But the other, the material, the concrete, the practical, it is the purpose of this whole book to help you to understand and to acquire the mastery of, so far as may be done by words.
Teaching by words is difficult, and never completely satisfactory. But much may be done. If you will use your own brains, so that what does not seem clear at first may come to have a meaning because of your thinking about it, we may accomplish a great deal. I cannot make you paint. I cannot make you understand. I can give you the principles, but you must apply them and think them out.
Everything I say must be in a measure general; for the needs of every one are individual, and the requirement of each technical problem is individual. I must speak for all, and not to any one. Yet I shall state principles which can always be made to apply to each single need, and I will try to show how the application may be made.
=Technique.=--The science of painting consists of a variety of processes by means of which a canvas is covered with pigment, and various objects are represented thereon. The whole body of method and means is called technique; the several parts of technique are called by names of their own. That part which applies to the putting on of the paint may be generally called _handling_, although the word _painting_ is sometimes restricted to this sense, and _brush-work_ is often used for the same thing. The other technical means will be spoken of in their proper place. Let me say now a few words as to _handling_ in general.
Ever since art began, men have been searching for means of fixing ideas upon surfaces. But it is only within the last four hundred years that the processes of oil painting have been in existence--simply because they are peculiar to the use of pigments ground in oil as a vehicle, and the oil medium was not invented until the middle of the fifteenth century.
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.