THE MANUFACTURE OF CLAY-DUST TILES HAVING SURFACES IN RELIEF OR INTAGLIO.
Fig. 207 is a plan of a tile with an intaglio figure thereon, representing its use as a mould. Fig. 208 is a plan of a tile with a figure in relief thereon, also representing its use as a mould. Fig. 209 is a cross-section, illustrating the manner of their use. Mr. Low, the inventor of this process, uses a plastic material, like paraffine, and places it in the tile-frame of the tile-compressing machine, and subjects it to pressure, thus pro ducing a flat thin plastic plate of about the thickness of a tile ; or he takes a quantity of clay-dust and similarly compresses it, and saturates this dust with paraffine. The upwardly presenting surface of this plate is then plentifully sprinkled with pulverized plumbago, which is compressed into the sur face of the plate.
The compressed plate may now be engraved with any de sired pattern, care being taken to cover it with black-lead powder, brushed on with naphtha, or any other solvent of paraffine as a vehicle, or dusted on to a slightly-warmed sur face, or stippled on with a stippling-brush. The parts denuded by engraving can be used as an electrotype mould to make a reverse, and the electrotype used as a matrix to make an ob verse. These electrotypes, well backed, as when used for printing, and set in steel or other strong boxes to prevent crush of the backing, will serve as dies for making the intaglios and reliefs for stamping tile in dry-clay dust.
In case high reliefs are desired, the paraffine (or better, the clay and paraffine) plate may be carved, as desired, carefully avoiding under-cutting, and then covered with its plumbago surface, by the naphtha process or stippling, and electrotyped and used as the die.
When high reliefs, which it is desirable to undercut, are to be made, the mould is made so that the compressed clay will draw, and the main part of the design being thus formed, the modeler carves the undercutting by hand, the clay being suf ficiently tenacious when compressed to allow this, and the finished tile, partly hand-made and partly machine-made, is then fired.
For obtaining textures, low reliefs, or intaglios of natural ob jects, and the like, the inventor may, if he desires, use the paraffine plate made, as has been described above, with plum bago surface, for electrotyping ; but, instead of engraving it, he forms an impression in its black-leaded surface by the objects he wishes to represent, in the manner hereafter described for unleaded paraffine or clay-dust. It is preferable, however, as
it gives great variety in design with slight expense, to adopt the following manipulation : Having formed the compressed plate, as already described, raise in the tile-frame of the tile machine the lower platen till the upper surface of the com pressed plate is conveniently near the top of the frame, and compose upon the surface, by laying thereon bits of woven stuff, lace, pieces of embossed paper, leather, or other fabric, leaves, grasses, flowers, or other objects having suitable textures and outlines, such a design as will be attractive ; then lower the platen to place, and bring down the plunger with strong com pression upon the objects. By this means they are indented in outline and texture in the plastic or clay-dust surface, even overlays being represented with an accuracy absolutely true to nature, and always intaglio.
As already said, this intaglio may be used as a mould for electrotypes, when properly made, by the use of pulverized plumbago as a surfacing agent ; but the inventor usually takes this matrix so made, and places over it a diaphragm of thin, tough material—a rubber film will serve, and many other ma terials ; but the best and cheapest is the thin Japanese paper, of uniform texture and great toughness, such as appears in the Japanese handkerchiefs and napkins, so called. This dia phragm must exactly cover the surface of the intaglio. Upon it is next laid the dust of surface and body-clay of the tile to be embossed, which is subjected to compression in the ordinary way, and thereupon, on raising the plunger and platen, the in taglio and relief may be separated, the diaphragm peeled by aid of a sharp tool to start it from the die, usually the relief, to which it generally, if not always, adheres, and the intaglio will usually, with proper care in handling, be found perfectly unin jured during several hundred impressions.