Part 7 (1/2)
[Ill.u.s.tration: FIG. 28.--Convenient method of stacking decorated metal plates to distribute their weights and prevent injury.]
Take, for instance, a course of eight printings, each one absolutely necessary to the design, and each one to be dried by stoving. It is only reasonable to suppose that the first and second printings will be seriously affected by the subsequent stovings. They will undoubtedly harden to such an extent as to render the super-position of other colours a difficult matter, and their purity of tone will most probably be affected. According to the same line of reasoning, some sheets would be more affected by the heat than others, owing to their position in the racks, the heat of stoves being greatest near the top.
Air-drying can only be accomplished by adding to the printing ink a proportion of some suitable drier. (_See_ Transfer Printing, p. 71.) Naturally, it requires a much longer time, but it is equally effective, much less troublesome, and generally more satisfactory.
CHAPTER XIV
TIN-PLATE DECORATION
Suitable Designs--A Variety of Effects--Gold Lacquer-- Super-position of Colours--Embossed Effects--Embossing Plates--Lacquers.
It is usually and rightly supposed that the most effective results in Tin-plate Decoration are produced from designs which are lithographed for that specific purpose.
Designs which are specially arranged for Paper Printing can be used so long as the effect produced by the transposition from right to left does not affect its application, or render the same impossible. This, of course, applies more particularly to designs in which lettering appears, but at the same time it may affect designs of an essentially pictorial character in an equally important manner; for it must be remembered that a drawing for Tin-plate Printing must appear on the lithographic stone exactly as it is impressed on the metal, and not, as in Paper Printing, reversed from right to left. This naturally simplifies the drawing on stone, and to some extent enables the draughtsman to dispense with the reversing mirror when copying.
The primary object of this short chapter will be to point out some of the characteristic features of Tin-plate Decoration, so that such methods as are usually adopted by the artist and the printer may be modified or amplified to meet any peculiar requirements of work in hand.
A greater variety of effects can be attained on the polished metal plate than it is at all possible to produce on paper.
A gold effect, the result of lacquer printing, is especially striking.
In a similar manner an excellent translucent l.u.s.tre can be imparted to almost any colour by taking away the white opaque ground, and thereby producing a peculiar semi-transparency which is both pleasing and effective. Lacquer printed over _white_ produces a _buff_ colour, which can be used as a second yellow or to form the base of a flesh. The colour of the lacquer is softer and less obtrusive when printed under instead of above the white. The super-position of colour generally, as described in Chap. XII. page 70, is peculiar to tin-plate printing, and suggests the advisability, if not the necessity, of a special design.
The advantages of such super-position are obvious and substantial. Under ordinary commercial conditions it is almost impossible in tin printing to obtain the same intensity of tones in the printed colours as in paper printing. Some such strengthener as the super-position of suitable colours is therefore necessary. The work of the lithographic draughtsman is in this respect of a somewhat unusual character; but a little intelligent consideration will render its execution on these lines comparatively easy and satisfactory.
As already stated, yellows can be accentuated by a super-position of lacquer, and in the same manner blues and greys add intensity to black.
Red can be strengthened by a foundation of lacquer, also flesh and yellow, either singly or in combination. The drawing of lacquer and white formes should receive the most careful attention. They should fit each other accurately, even to the most minute details; for the slightest overlapping will be revealed by the presence of a very a.s.sertive buff colour, while any deficiency in combination will leave a not less striking margin of bright tin exposed.
In some instances it might be an advantage to transfer one forme from _black_ to _white_ to produce the opposite colour, and thus ensure perfect register.
In decorative designs particularly, tin-plate printing suggests almost unlimited possibilities for brilliant effects, and in this respect it offers fair lat.i.tude for individual originality and manipulative skill.
In the production of show tablets especially, considerable attention has been given to embossing, in order to suggest and represent relief.
Though not actually produced by the artist, this is in effect part of the scheme or plan of his design, and will consequently influence his work to some extent. For simple ornamentation only, metal embossing presents little that is new or novel; but for the production of relief effects in the pictorial elements of a design its application becomes a more important and influential matter. By its aid a flat and otherwise uninteresting subject can be made attractive and vigorous, and for general purposes of effective display its value will be considerably enhanced and its a.s.sertive character emphasised.
Without entering too minutely into matters which affect the lithographic printer in an indirect fas.h.i.+on only, it will yet be useful to him to know how an embossing die is produced which registers accurately with the design to be operated on. A black impression of the outline forme of the design is made on transfer paper similar to that described in Chap.
XII. page 68, and re-transferred, by pressure only, to another sheet of the same paper. The re-transfer is to be the impression required, and this in its turn is re-transferred again to a prepared bra.s.s plate. The only preparation necessary is the levelling and planing of the plate, and, if desired, it can be coated with a thin layer of white paint or enamel. This white ground makes the work easier, by rendering the impression more distinct. With such a guide as this the cutting or engraving is a comparatively simple matter.
The engraved plate is placed in a casting box, and a stereo-metal casting is made from it. A little tr.i.m.m.i.n.g may be necessary for the completion of these two tools, and they will require to be suitably mounted, so that they may be accurately adjusted in the embossing press.
Metal embossing has certain limitations which must be recognised as an essential condition of its effective application.
The plates vary considerably in texture and temper, and the depth and character of relief will, to some extent at least, be controlled by the quality of the metal. Sharp lines and abrupt terminations impose a strain under which many plates split, therefore such features ought to be avoided. Easy, rounded lines, rather than those of the straight furrow description, produce the best results and give least trouble during operations. Where abrupt terminations are quite unavoidable the design should, if possible, be so arranged as to evade the super-position of colour over these parts.
Lacquer, if properly mixed and applied, is probably the toughest pigment used by the tin printer, and is generally suitable for embossed work. It prints an exceedingly thin layer or film on the face of the metal, which under average conditions rarely interferes with the working of the embossing tool.