With the invention of this medium new possibilities came into the world, and a continual succession of painters have been inventing ways of putting on paint, the result being the stock of methods and processes of handling which are the groundwork of the art of painting to-day.
From time to time there have been groups of artists who have used common methods, and who have developed expression through those methods which became characteristic of their epoch; and because the resulting pictures were of a high degree of perfection, their methods of handling acquired an authority which had a very determining effect on different periods of painting.
In this way have come those ideas as to what kind of painting or what ways of putting paint on canvas should be accepted as "legitimate." And the methods accepted as legitimate or condemned as illegitimate have been varied from time to time—those condemned by one period being advocated by another; and the processes themselves have been almost as varied as the periods or groups of men using them.
In the long run, methods and processes have received such authoritative sanction from having been each and all used by undoubted masters, that they have become the traditional property of all art, which any one is free to use as he finds need of them. They have become the stock in trade of the craft.
The artist may use them as he will, provided only he will take the trouble to understand them. He must understand them, because the manipulations which make up these different processes accomplish different effects and different qualities; and as the painter aims at results, if he does not understand the result of a process when he uses it, he will get a different one from that which he intended.
The painter should not be hampered by process; he should not be controlled in the expression of himself by tradition. He should feel free to use any or all means to bring about the result he aims at, and he should allow no tradition or point of view to prevent him from selecting whichever means will most surely or satisfactorily bring about his true purpose.
Of course there are many ways of using paint which are unsafe. Some pigments are unsafe to use because they either do not hold their own color, or tend to destroy the color of others. You should always bear this in mind; and if you care for the permanence of your work, you should not use such materials or such processes as work against it. But beyond this, the whole range of the experience and experiment of the workers who have gone before you are at your command, to help you to express yourself most perfectly or completely; to represent whatever of visible beauty you may conceive or perceive.
And this is the whole aim of the painter; to stand for this is the whole purpose of the picture.