Still, by way of finale, we would offer a few remarks. In no branch of the science, perhaps, is it more hazardous to commit oneself to a positive dictum than in the chemistry of colours, so liable are theory and practice to clash, and so often does the experience of one person or one time differ from that of another. He who has turned his attention to pigments, finds nearly every assertion must be qualified, for to nearly every rule there is some exception, and learns that theory alone may mislead. For example, a colour known to be fugacious may last, in certain cases, a surprisingly long time; while, on the contrary, a pigment permanent when used alone, may be rendered fugitive by improper compounding. Again, what holds good of a colour produced by one process, or employed in one vehicle or by one artist, may not be true of the same colour made by a different mode, or used in another vehicle or by another artist. It is because, then, colours are of every degree of durability, from the perfectly stable to the utterly fugitive, and because each one is liable to influence by every condition of time, place, and circumstance, that the chemist's theory is opposed as often to the painter's practice as the experience of artists themselves varies. This may explain the charges of inconsistency and contradiction which have been brought against writers on pigments, faults that lie rather with the nature of the subject than with the authors. Even at the risk of being tiresome, we have throughout insisted on the choice of permanent pigments, not simply for use alone but for mixed tints. To quote Cennini, "I give you this advice, that you endeavour always to use ... good colours.... And if you say that a poor person cannot afford the expense, I answer, that if you work well (and give sufficient time to your works), and paint with good colours, you will acquire so much fame that from a poor person you will become a rich one; and your name will stand so high for using good colours, that if some masters receive a ducat for painting one figure, you will certainly be offered two, and your wishes will be fulfilled, according to the old proverb, 'good work, good pay.'" Of a truth, if man cannot dip his brush in the rainbow and paint with the aerial colours of the skies, he can at least select the best pigments that earth and the sea afford him; preferring, where he cannot get brilliancy and permanence combined, sobriety and permanence to brilliancy and fugacity. It must be the wish of every real artist to leave behind him a lasting record of his skill, a permanent panorama of those hues of nature which in life he loved so well. To effect this, genius alone is powerless: there must be first a proper choice of materials, and next a proper use of them. The painter's pigments are the bricks wherewith the mortar of his mind must be mixed, either to erect an edifice that shall endure for ages, or one which will quickly topple over like a house of cards.