INSERTED MOSAIC

This method of mosaic invented by Mons. Aumaitre possesses the advantage of being very durable, owing to the edges of the inlay being secured between the two edges of the incision made in the groundwork. The outline is deeply cut in the groundwork, the incision well opened with the opener and then filled with paste. The inlay is also pasted and the edges inserted in the incision. A wheel or a large modeller is used to press down the edges, and the outline is then gone over with a hot tool.

[Ill.u.s.tration: FIG. 33, FIG. 34.--STICKING INLAY ON MOROCCO GROUND WITH TOOL (FIG. 33) INSTEAD OF ROLLER, TO AVOID CRUSHING THE GRAIN]

[Ill.u.s.tration: 12. SHIELD OF CUT AND EMBOSSED LEATHER, _CUIR BOUILLI_.

ITALIAN, 16TH CENTURY.]

MOSAIC IN RELIEF

The term mosaic is perhaps not very correctly applied to this style of decoration, in which the shape of the design is indented, by pressure, on the damp surface of the groundwork, and filled in with an inlay of leathers thick enough to stand out in relief, and be subsequently carved.

A thin kind of cowhide[8] specially prepared for embossed work is used.

The design is traced upon it in the manner described for carved leather, and a preliminary modelling is executed indicating the outlines and veinings as strongly as possible. The high reliefs may be embossed and lightly stuffed. This done, it is placed upon Bristol board, not less than half the thickness of the leather itself, with a piece of red transfer paper face downwards in between. The whole is firmly fixed upon a drawing board so that nothing can get displaced, and the design is cut out with a stencil-cutter's knife (Fig. 22). If possible, both leather and Bristol board should be cut through at the same time, but should the knife not penetrate the latter sufficiently to cut it through, the outline will have been marked on it by the transfer paper and it may be cut out separately.

The leather and the board must, however, be absolutely identical in shape and very sharply cut. With the die thus formed by the Bristol board, the morocco groundwork is depressed to receive the inlay. It is thoroughly wetted and the water allowed to sink in. The board is then placed in the exact position which the leather inlay is to occupy, and covered with a very thick sheet of blotting-paper to protect the grain of the groundwork from being crushed too much. The whole is well pressed in the copying-press until the die has sufficiently entered into the leather. The leather inlay should then be tried in the hollow thus produced, and trimmed where necessary if it be too large. After pasting it thoroughly, taking care not to omit any small points, it is placed in position on the groundwork and worked into the hollow with a modeller. The work is then placed under boards to dry; a press would flatten the relief too much.

[8] Kip-skins.

When the paste is quite dry and the leather well stuck, the carving may be proceeded with as described in Chapter II.

Very characteristic effects are obtained by colouring leather worked in this manner.

INCRUSTED MOSAIC

The following description of a style of decoration, called by Mons.

Belleville "incrusted mosaic,"[9] is derived from the valuable work of that author, ent.i.tled _Le Cuir dans la Decoration Moderne_.

[9] _Mosaque par Incrustation._

In incrusted mosaic the design is not cut out and applied on the background, but the different pieces of coloured leather forming the design and the leather of the background are placed side by side on the same plane. When the ornament is simple and the background plain, the design is traced on the groundwork, carefully cut out, and used as a pattern for cutting out the piece destined to replace it; when the ornament is to embrace the whole surface, the following method is recommended: The design, drawn on paper and coloured, is fixed on a drawing-board and over it is placed a sheet of transparent paper, or some thin muslin carefully sized and stretched. An exact tracing of the design is made on rather stiff paper, which is coloured or numbered to correspond with the pieces of the different leathers which are to compose the mosaic.

The tracing is then cut out, separated, and the pieces pasted on the corresponding leather, either with the face on the flesh side of the leather, or the back on its surface. In the latter case it is very lightly done, but if pasted on the flesh side it should be done securely, as it will remain permanently. When all these pieces are cut out of the leather they are pasted in their respective places on the design, and the whole put in the press for about ten hours. If the work has been well executed, the lines where the pieces of leather come together will be hardly visible; the next step is to accentuate them and make them regular. This may be done either with a heated wheel giving a smooth even line, which may, if desired, be subsequently gilded, or by pyrogravure. Vigour and character can be imparted to the outline by the use of the latter process, and the darkened colour of the burnt line is made more brilliant by polishing it with an agate burnisher. In either case the tool must be worked accurately with its edge half on each side of the line. The main advantage of the process of incrusted mosaic is that the grain of the leather employed is better displayed than in inlaid mosaic. It is only suitable for work on a large scale.

CHAPTER IV

DYES, PATINES[10] AND GILDING

[10] _Patine_ represents a veneer, or wash of colour, applied on the surface, or in the hollows of leather, to intensify its tone, or to give artificial effects, such as those of verdigris, rust, or antiquity.

