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business, for which the thickening of the oils in their na-tural state renders them unfit.

XI. Rolling-press Ink.

Between the rolling-press printing, and that of the prin-ters press strictly so called, there is this essential difference ;that in the former the impression is received from figureshollowed in a copper plate, but in the latter from promi-nent types. The damping of the paper is equally neces-sary for the rolling-press as for the other, in order tosoften it, so that the parts, corresponding to the cavities inthe plates, may be forced into them. But the ink is of asomewhat different quality. For while the printers typesrequire a glutinous or sticky mixture, which {hall adhereupon the prominences of the type, without running intothe hollows z the ink for copper-plates must run into andfill the hollows, especially when the plate is warmed,, andbe so little glutinous, as to be easily wiped off clean fromthe smooth parts of the plate, or those which are to leavethe paper white.

The oil, for this ink, must be boiled, and set on fire,in the same manner as for the other, to take off its greaii-ness and promote its drying : the boiling is continuedmore or less, according to the different consistences whichdifferent kinds of plates may require, but never so far asto communicate to the oil the adhesive gluey quality ofthe printers varniih. The black matter must be of tirecharcoal kind : the lamp-black gives always a degree oftoughness, but the charcoal blacks, as they do not uniteintimately with the oil, divide its texture, and render itless gluey. The coal commonly employed for this use isbrought in powder from Germany, and called German orFrankfort black : this is softer, and more free from gritti-

ness,

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