Besides the painting-brush and the feather-pen, the other instruments used in the decoration of vases include the pointed graving-tools employed for incised lines, modelling-tools for the parts in relief, a stick for steadying the hand while at work, and a pair of compasses. The latter were employed for marking circles, as may be clearly seen on shields on the B.F. vases, where the mark left by the central point of the compasses is often visible. The difficulties in the painting of Greek vases must have been numerous. In the first place, it was necessary for the artist to finish his sketch with great rapidity, since the clay rapidly absorbed the colouring matter, and the outlines were required to be bold and continuous, any joins producing a bad effect. Again, the vases were often painted while in an upright position, and the artist was obliged to stoop, rise, and execute his work in these difficult attitudes; nor could he remove the pencil from any figure which he had once begun. The eye must have been his only guide. Then, as he was obliged to draw his outline upon a damp surface, the black colour which he used was instantly confounded with the tint of the clay. The lines grew broad at first, and afterwards contracted themselves, leaving but a light trace, so that the artist could with difficulty discern what he had been doing. Moreover, the lines, once begun, could not be left off except where they met other lines which cut or terminated them. Thus, for example, the profile of a head must have been executed with a single continuous line, which could not be interrupted till it met the neck; and in drawing a thigh or leg, the whole outline must have been finished without taking off the pencil: proceeding from the top downwards, making use of the point to mark the horizontal lines, and afterwards rising upwards to finish the opposite side. The drawing was done entirely by the hand and no pattern used. The outlines round the figures on R.F. vases were drawn strongly, in the manner described above, to prevent the background encroaching on the figure. That this was done while the clay was moist appears by the outlines uniting, which could not have taken place if the clay had been dry. It was so difficult to fill in the outlines without alteration, that they were frequently changed, and sometimes the ground was not reached, while at others it exceeded the line. The ancient artists, notwithstanding these difficulties, observed all the laws of balance and proportion, especially ἰσομετρία, or the law of equal height of all figures; conveyed expression by means of attitude; and, by the use of profile, and the introduction of accessories, or small objects, into the background, contrived to compensate for the want of perspective.