled. So that if by too much wetting, or by rubbing too hard with the sponge, the gum is entirely removed, some fresh gum-water must be laid on. If the stone has in the first instance been laid by with too small a quantity of gum, and the ink stains the stone on being first applied to it, gum-water must be used to damp the stone instead of pure water.——— Sometimes, however, this may arise from the printing ink being too thin, as will afterwards appear. If some spots on the stone take the printing ink, notwithstanding the above precautions, some strong acid must be applied to them with a brush, and after this is washed off, a little gum-water is dropped on the place. A steel point is here frequently necessary to take off the spots of ink.

The edges of the stone are very apt to soil, and generally require to be washed with an old sponge or rag after the rolling in. They must also frequently have an application of acid and gum, and sometimes must be rubbed with pumice stone.

If an ink is too thin, and formed of a varnish not sufficiently burned, it will soil the stone, notwithstanding the proper precautions are taken of wetting the stone, and preparing it properly with acid and gum; and

if on the other hand the ink is too thick, it will tear the lighter tints of the chalk from the stone, and thus destroy the drawing.

The consideration of these circumstances leads at once to the

Principles of the Printing.

These accidents arise at the extreme points of the scale at which the printing inks can be used, for

it is evident, that the only inks which can be employed are those which are between these points; that is, thicker than that which soils the stone, and at the same time thinner than that which takes up the drawing. Lithographers are sometimes unable to print in very hot weather, the reason of which may be deduced from the above. Any increase of temperature will diminish the consistency of the printing ink; the stone will therefore soil with an ink which could be safely used at a lower temperature; hence a stiffer ink must be used. Now, if the temperature should increase

SO

much that the stone will soil with any ink at all less thick than that which will take up the drawing, it is evident that the printing must cease till a cooler temperature can be obtained; for as the drawing chalk is affected equally with the printing ink, the same ink will tear up the drawing at the different degrees of temperature. This, though it sometimes occurs, is a rare case; but it shows that it is desirable to draw with a chalk or ink of less fatness in summer than in winter; and also, that if the printing room is in winter artificially heated, pains should be taken to regulate the heat as equally as possible.

Other difficulties in Printing, not referable to the above general principle.

If the pressure of the scraper is too weak, the ink will not be given off to the paper in the impression, although the drawing has been properly charged with it. Defects

will also appear from the scraper being notched, or not correctly adjusted, or from any unevenness in the leather or paper.

After printing a considerable number of impressions, it sometimes happens that the draw

ing takes the ink in dark spots in different parts. This arises from the printing ink becoming to strongly united with the chalk or ink of the drawing, and if the printing is continued the drawing will be spoiled. The reason of this is easily ascertained. The printing ink readily unites with the drawing, and being of a thinner consistency, it will, by repeated applications, accumulate on the lines of the drawing, soften them and make them spread. In this case it is necessary to stop the printing, and let the stone rest for a day or two, for the drawing to recover its proper degree of hardness. If the drawing should run smutty from any of the causes before enumerated, the following

Mixture for cleaning the Drawing while Printing

The

must be used. Take equal parts of water, spirits of turpentine, and oil of olives, and shake them well together in a glass vial, until the mixture froths, wet the stone, and throw this froth upon it, and rub it gently with a soft sponge. printing ink will be dissolved, and the whole drawing also will disappear, though on a close examination, it can be distinguished in faint white lines. On rolling in again with printing ink, the drawing will gradually reappear as clear as at

first.

Bleached Paper unfit for Lithographic Printing.

Accidents sometimes occur in the printing, from the qualities of the paper. If the paper has been made from rags which have been bleached with oxymuriatic acid, the drawing will be incurably spoiled after thirty impressions. Chinese paper has sometimes a strong taste of alum; this is so fatal as sometimes to spoil the

drawing after the first impression. When the stone is to be laid by after printing, in order that it may be used again at a future period, the drawing must be rolled in with a

Preserving Ink,

as the printing inks would, when dry, become so hard, that the drawing would not take fresh printing ink freely. The following is the composition of the preserving ink:-Two parts of thick varnish of linseed oil, four parts of tallow, one part of Venetian turpentine, and one part of wax. These must be melted together, then four parts of lamp black, very carefully and gradually mixed with it, and it must be preserved for use in a close tin box.

Very good effects are produced in lithographic prints, by

Printing from two or more stones with different coloured inks. This is managed by preparing a composition of two parts of wax, one of soap and a little vermillion. Melt them in a sauce pan, and cast them into sticks. This must be rubbed up with a little water, to the thickness of cream, and applied to the sur

face of a polished stone. An imimpression is taken in the common way from a drawing, and applied to a stone, prepared in this manner, and passed through the press, taking care to mark, by means of this impression, two points in the margin corresponding on each of the stones. The artist having thus on the second stone, an impression from the first drawing to guide him, scrapes away the parts which he wishes to remain white in the finished impression. The stone must now be etched with acid, stronger than the common etching water, having one part of acid to twenty of water. The whole is then washed off with turpentine. This plan is generally used to print a middle tint from the second stone. The black impression being given from the first stone, a flat transparent brownish tint is given from the second, and the white lights are where the paper is left untouched. The dots are necessary to regulate the placing of the paper on the corresponding parts of the two stones. The paper for lithographic printing should not be so damp as for copperplate printing.

