The qualities which make a good study are the reverse of those which make a good sketch. In the sketch all is sacrificed to the effect, or to the one thing which is its purpose. The study is what its name implies, and its purpose is not one thing, but many. In a study you put in everything which may be valuable. You store it with facts. You leave out nothing which you wish to put in. It is all material. You can take and leave in using it afterwards, as you could from nature. Of course every study has some main intention, but you must take the trouble to give everything that goes to the making of that.

A study is less of a picture than a sketch is. For unity of effect is vital to both a sketch and a picture. But this quality is of no essential value in a study—unless it be a study of unity. For you can make a study of anything, from a foreground weed to a detailed interior, from a bit of pebble to a cavalry charge.

But in a study of one thing you concentrate on that thing, you deliberately and carefully study everything in it, while in a sketch you work only for general effect. The study is the storehouse of facts to the painter. By it he assures himself of the literal truths he needs, collecting them as material in color or black and white, and as mental material by his mental understanding of them, only to be gained in this way.

In making a study you may work as long as you please, timing yourself by the difficulty and size of the thing you are studying. A study of an interior or a landscape may occupy a week or two; one of a simple object for some detail in a picture may be a matter of only a few hours. But in any work of this kind you should be deliberate, and remember that what you are doing is neither a sketch nor a picture, but the gathering of material which is to be useful, but which can be useful only so far as it is accurate.

In making studies, don't try for surface finish; get the facts, and leave all other qualities for the picture. Don't glaze and scumble, but work as directly as you can. Study the structure and texture of whatever you are doing. Understand it thoroughly as you go on, and search out whatever is not clear to you. This is no place for effects; nor for slighting or shirking. If you do not do work of this kind thoroughly, you might as well not do it at all—better; for you are at least not training yourself to be careless. There are places where you may be careless, but the making of a study is not that place.

Take plenty of trouble with preliminaries. Get all your foundation work true. Have a good drawing, get the groundwork well laid in, and then build your superstructure of careful study.

Don't be afraid of over-exactness, nor of hardness and edginess here. All that is only an excess of precision, and it is just as well to have it. You can leave it out if you want to in your picture, but a groundwork of exactness is not to be despised.

Be exact also with your values. If your study is not sure of its values, it will weaken the results you should get from it later.

Make your studies in the same light as that which the picture will represent. You can paint a picture under any light you please if your studies give you the facts as to light and shade that the truth to nature requires; but studies made in one light for a picture representing another are useless to that picture.

No good painting was ever made without preliminary studies. When you are to make a picture, therefore, take plenty of time to prepare yourself with all the material in the form of facts that you may require. Don't trust to building up a picture from a sketch or two and your "general knowledge." That sort of thing is something which a painter of experience may do after storing his mind for years with all sorts of knowledge; but it will not do for most people—least of all for a student. And it is a dangerous way for any one to work. Even the experienced painter is apt to do the worse work for it, and if he does so constantly, his reputation may suffer for it. Take time to be right.

Don't be afraid of taking measurements. Every one who did anything worth looking at took measurements. Leonardo laid down a complete system of proportions. You can't get your proportions right without measurements, and if your proportions are not right, nothing will be right. Use a plumb-line: use it frequently, and measure horizontals and verticals. If you are in doubt about anything, stop a minute and measure. It takes less time than correcting.

Whatever you do, get the character first, then the details. Character is not a conglomeration of details. The detail is the incident of character. See what the vital things are first, then search farther.

Use your intelligence as well as your eye and hand. Think as you work. Don't for a moment let your hand get ahead of your brain. Don't work absent-mindedly, nor without purpose. If your mind is tired, if your eye won't see, stop and rest a while. Tired work runs your picture down hill.