Partly owing to its nature, and partly owing to the tanning process, leather is susceptible to the action of the dyes used to colour it in degrees varying according to their composition and penetration. We will not attempt to enumerate all the dyes that may be employed or to describe their composition. Excellent results can be obtained with ready made preparations, and some brief remarks on the subject are all that is necessary for the purpose of this work.

Practical experience alone is a reliable guide in the selection of dyes, as, whatever their base may be, they all vary greatly in use. It may be remarked that there are many aniline dyes which are more durable than vegetable ones, although there are others which merit their reputation for instability. The colour of dyed leather cannot be expected to remain unaffected by constant exposure to direct sunlight, but it should not alter with ordinary use.[11]

[11] See the remarks on Leather for Bookbinding in the Note at the end of this volume.

It is obvious that, in proportion as the colours sink into the leather, they will lose in brilliancy, but on the other hand, this very absorption, which allows colours to be superposed and appear translucent, gives a depth rarely obtainable in materials of less capillarity.

[Ill.u.s.tration: 13. TOP OF CASKET COVERED WITH BROWN CALF, CUT AND SLIGHTLY EMBOSSED. BY FLORENCE HORNBLOWER. MODERN ENGLISH.]

The following notes are intended merely as a general indication of the manner of treating the various substances used in colouring leather.

The substance sold by druggists under the name of pota.s.sium is very violent in its action and would burn the leather as well as the brushes used to apply it. It should only be employed, and that very sparingly, for such purposes as black lettering. Pearl-ash should be used in preference, but also with great caution, or it will not only destroy the surface, but rot the substance of the leather.

Potash is soluble in water to saturation point, that is to say, a given quant.i.ty of water will not dissolve more than a given quant.i.ty of potash.

It is very difficult to measure the exact strength to use; that which is barely sufficient to penetrate and colour a surface artificially made smooth by rolling, will sink in where the leather has been cut or punched and immediately darken it considerably. It is a good plan therefore to experiment on a spare piece of the leather. Potash lye is more easily used in the right proportion, and may be employed for staining very light coloured leather.

Soda has the same effect as potash, except that it is a little less strong; both substances have always been much employed in dyeing skins.

Permanganate of potash is supposed to dye a mouse-grey colour, but it is most uncertain in its action, as it depends entirely on the porosity of the leather. Xanthin and catechol browns are pleasing in appearance, but their effect is less rich than that obtained with potash. They become improved by hard rubbing with encaustic.

Sulphate of iron has a strong and persistent odour and is also somewhat injurious. It is useful, however, and produces a colour varying from a light shade to an intense violet black. When used over potash, a dead black is obtained.

REDS

Alizarin, the colouring principle of madder, which can also be obtained from coal-tar, is employed in many colour combinations and gives a fine durable red. Hydrochloric acid changes it to violet. Carthamine and cochineal also produce good reds; the latter is turned orange by the action of hydrochloric acid.

Hydrochloric acid turns ammoniacal cochineal pink, but merely discolours the red made from archil. Direct extracts of red wood are unaffected by it.

The colouring matter of logwood, extracted by treating the powder obtained from an aqueous decoction of the wood with spirit, is sold as hematoxylin.

Metallic salts convert it to a violet black, salts of tin change it to pink, alkalis to blue, and acids to yellow. Durable pinks are obtained directly from carthamine, the colouring matter of _Carthamus Tinctorius_.

YELLOWS

The base of most fine yellows is picric acid. The chromates of zinc and baryta give very permanent yellows, which are particularly useful in mixing greens.

The vegetable yellows are less durable. They include turmeric, which is especially fugitive, and quercitron; the former is turned red, and the latter brown, by the action of hydrochloric acid.

Orange tints are easily obtained by using red over yellow, first allowing the yellow to dry completely; or they can be bought ready prepared with alizarin. Mandarine and nasturtium tints can also be bought ready prepared, or may be made by a mixture of vegetable colour, such as saffron and arnotto.

[Ill.u.s.tration: 14. EMBOSSED AND PUNCHED BROWN CALF BINDING. _RUBaIYaT OF OMAR KHAYYaM._ DESIGNED BY MARY G. HOUSTON. MODERN ENGLISH.]

BLUES

Good and durable blues are obtained from indigo and alizarin.

GREENS

Greens of every composition are fugitive, especially those sold ready mixed. Better results are obtained by applying yellow and blue one over the other than by the direct application of the colour, but when the range of tints thus afforded is too restricted, recourse must be had to some of the numerous dyes varying in tint from greenish yellow to deep olive.

Successive applications of sulphate of iron and picric yellow will produce the latter colour, and a vegetable green, which, however, is not very durable, is made from buckthorn berries.