These three colors are at the same time semi-opaque, their opacity being just sufficient to tint the hard black of the coal, while never clogging or muddying its transparency.
So it is with the millions of other tones in the whole composition, when such perfectly transparent colors as brown madder, Indian yellow, and indigo are used as a glaze, altering and modifying the undertone of charcoal to any desired tint and at the same time preserving the all-important thing--its transparency.
In conclusion, let me say that I fully recognize that I am addressing students whose training enables them to understand perfectly this explanation, and that further instructions are therefore unnecessary.
One thing, however, may be accentuated, and that is the use of plenty of clean water. Another is that you should keep your palettes separate. For myself, I make use of a common white metallic dinner-plate, known as iron-stone china, costing another ten cents, for my sky-palette, squeezing the color-tubes in a row around its edge and my Chinese white below them on one side toward the bottom. For my transparent palette, I use an ordinary moist sixteen-pan color-box, being always careful never to blur it with even a brush stroke of body color (Chinese white); and for my opaque work, an oval white metal palette, with thumb-hole, and indentations around its edge into which I squeeze the contents of my moist water-color tubes, my Chinese white being heaped up in a little mound near my thumb.
The result may be seen in some of the illustrations accompanying this text.
Before going into the value of charcoal as a medium in the recording of the various aspects of nature in black-and-white, it will be wise to review the several mediums in general use, namely, etching, pen and ink, lithographic crayon, and charcoal gray in connection with Chinese white; it will be well, also, to note the various mechanical processes in use for the reproductions of these drawings on white paper.
Those of you who have seen the early illustration in _Harper's Magazine_ of the late fifties will recall the work of "Porte Crayon" (Colonel Strother), drawn on wood by the artist and engraved by such men as A. V. S. Anthony and John Sartain. You will also recall how some twenty-five years later an effective and marvellous change took place in the quality of these reproductions, being by far the most unique and rapid in the history of any art of the century. In less than ten years, between 1876 and 1886, came this sudden awakening to the necessity of better work from the burin, followed by an enormous commercial demand for such results, until by common consent the American engraver first rivalled and then surpassed the world. If we search for the cause we find that, like many other inventions developing others of still greater importance, as the telegraph developed the telephone, electric light, and the phonograph, this marvellous change is due entirely to the discovery and possibility of photographing direct from the original upon the boxwood itself, producing with an instant's exposure a complete reproduction of the original drawing, with all its texture, gradation, and quality, not only doing away entirely with the intermediate draftsman, as was the case with "Porte Crayon's" work, but obtaining a result impossible to the most skilful of the artists on wood of his day.