Thus we see that grease anyhow applied to the stone will yield impressions, but that the character of the impression depends, 1st, on the quality of the grease ; 2dly, on of grease; and idly, on the manner in which the grease is ap ied. A. illustration., we refer to the modes already enumerated, in which the Application of the chemical preparation in the shape of a solid chalk, of laid ink, and of pure oil, directly applied to the stone, have been pointed out, and the effects arising from each explained. It is the grease therefore which prints, and the lampblack introduced into the lithographic materials is of no other use than to enable the artist to judge of the quantity of grease imparted to the stone. That it does not in the slightest degree contribute to produce greater darkness in the impression, is proved by a very curious phenomenon. The design may be (and often is, in the progress of printing) washer) out with turpentine, so as to become quite Invisible ; and a looker-on, unacquainted with the subject, would suppose the work to be completely destroyed ; but it is the black only which has disappeared; the grease remains, and on being rolled in again. the drawing re-appeara uninjured.
The variation in the quality of the tints, arising from the mode in which the grease is applied, may be further illustrated by reference to the dabber, which is an instrument by which tints of exceeding delicacy may be produced. It is made of very smooth leather, being somewhat round on its face, and stuffed with cotton wool. On the face of the dabber a lithographic prepaention, softer than the chalk, is evenly and thinly applied with a hard brush, and afterwards imparted to the stone by repeated blows with the instrument. The dabber was formerly much in use, particularly for delicate skies ; but as lithography has been longer cultivated among us, our artists have acquired greater manual dexterity, and produce tints of the greatest delicacy with the hand alone, which have the recommendation of standing better than these produced with the dabber. Another mode of applying the greasy material, which was introduced some years back, and was found in skilful hands to produce very effective results, was by means of a stump, as in crayon drawing [Citaroes], to which the process is very similar. with a modification of the ink already described, drawings were made by washing, or laying in tints, with brushes (or camel-hair pencils) much as drawings are ordinarily made with India ink or sepia. By both these means almost perfect facsimiles of artists' sketches may be produced : indeed, as is evident, lithography 'admits of any mode of manipulation which may suit the habits, taste, or style of tho artist, so that it be consistent with the main principle of the art.
The printing from two or more stones, which was practised with indifferent success almost in the earliest stages of lithography by Senefeldcr and others, has within the last few years been very exten sively practised. In this style, when all that is desired is to imitate a drawing made on tinted paper, with the high lights laid on with white, the drawing is first made in the usual way, with chalk on a grained stone, but more slight, the sky and other delicate tints being omitted, and these are superadded from the "tint stone." The tint is executed with facility by the printer on another atone (polished), with a modified preparation of chemical ink„and thus much labour is saved to the artist. The extreme lights are then scraped out on this tint stone, and the printer superadds the impressions from it to those already taken from the drawing on the other stone ; of course taking great care that the two fit well, or "register," as it is technically called.
But the most important application of this process is in the pro duction of copies of coloured drawings and paintings; a process known as chrome-lithography. The object here being to produce as nearly as possible facsimiles in colour, touch, and texture, as well as in drawing and light and shadow, of pictures from the pencils of painters of the highest standing, it has been found neccesary to employ a large number of stones, in order to produce the almost infinite varieties of tints which are found united in a single picture ; every stone giving a sepa rate impression in its own particular colour or tint. The mode of pro cedure is somewhat as follows. First, an outline of the entire eubject is made by means of transfer paper, or otherwise, on a stone which is called the outline or key-stone of the work. This stone yields impres. !ions which are transferred as guides to all the other stones. On a second and third stone which serve an the basis of the print the general effect of the drawing is washed in,and from these are printed what ma be called the chiaroscuro, in a faint tint of sepia and of a neutmi colour or gray : corresponding in fact very nearly to the neutral or dead-colouring of a water-colour drawing in the method adopted by the early water-colour painters. The stones which follow are each
charged with a particular colour or tint, and each leaves its impression on only a particular portion of the print : one stone printing only the parts which are intended to be yellow or a modification of yellow ; another red, another blue, and so on. Other stones charged in parts with grays or secondary colours serve to blend and harmonise the crude colours ; others follow which modify these, and finally, one gives the sharp dark touches, and is usually followed by another which supplies a sort of glaze or finishing wash, and subdues and hen:mulles the whole. Of course, we hare only broadly indicated the general method. It will be understood that the sequence of the colours in the printing; the special quality and strength to be given to each particular tint; the effect to be produced by their superposition, and many other particulars, have all to be taken into account in planniug the arrange ment of the colours on the stones ; since a sequence in some respects different, and an entirely different modification of colours, have to be employed for the works of most artists; and it happens that much of the colour on each of the earlier stones is covered by that of succeeding stones, and that thus only can the broken tints of the original be imitated. It is in fact only by watching the progress of a print through all its stages that any clear idea can be obtained of the beauty and accuracy of the whole process, of the prevision that must be exercised, and of the skill, care, and taste required at every step to carry it to a successful termination. For some of the more elaborate prints—one or two after Turner, for instance—from thirty to forty stones have been required to a finished print. And in order to produce this print, it must be borne in mind that each sheet of paper has to be passed as many times through the press as there are stones, since each stone imprints upon it only its own particular section of the work. Of course, in proportion to the increase in the number of the stones, does the difficulty increase of making the work upon each fall exactly upon its proper place in the general design ; for if any one were misplaced only the fiftieth of an inch, the drawing and colour of the whole would be disturbed. Hence it is found necessary to arrange the register, or adjustment of the stones, with the utmost care and precision ; and to exercise the most careful supervision in the printing (which is entirely a hand process), since the sheet of paper expands considerably in passing through the press, and has to be dried and re-damped before it can be passed through again. But practically this is all accomplished with seeming ease, and a large and most complex subject will be found, when the last stage has been reached, to bear the most minute scrutiny ; and the result, even when the copy is placed alongside the original, will surprise and delight equally those who have followed the work through its several steps, and those who may only examine the completed work.
Transfer lithography has been applied in other ways than the one already explained : indeed it would be difficult to fix limits to its capabilities, improvable as they may be in the hands of able chemists. Among the transfer modes, that of printing copper-plate engravings from stone is worthy of notice. An impression is taken on unsized paper from the copper-plate, and without delay transferred, by passing through a press, to a polished stone ; it is then acidulated, and the printing proceeds in the usual way. In some kind of work the im pressions thus obtained are scarcely distinguishable from those printed direct from the copper. The advantage which this application of. lithography holds out is most apparent where economy or great despatch are important. These objects are both obtained by trans ferring impressions to several stones, or several impressions to one stone if the design be small, when the numbers can be multiplied with great rapidity, and without the original engraving being at all worn, Plates of zinc are for some purposes much used as substitutes for the German stones, in chemical printing, and the practice is then called Zineography ; but excepting the difference of the material on which the work is performed, it is precisely the same art as lithography. Zinc plates have the advantages of greater portability, and of being liable to break from the pressure in printing.