MECHANICS AND USEFUL AETS. 49 



The metal plates which may be most conveniently impressed by 

 drawings, designs, prints, or photographs, prepared according to this 

 invention, are plates of Britannia metal, copper and German silver; 

 but plates of various other metals and metallic alloys may be simi- 

 larly impressed. 



As a preparation of the plate before engraving or impressing a 

 drawing, design, or photograph upon it, as described, the said plate 

 is usually passed several times through the machine, the surface to 

 be impressed being placed in contact with the surface of the plane 

 or bed of the machine. When a drawing or photograph is executed 

 upon a slab of plate-glass, the metal plate to be engraved or impressed 

 is first passed through the machine upon the usual plane, and after 

 the plate has been passed through the machine several times the plane 

 is removed, and the slab on which the drawing or photograph is exe- 

 cuted is substituted for it. The plate of metal is then passed through 

 the machine in contact with the drawing. 



The patentee gives the following formulas for preparing the paste 

 with the mixtures of hard substances : 



Formula No. 1, 30 parts (by weight) of peroxyd of tin, 2 per- 

 oxyd of manganese, 10 Venetian red, 5 Paris white, 3 rice starch, 8 

 gum arabic, 2 bichromate of ammonia. 



Formula No. 2. 20 parts (by weight) of peroxyd of tin, 10 per- 

 oxyd of manganese, 10 Indian red, 5 Paris white, 3 rice starch, 10 

 gum arabic, 2 bichromate of ammonia. 



Formula No. 3. 15 parts (by weight) of finely-powdered emery, 

 10 Indian red, 10 peroxyd of manganese, 5 Paris white, 5 rice starch, 

 8 gum arabic, 2 bichromate of ammonia. 



When making the drawing, design, or writing upon a sheet of gel- 

 atine, a sufficient quantity of the composition described in formula 

 No. 1 is used, adding as much water as will cause it to flow freely from 

 a pen, or brush, or hair pencil. After being allowed to stand a few 

 minutes to dissolve the gum arabic, the whole is mixed together to 

 about the consistency of ordinary cream. With this are drawn the 

 outlines of the subject, and the other portions in lines and distinctly 

 marked touches to which it may be artistically best adapted. When 

 dry, and after a brief exposure to daylight and the atmosphere, in 

 order that the bichromate of ammonia may act upon the gum arabic 

 and starch, and thus secure the drawing from ready disturbance, the 

 touches are repeated upon such parts of the lines or markings as may 

 not stand out in sufficient relief. For those portions of the lines or 

 markings which it is desirable should be more strongly defined, the 

 composition described in formula No. 2 is used ; and for the parts in 

 which it is intended the lines and markings should be darkest and 

 strongest, the composition described in formula No. 3, mixed with 

 water as before described, is used. 



When a drawing or design is executed on paper, vegetable parch- 

 ment, tracing-cloth, or other suitable fibrous material, the fibrous sub- 

 tance is impressed in the metal plate as well as the drawing or design, 

 and when printed in the manner of copper-plate printing, the impres- 

 sion of the fibre gives a tint all over the drawing or design. To pro- 

 duce a proper effect of light and shadow, the same method is followed 

 as that used in ordinary mezzotinto engraving. If the texture or 

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