As we did in our article on Bronzing, we shall, first, give directions for making the lacker, and afterwards proceed to describe the manner of using it. We have seen many receipts for making lackers, but the two following are the cheapest, and answer all the purposes necessary for brass goods; particularly as they can be used when necessary, along with any of the colouring liquids, directions for making which we shall also give. We shall first give a receipt for making

Common Lacker for Brass. And in order to prepare this properly, it is necessary to select the best seed lac which can be procured, which must be washed in water, and then dried, and beat in a mortar to a coarse powder. Dissolve six ounces of this powder in two English pints of spirit of wine. They must be both put into a tin or glass bottle, which will hold nearly double the quantity meant to be prepared. Shake the bottle well, and then place it in a warm situation, near a fire or stove, which

use.

will hasten the solution. Shake the mixture occasionally, say every three or four hours, for the first and second day; allow it to stand still for twenty-four hours more, when the insoluble portion of the lac will have fallen to the bottom, then gently pour off the pure part into a clean bottle, and it is fit for This lacker will answer for all kinds of common brass work, tin plate, block tin, &c. It has a redish yellow colour, which may be heightened at pleasure by laying on two or more coatings. Its colour likewise be easily varied by may the use of the colouring solution to be afterwards described. When this lacker is used as a varnish to bronzed work, it gives it a brownish coloured ground. The only other lacker we mean to describe, is a

Fine Pale Lacker,

which is prepared with shell lac, instead of seed lac, and with highly rectified spirit of wine. The most transparent part of the shell lac must be selected, and it must be washed in clean water. It is then allowed to dry, and afterwards pounded into a coarse powder. Of which let ten ounces be taken, and mixed with two English pints of highly concentrated spirit of wine or alcohol. The mixture is then put into a glass bottle, capable of holding, as in the former case, about twice the quantity wished to be made. The bottle must then be stopped up, and placed in a warm situation, and shaken, as in the former instance. When the solution is completed, the clear part is to be gently poured off, and the remainder filtered through a sheet of strong blotting paper. This must then be added to the portion first poured off, and the residium which remains in the paper is then to be thrown away.

Both lackers must be preserved in

a close bottle; and if properly made, and kept from the air, either of them will keep for years, and still be as good as ever. The last described lacker, when used without colouring, is scarcely seen upon varnished or dipped brass, but it will preserve it for many years, and prevent it tarnishing. We shall now describe how to make the best

Colouring mixtures for strengthening the Colour of either of the preceding Lackers.

1. Infuse one and a half ounce of turmeric root, and two drachms of gum tragacanth, in an English pint of spirit of wine, by keeping it in a warm place and shaking it frequently for two or three days. This infusion may be made stronger or weaker by using a little more or less of the gum.

2. The same quantity of turmeric root and spirit of wine, without the gum, gives a fine light yellow.

3. Infuse one ounce and a half of saffron in the same quantity of spirit of wine, and it will produce a dark redish colour; add equal parts of this and the 2d together, and it will give a strong bright yellow.

4. Dissolve one-fourth of an ounce of sap green in about half a pint of spirit of wine; add a few drops to any of the above, before mixing them with the lacker, and a bright greenish yellow will be obtained.

5. Dissolve half an ounce of gambouge, in about three-fourths of an English pint of spirit of wine, and it will produce a fine bright yellow.

6. Dissolve half an ounce of gambouge and half an ounce of gum tragacanth, in two pints of spirit of wine, and the mixture will give a fine gold colour.

When it is wished to use any of these colouring mixtures, pour out

a little of the lacker into a cup or lacker dish, made for the purpose, and add the colour by a few drops at a time, until you have attained the shade which is wished. When

a great quantity of work must be done at the same time, or at different times, of the same colour, the quantities of the lacker and colouring mixture ought to be carefully measured or weighed, as a great difference of shade will be the consequence of a very small difference in the quantity either of the lacker or the mixture.

We shall now proceed to describe

The Method or Art of Lackering, which is indeed very simple. The work being finished, must be made perfectly dry, and entirely freed from grease. It must then be heat

ed on a piece of hot cast iron, or a very clear fire, until it can scarcely be held in the hand. The lacker must then be laid on in very thin, and equal coatings, from two to five or six in number, according to the colour which it is wished the work should have: heating it always be

tween the coatings, to harden the lacker, and make it adhere to the metal. Great care must be taken that no dust is flying at the time, as that would make the work have a rough or dirty appearance. The brush used for lackering, is a flat thin brush, made of camel's hair; it may be about an inch or threefourths of an inch broad, and about one-eighth of an inch thick, and can be procured in the colour shops.

If at any time a part of the work is spoiled in lackering, whatever lacker may have been put on must be completely removed before any attempt is made to mend it; and this is done by boiling the work in a solution of pot-ashes in waterabout one ounce of pot-ash to a Scotch pint of water. The work must be put among the boiling liquid, and

in a few seconds the lacker will be disengaged. It must then be washed in clean water, and dryed in warm saw dust, and it is then ready to be again lackered. In this manner, likewise, the lacker must be removed from old brass work, before any attempt be made to clean it, or to lacker it anew.

ON THE LOSS OF POWER
THE

To the Editors of the GLASGOW MECHANICS' MAGAZINE. GENTLEMEN,-As there appears to be a fallacy in your Correspondent A. B.'s reasoning on the loss of power by the crank, which renders entirely useless his very ingenious invention, I hope you will not refuse to undeceive your readers.

A. B. will readily perceive that the simplest and most efficacious application of his invention would be, to have his wheels, which are to supersede the use of the crank, placed immediately above the piston rod, and to have a common rack attached to the piston rod, at each side of them. It is singular that this very contrivance was adopted, but not extensively applied, twenty years ago, by