By mixing various metallic oxides with the boracic acid, designs in colour may be produced. (Dode..)

The surface to be ornamented is covered with a sensitive varnish, and the design, being made transparent, is laid on the varnish, and the light is allowed to act on the sensitive film through the picture. After sufficient exposure, the picture is removed, and colours are applied in the following manner:- The finely - pulverized pigments or enamels are taken up (in a dry state) by a brush applied to the parts where they are required, which can be clearly distinguished in the layer of varnish on the article. The colours or enamels adhere more or less according to the degree to which the adhesiveness of the varnish has been affected; that is to say, according to lights and shades in the design to be reproduced, or according to whether the varnish has hardened more or less. The varnish may be composed of yellow gelatine, gum-tragacanth, and quince - seeds mixed with rain - water, and chrome salts, such as potash bichromate, added, to sensitize it. The composition of the varnish for normal conditions may be -

If the atmosphere is very dry, the quince - seeds may be replaced by sugar, glucose, or honey; or these may be used in addition. The proportions are merely approximate, as the exact preparation will have to be varied according to the conditions of the light, the degree of dryness of the air, and other conditions; but practice will readily suggest what is requisite to those skilled in kindred processes. When the oxides have been applied, they are protected by a coat of thick turpentine, such as is known in France as terebenthine grasse, attenuated, if required, by common turpentine, and the other superfluous parts of the varnish removed by immersion for 24 hours (more or less) in water acidulated with vinegar or other acid, say pure acetic or hydrochloric The strength of the bath (viz. the proportion of acid therein) may be varied within reasonable limits, and determines the length of time which the immersion has to last. The more acid in the bath, the shorter the immersion; the weaker the bath, the longer the immersion has to be. The object is then dried, touched up, and further coloured with metallic oxides, if desired, and fired in a kiln.

Copies of works of art and the like, such as portraits on glass (whether seen by transparency or by reflection), and either fired or not, whether they are drawn from nature or a copy of photographs, or of other design, are with advantage produced by making 2 or more facsimile copies as above described, the copies being exactly fitted one over the other; 2 copies, whereof one at least is transparent, are sufficient in most cases. Upon one of these, the enamels, metallic oxides, or other suitable colours, may be applied, or it may be touched up after the colours are fired; the second copy is placed over the coloured one, so that all details and contours register exactly in both pictures, and consequently appear as a single image to the eye. The 2 copies are united, especially, if on glass, fired with a flux applied at the edges, so that the 2, being fused together, form a single piece; this may also, when practicable, be effected by the firing which fixes the colours. The manner of uniting the plates by the interposition and fusion of a flux is the one which is preferable.

Where a simple ornamental design, or ornamented surface without figures, is desired, it can be obtained upon glass and other articles by applying a varnish composed of asphaltum, pitch, or an equivalent material, dissolved in spirits of turpentine, to which sulphuric ether is added. The plate is then dried, and the design is applied; the plate is next treated with fluoric acid and water, mixed in suitable proportions, then washed in water, and the varnish is removed, as will be readily understood. This manner of proceeding produces plates which have a "frosted" or "crackled " appearance; that is to say, they appear as if covered by numerous vein-like, grooves or marks. The varnish for this purpose may consist of.

These proportions may vary considerably, and according to their variation will produce a different design. The sulphuric ether may be replaced by light naphtha or by benzoline. The component parts of the varnish do not enter into chemical combination, but merely become mechanically mixed. The mixture is applied to the article by means of a brush or a pad, similarly to " stippling." By this means, the nonvolatile fatty component parts of the varnish adhere in flakes or patches to the article, and protect it, and the fluoric acid attacks only the parts not so protected, and thereby the design is produced. (Micciullo.)

The exceedingly delicate coloured photographs on glass, which have come into fashion somewhat of late, are produced by fixing a paper photograph upon a cushion - shaped glass with transparent cement, and when it is dry, rubbing away two - thirds of the thickness of the photograph by sandpaper. The thin film left is then rendered transparent by soaking in melted paraffin wax, after which transparent colours are applied, which appear softened down when looked at from the front. The background and heavier portions of the picture are then painted in body colour upon the face of another cushion - shaped piece of glass, which is afterwards fixed behind the first one. An improvement in this process has just been made by Mrs. Nelson Decker, daughter of the late C. F. Varley, F.R.S. She has dis-covered that the second sheet of glass may be abolished, a better artistic effect be produced, and the picture rendered more permanent, by protecting it from the action of the air and deleterious gases by wholly embedding in paraffin. She does this by quickly dipping the photograph into paraffin a second time after the transparent colours have been applied, and painting the heavier colours upon the back of this second coat.

A third layer of paraffin is then applied, and the background is painted upon that; this third coat may be finally protected by yet another layer of paraffin. Some practice is necessary to acquire the "knack" of doing this efficiently. It must be done rapidly enough not to re - melt previous layers, and the plate must, after each dipping, be quickly tilted on end in such a manner that the paraffin does not run into ridges and thickened lines, but forms an even coating. (Engineer.)