Page:TheAmericanCarbonManual.djvu/24

 be desirable to give a brief summary of the grounds for stating that permanency is secured in the method of printing to be described. They are these: the image is formed of carbon or other known permanent pigment; the vehicle or menstruum in which the pigment is held is gelatine, rendered quite insoluble by combination with the oxide of chromium; the amount of gelatine present in the image, and uniting it with the paper on which it rests, is not greater than that on the surface of a sheet of well-sized writing-paper, so that there is as little danger of the vehicle cracking or decomposing, as there is of the pigment fading. Absolute imperishability cannot probably be predicated of any picture formed of pigments and paper; but, as much permanency may be anticipated for these prints as is found to pertain to an Indian-ink drawing, to which experience permits us to award a duration of at least several centuries.