Painting by Immersion and by Compressed Air: A Practical Handbook

by Arthur Seymour Jennings

A very ingeniously constructed, although simple, mask which is suitable for many purposes, but particularly for motor and carriage lamps, has been patented by Mr. Walter William Hart, of the firm of Matthew J. Hart & Sons, Great Barr Street, Birmingham, and others. By this invention means are provided for applying the mask to a plain surface so that it may be immovably held without causing injury to the surface. The mask, too, has the advantage that it can be placed in position with extreme rapidity. By this invention the mask is fastened in position by a suction pad, preferably made of indiarubber, which, when pressed on to the surface to be covered, adheres thereto by the pressure of the atmosphere. In Fig. 93 is shown an inner face view and a sectional elevation of the device. The mask (a) is adapted to have an axial movement in relation to the suction pad (b) so that when such pad has been fixed in position the mask may be pressed close upon the surface it is required to protect. This suction pad (b) is of a conical formation, and is secured to the end of the plunger (c) which passes rearwardly through a hole (d) in the back of the mask, and through a tubular extension (e) passing rearwardly from the back of the mask. The rear end of the plunger has a hole therein, which hole is screw threaded, and to such end a cap (f) is secured. A stud (f) on the interior of the flat end of the cap screwing into the said tapped hole, and the cylindrical portion (f2) of the cap slidingly fitting over the tubular extension (e) on the mask. A spiral spring (g) surrounds the plunger, one end bearing on a shoulder (h) at the rear of the mask and the other end bearing against the cap (f). To fasten the mask, the same is placed in position over the part to be covered and the cap (f) is pressed down, thus pressing the suction pad (b) upon the surface of the article, to which it adheres. A mask constructed according to this invention is capable of a great variety of applications, one of which is in connection with lamps. That shown in the illustration is intended for this purpose.

It will be clear that the shape, however, can be varied according to the article to be painted by spraying; for example, it may be used with advantage for decorative purposes.

MAKING STENCILS.

When it is decided to spray through stencils, it is usual to employ thin copper plates for the purpose, although in wallpaper decoration very heavy copper stencils are used, because, these being held horizontally, the weight increases the stiffness of them, while it prevents them shifting while in use. In ordinary work, however, where a stencil must be used vertically, the lighter stencil will be most useful. If paper is used, the best material is Japanese vellum, which is manufactured from a special fibre and possesses the advantage of being easy to cut and makes remarkably durable stencils. It is imported from Japan by Jas. Spicer & Sons, Ltd., 15, Upper Thames Street, London, E.C. Manilla paper may be had from the same firm, and answers also very well. For some styles of work, lead foil gives good results. Messrs. Locke, Lancaster, and W. W. and R. Johnstone & Co., Ltd., 94, Gracechurch Street, E.C., supply a material which they call "Four-ounce stencil metal," which weighs 4 ounces to the square foot, is made in sheets 6ft. by 2ft. 6in., and in smaller sizes, and costs 2s. per lb. It can be easily cut with a stencil knife, and is most suitable for work on horizontal surfaces. Another paper which may be used is ordinary Whatman's paper. The usual method of cutting is to use a very sharp knife, such as a shoemaker uses, and to cut on a sheet of glass. If any variety of paper is employed, it will be necessary to apply two coats of shellac varnish, ordinarily called "Patent Knotting." This protects the surface of the paper from being worn away by the action of the brush. Some stencil cutters prefer boiled oil for the purpose.

Zinc stencils are sometimes employed. These may be made as follows: The thinnest sheets of zinc are employed for the purpose, and upon this is painted the letters or design to form the stencil. The whole of the zinc which is not to be cut out, or rather, by this process, eaten out by acid, must be protected by means of a varnish made as follows: Take one pint of best asphaltum varnish, two ounces of beeswax and half-an-ounce of rosin and four ounces of Venice turpentine. Melt the beeswax and rosin in the Venice turpentine, and while warm add the asphaltum varnish, mixing thoroughly together. Paint this on the back of the zinc plate and on all parts that are to be protected. Form a dam or little wall made of 6 parts of beeswax and one part of tallow melted together and allow to cool. This is intended to confine the acid to the parts required to be eaten out. Nitric acid is used for the purpose mixed with three parts of water. This is poured on the space inside the dam and allowed to remain on for from 24 to 48 hours, when it will be found to have eaten away the zinc on the parts unprotected. Further information concerning stencils will be found in the book entitled "Stencils and Stencilling," by A. L. Duthie, published by the Trade Papers Publishing Co., Ltd., 365, Birkbeck Bank Chambers, High Holborn, London, W.C., price 3s. 3d.

REQUIREMENTS OF SPECIAL TRADES.

The following hints are given of the requirements of a few special trades:—

Piece Work.

In very many cases where articles are painted by means of compressed air it will be found quite practicable to have the work done by piece work. The exact time taken to spray any particular article can, after a very little practice, be determined quite accurately. In fixing the price to be paid for the work an allowance must, of course, be made for the time taken in bringing the piece to the spraying cabinet and placing it ready to be taken away by the boys or labourers. It is in this detail that speed may be increased so materially. The actual time of spraying to a great extent regulates itself, but if care is not taken considerable waste of time will be occasioned in getting articles ready and taking them away, and a satisfactory arrangement of piece work to both employer and employee will remove this waste of time and will prove more beneficial than day work.

Bookbinding.