This section is from the "The elements of drawing & the elements of perspective" book, by J. M. Dent & Sons. Also see Amazon: The Elements Of Drawing & The Elements Of Perspective.
If you rub out any of the pencil inside the outline of the letter, retouch it, closing it up to the inked line. The straight lines of the outline are all to be ruled1, but the curved
Artists who glance at this book may be surprised at this permission. My chief reason is, that I think it more necessary that the pupil's eye should be trained to accurate perception of the relations of curve and right lines, by having the latter absolutely true, than that he should practise drawing straight lines. But also, I believe, though I am not quite sure of this, that he never ought to be able to draw a straight line. I do lines are to be drawn by the eye and hand; and you will soon find what good practice there is in getting the curved letters, such as Bs, Cs, c, to stand quite straight, and come into accurate form.
All these Exercises are very irksome, and they are not to be persisted in alone; neither is it necessary to acquire perfect power in any of them. An entire master of the pencil or brush ought, indeed, to be able to draw any form at once, as Giotto his circle; but such skill as this is only to be expected of the consummate master, having pencil in hand all his life, and all day long, hence the force of Giotto's proof of his skill; and it is quite possible to draw very beautifully, without attaining even an approximation to such a power; the main point being, not that every line should be precisely what we intend or wish, but that the line which we intended or wished to draw should be right. If we always see rightly and mean rightly, we shall get on, though the hand may stagger a little; but if we mean wrongly, or mean nothing, it does not matter how firm the hand is. Do not therefore torment yourself because you cannot do as well as you would like; but work patiently, sure that every square and letter will give you a certain increase of power; and as soon as you can draw your letters pretty well, here is a more amusing Exercise for you.
Choose any tree that you think pretty, which is nearly bare of leaves, and which you can see against the sky, or against a pale wall, or other light ground: it must not be against strong light, or you will find not believe a perfectly trained hand ever can draw a line without some curvature in it, or some variety of direction. Prout could draw a straight line, but I do not believe Raphael could, nor Tintoret. A great draughtsman can, as far as I have observed, draw every line but a straight one.The looking at it hurt your eyes; nor must it be in sunshine, or you will be puzzled by the lights on the boughs. But the tree must be in shade; and the sky blue, or grey, or dull white. A wholly grey or rainy day is the best for this practice.
You will see that all the boughs of the tree are dark against the sky. Consider them as so many dark rivers, to be laid down in a map with absolute accuracy; and, without the least thought about the roundness of the stems, map them all out in flat shade, scrawling them in with pencil, just as you did the limbs of your letters; then correct and alter them, rubbing out and out again, never minding how much your paper is dirtied (only not destroying its surface), until every bough is exactly, or as near as your utmost power can bring it, right in curvature and in thickness. Look at the white interstices between them with as much scrupulousness as if they were little estates which you had to survey, and draw maps of, for some important lawsuit, involving heavy penalties if you cut the least bit of a corner off any of them, or gave the hedge anywhere too deep a curve; and try continually to fancy the whole tree nothing but a flat ramification on a white ground.. Do not take any trouble about the little twigs, which look like a confused network or mist; leave them all out1, drawing only the main branches as far as you can see them distinctly, your object at present being not to draw a tree, but to learn how to do so. When you have got the thing as nearly right as you can, - and it is better to make one good study, than twenty-left unnecessarily inaccurate, - take your pen, and put a fine outline to all the boughs, as you did to your letter, taking care, as far as possible, to put the outline within the edge of the shade,so as not to Or, if you feel able to do so, scratch them in with confused quick touches, indicating the general shape of the cloud or mist of twigs round the main branches; but do not take much trouble about them.
We make the boughs thicker: the main use of the outline is to affirm the whole more clearly; to do away with little accidental roughnesses and excrescences, and especially to mark where boughs cross, or come in front of each other, as at such points their arrangement in this kind of sketch is unintelligible without the outline.
It may perfectly well happen that in nature it should be less distinct than your outline will make it; but it is better in this kind of sketch to mark the facts clearly. The temptation is always to be slovenly and careless, and the outline is like a bridle, and forces our indolence into attention and precision. The outline should be about the thickness of that in Fig 4., which represents the ramification of a small stone pine, only I have not endeavoured to represent the pencil shading within the outline, as I could not easily express it in a woodcut; and you have nothing to do at present with the indication of foliage above, of which in another place. You may also draw your trees as much larger than this figure as you like; only, however large they may be, keep the outline as delicate, and draw the branches far enough into their outer sprays to give quite as slender ramification as you have in this figure, otherwise you do not get good enough practice out of them.