In drawing a problem, proceed, with the pencil sharpened to a point, to lay down the several lines until the whole figure is completed, observing to let the lines cross each other at the several angles, instead of merely meeting. By this, the length of every line will be clearly defined. With a drop or two of water, rub one end of the cake of ink upon a plate or saucer, until a sufficiency adheres to it. Be careful to dry the cake of ink; because if it is left wet it will crack and crumble in pieces. With an inferior camel's-hair pencil add a little water to the ink that was rubbed on the plate, and mix it well. It should be diluted sufficiently to flow freely from the pen, and yet be thick enough to make a black line. With the hair pencil place a little of the ink between the nibs of the drawing-pen, and screw the nibs together until the pen makes a fine line. Beginning with the curved lines, proceed to ink all the lines of the figure, being careful now to make every line of its requisite length. If they are a trifle too short or too long the drawing will have a ragged appearance; and this is opposed to that neatness and accuracy which is indispensable to a good drawing. When the ink is dry efface the pencil-marks with the india-rubber. If the pencil is used lightly they will all rub off, leaving those lines only that were inked.
In problems all auxiliary lines are drawn light; while the lines given and those sought, in order to be distinguished at a glance, are made much heavier. The heavy lines are made so by passing over them a second time, having the nibs of the pen separated far enough to make the lines as heavy as desired. If the heavy lines are made before the drawing is cleaned with the rubber they will not appear so black and neat, because the india-rubber takes away part of the ink. If the drawing is a ground-plan or elevation of a house, the shade-lines, as they are termed, should not be put in until the drawing is shaded; as there is danger of the heavy lines spreading when the brush, in shading or coloring, passes over them. If the lines are inked with common writing-ink they will, however fine they may be made, be subject to the same evil; for which reason india-ink is the only kind to be used.