If possible, the stone should be allowed to rest for a day or two after proving, in order that the ink may sink well in. Before printing, the gum is washed off and the stone allowed to remain in the press-room until its temperature is the same as its surroundings. The stone is then thoroughly and evenly damped all over, placed in the press, and rolled up with lithographic ink; the paper is then laid on, and the whole passed through the lithographic press. After the first few pulls it will be seen whether all is well. The essentials of a good impression are these: the lines must be black and not grey, provided black ink is used; the lines must not be wider or blacker ("smutty") than those on the stone, nor must they be ragged or broken ("rotten"). In printing, the stone must be damped and inked before each impression is taken, and occasionally re-gumming is required. Good printing requires a considerable amount of ability, especially in the case of crayon drawings. The paper used is a very important matter, the selection of which can be safely left to the lithographer, provided he be a good one, unless the author possesses the necessary technical knowledge. If a smooth paper is required, and the paper is not to be damped before printing, India paper is best and plate paper next best. All coarse or grained papers must be damped before printing. As has already been remarked, lithography is a good process for scientific work; but, unfortunately, considering the number of lithographic plates published, really first-class examples are rare. This is largely due to the original draughtsman; it is unreasonable to expect a lithographer, in all probability ignorant of the subject of the plate, to turn out first-class reproductions of drawings which are obviously bad. On the other hand, lithographers vary greatly in their capabilities, and indifferent plates may be entirely due to their ability not being first rate. As drawings have to be traced, mistakes are apt to occur; the proofs should, therefore, be carefully examined, for a certain amount of correction can be made on the stone. The following works contain excellent lithographs, which should be studied by those interested in the subject. Bornet et Thuret: _Notes Algologiques_. Paris, 1876-1880. This contains some of the best work, illustrative of science, known to the present author. The original drawings mostly were made by Bornet, and the lithography was carried out by Riocreux--one of the best if not the greatest of botanical artists--Arnoul, Picart and Pierre. Davis and Thurnam: _Crania Britannica_. London, 1865. Mirbel: _Sur le Cambium_, Paris, 1842. The plates provide excellent examples of ink lithography by Laplante. Von Mohl: _Schriften botanischen Inhalts_. Tuebingen, 1845. Good examples by Federer. The first volumes of the _Annales des Sciences Naturelles_ (Paris) may be referred to for lithographic work earlier than the above (1820).