Volume 1
A course of lectures on natural philosophy and the mechanical arts / by Thomas Young.
- Thomas Young
- Date:
- 1845
Licence: Public Domain Mark
Credit: A course of lectures on natural philosophy and the mechanical arts / by Thomas Young. Source: Wellcome Collection.
Provider: This material has been provided by King’s College London. The original may be consulted at King’s College London.
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![of points through it, so as to mark the copy, either at once, or by means of charcoal powder rubbed through the holes, which is called stenciling : and for this purpose, an intermediate copy may be formed on semi-trans- parent paper. Another method is to put a thin paper, nibbed with the powder of black lead or of red chalk, between the original and the paper intended for the copy, and to pass a blunt point over all the lines to be traced, which produces correspondent lines on the paper; tliis is called calking. Where the work is large, it may be covered with a thin gauze, and its outlines traced on the gauze with chalk, which is then to be placed on the blank surface, and the chalk shaken off it in the way that a car- penter marks a board with his line.* The pen was formerly much used for making rough sketches, and it is still sometimes employed for the same purpose, as well as for assisting the effect of the pencil. The appearances of uniform lights and shades must necessarily be imitated in drawings with the pen, as well as engravings, by a mixture of the whiteness of the paper with the blackness or colour of the ink, the eye being too remote to distinguish minutely the separate hues by, which the effect is produced, although they do not entirely escape its observation. In this respect, drawings in pencils and chalks have an advantage over engravings ; these substances, after being laid on in lines, are spread, by means of rubbers or stumps, of paper, leather, or huen, so as to produce a greater unifoimity of tint. Some, indeed, are of opinion that engravings derive a great brilliancy from the hatches that are employed in shading them, and that minute inequalities of colour make every tint more pleasing. In drawings with chalk, however, the advan- tage of rubbers is unquestionable. The lines of a drawing may be made to have an appearance of gi-eater freedom than those of an engraving; they should be parallel, and when they are crossed [the different sets should be] moderately oblique to each other ; their direction should be governed by that of the outline. Engravings in mezzotinto exhibit no lines : but they are deficient in spirit and precision : the effect of aqua tinta approaches much nearer to that of drawing, and it has a similar advan- tage in the mode of producing its lights and shades. (Plate VI. Fig. 79.) It is well known, that the best pencils are made of English black lead, or plumbago. Of black chalks, the Italian is harder and moi’e generally useful than the French : red chalk has the disadvantage of not being easily removed, either by bread or by Indian rubber, without leaving a brownish mark. All these chalks are of the nature of a soft schistus or slate ; they may be made to adhere firmly to the pajjer by dipping the drawings in milk fi’eed from cream, or even in water only, which dissolves the size or gum of the paper. Sometimes a grey paper is used, which serves for a middle tint, and lessens the labour, the lights and shades only being added in white and black chalks. Crayons consist of colours mixed up with gum water, or other adhesive substances, and usually .also with some chalk, plaster, or pipe clay, so as to be of a proper consistence for working in the manner of chalks. The * Imison’s Elements, ii. 240, 327.](https://iiif.wellcomecollection.org/image/b21301840_0001_0106.jp2/full/800%2C/0/default.jpg)
