RESERVES.

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when the machine is working the parts of the pattern which have been cutout receive the impression, and thus form the reserve parts of the pattern.It is evident that to obtain satisfadtory results the greatest precision must beobserved in applying the cardboard to the pressing cylinder, so that theengraving roller will only press where required. The great advantage of thismode of producing reserves is that, by employing a pressing roller of sufficientdiameter, reserves of large surface can be easily obtained. Under the nameof conversion is designated a certain modification of the shade of any colourproduced on cloth by means of the intervention of some chemical agent.This modification may be total or only partial, that is to say, brought on overthe entire coloured surface, or only in certain portions thereof, as limited bythe engraving roller. In order to illustrate this process the following par-ticulars may serve :—1. Some stripes or any other design is printed on inacetate of alumina prepared for rose-red and mixed with nitrate of alumina.If after drying there is next printed on a finer design with acetate of soda, thissubstance wherever it comes into contadt with the mordant first applied willcause double decomposition to take place between the nitrate of alumina andthe last-named salt, and the result of this decomposition will be to giveincreased strength to those portions of the mordant where such contadt withthe acetate took place. Consequently the effedt after dyeing will be the pro-duction of a double rose-red. Similar effedts can be obtained with the ironmordants, and in that way double purples are produced. 2. Intersectingstripes of purple or red will at the points of intersection have a deeper colourby a similar application suitably executed. 3. Rose-red and purple may bemodified by the addition of catechu to the mordants, and afterwards a designin bichromate of potassa may be printed on. Wherever this latter materialcomes in contadt with the previously applied mordants the oxidation of thecatechu will cause it to develop its peculiar brown colour, but over the rest ofthe pattern it will disappear by means of washing immediately after theapplication of the bichromate, so that on leaving the dye-beck the maddercolours will have only become developed just as if the catechu had not beenadded to the mordant. 4. A mordant for good red is printed on, dyed, andcleared, and next upon some portions of the same fabric a solution of oxalicacid is printed on, the cloth is next steamed, and by this means the adtion ofthe oxalic acid is brought into full force, and wherever it has been appliedthe red colour is converted into rose-red. 5. By crossing stripes of a redmadder-dyed and cleared pattern by means of iron buff stripes, we shall havethree different shades of colour, viz.—A, red not adted upon ; B, buff upon awhite ground; and C, the shade of colour due to the superposition of red andbuff. If there be next applied to this a pattern or impression of oxalic acid,and the fabric afterwards steamed, the effedt will be as follows:—The buffwill have been destroyed, upon the white as far as the acid came into contadttherewith ; where the red, the buff, and acid meet violet will appear, fromwhich it may be inferred that the acid dissolves the alumina in preference tothe iron, and consequently gives rise to the formation of a lake having thatoxide as base. 6. Fine red stripes are first dyed by means of madder towhich nut-galls have been added, the tannin thereof fixed to the mordantand which has resisted the clearing operations is invisible, the only effedtbeing that it slightly alters the peculiar beauty of the red ; but if after the