The letters were originally painted on the surface of the papyrus, parchment, board, or other material so employed—the ink not being imbibed or absorbed by the substance on which it was shed, but remaining on the surface, capable of being removed by washing, scraping, rubbing, or any similar process. The surface thus cleansed was then in a state to receive a new inscription; so that erasions and inscriptions might be indefinitely repeated upon it, as upon a modern sign-board.
MODERN INK, on the contrary, leaves its marks upon paper, parchment, &c., by penetrating the material to such a depth that it cannot be erased (mechanically) without the removal or destruction of the surface which it has _tinged_. Chemical agency, as of various acids, chlorine and its compounds, is generally employed, therefore, to discharge the color from modern writing-ink-marks. CARBON, in all its common forms, (charcoal, bituminous coal, anthracite, jet, plumbago, lignite, ivory-black, lamp-black and soot,) is wholly unalterable in color by any of these chemical means.
PRINTING INK (which is composed of carbon suspended in a drying oil) is, in essential characteristics, identical with the writing-inks of the ancient Romans and Greeks. It is impressed upon the surface of paper, (that which is _unsized_ or bibulous being commonly preferred,) and is retained unchanged by the action of moisture, on account of the insolubility of the carbon and the repulsion between oil and water. These two forms of ink are therefore the exact opposites of each other, in the qualities on which their use and permanence depend. The most important peculiarity of the modern writing-ink, as contrasted with the ancient, naturally suggested the two names which it bore in the Latin and Greek of the middle ages, or (to speak more definitely,) the time of its invention and first employment. It was a _Tincta_, a DYE, or STAIN, which _tinged_ and _tinctured_ the material on which it was placed, entering among its fibres as coloring fluids do into cloth in the ordinary processes of manufacture. It penetrated the substance of the paper (as caustics or powerful chemical solvents and corrosives act on the organic fibre): it _bit in_, or _burned in_,—and was therefore well named ENCAUSTON and _Incaustum_.