The many masks of modern art

Two things are obvious about Charles Sheeler's ''Interior, Bucks County Barn'': It's an exquisite black-and-white drawing, and it couldn't have been done before the days of photography.

It is not, however, slavishly photographic, for Sheeler put his own very personal draftsman's touch upon it. It may derive from the way the camera records things, but it also has many of the finer characteristics of pure drawing.

Unlike most artists of his generation, Sheeler saw the painter and the photographer not as natural enemies but as creative brothers. He himself, as a matter of fact, was proficient and professional in both art forms, and he practiced them with equal seriousness. More important, he saw no reason to keep them separated, and he frequently adapted the principles and procedures of the one to the other - even to the point of translating some of his photographs into paintings, drawings, and prints.

I'm not positive that ''Interior, Bucks County Barn'' was derived from one of his photographs, but I strongly suspect it was. It certainly resembles a photograph in many ways. And yet, I couldn't care less, for Sheeler made many subtle alterations to make it a drawing. We also mustn't forget: If he did use a photograph, it was one of his own. Photograph or drawing, the work's conception was Sheeler's, not someone else's.

I suspect that Sheeler took the photograph first as a finished work of art and then felt challenged to transform it into a drawing. In other words, he saw the drawing as an extension of the photograph, as a hand-drawn modification made in his studio with crayon and paper rather than in the darkroom with photographic chemicals and equipment.

In this he was quite revolutionary. The use of photographs as source and reference material was, of course, not new. Painters and sculptors had been utilizing them in this fashion almost from the moment the camera was invented. But they had always gone to great lengths to disguise or deny this fact. To base a painting on a photograph, after all, was a prime artistic sin until the days of the Photo-Realists, and deliberately to accept a photographic ''look'' as a formal premise for a drawing was to risk outright ridicule or contempt.

Sheeler, however, saw things differently. For him the camera was a perceptual tool with almost limitless use. It didn't make sense, therefore, not to use it to improve his drawings, or to expand their range.

Fortunately, Sheeler didn't fall into the popular trap of accepting photographic truth as ultimate perceptual truth. He was aware that the camera is indifferent and mindless, that without a human sensibility and intelligence to guide it, it remains nothing but a fascinating toy. He was aware (and one can only wish that the Photo-Realists had been as aware) that a photograph can be the worst kind of dead end for a painter. That, in the hands of a lazy or insensitive painter or draftsman, a photograph used as a model can very literally mean the end of genuine creativity.

Sheeler, however, was neither lazy nor insensitive. In almost every instance, his drawings are starker and crisper, more concentrated and ''pure,'' than his photographs. If he removed a detail here and there, altered a texture or strengthened a line, it was to give the work a clearer identity as a drawing.

His goal was always to fashion a more ''perfect'' image, to come as close as possible to creating icons of everyday or industrial reality. And to do so with maximum authenticity and impact.

To this end, he used photographs for authenticity, the principles of design and dramatic contrast for impact. He hoped, by playing them against one another, to produce paintings and drawings that both universalized their subjects and defined them as very real objects and places in the here-and-now.

He succeeded particularly well in ''Interior, Bucks County Farm.'' It's a minor masterpiece of black-and-white patterning and design that also takes full advantage of photographic effects.

Nothing looks more real and solid, for instance, than the buggy at the center. And yet, where is its right front wheel? All we have in its place is an ambiguous area of grays that could be almost anything. As we study it, however, we become aware of how cluttered this area would be had Sheeler included the wheel. And so he left it out, compensating for its absence with a series of visual devices: He strengthened the patches of sunlight on the wall immediately to the left of where the wheel should be, and darkened both the objects on the pegs and the short board rising above them. This carefully worked-out illusion satisfies the eye's need for balance, removes a problem area in the composition, creates a more harmonious flow of texture and tone, and does so without sacrificing one iota of authenticity or ''truth.''

The entire composition is full of such subtle illusions and adjustments. How, for instance, is the buggy's front left wheel attached? The answer is that it isn't, and yet our eyes ''read'' it as firmly attached. And where would anyone sit in this buggy? Or harness it and attach it to a horse?

The more we study this drawing, the more ''abstract'' and unreal - and the more exquisitely and shrewdly designed - it becomes. Forms are moved a bit to the right or left to create more interesting patterns, or to lead the eye in a particular direction. Note, for instance, how subtle and crucial the inward curve on the vertical plank at bottom right is, and how essential the short, light board above it is in diverting the eye from the harsh dark angle of the doorway. Even the shading throughout is delicately modulated to focus our attention, or to draw it away to something more important.

And yet, the moment we stop analyzing it, the drawing immediately becomes photographically ''correct'' and authentic once again. And all of Sheeler's subtle adjustments are forgotten in the light of the ''truth'' that lies before us.

That is the magic of Sheeler's art, and the reason he cannot be described as an artist who copied photographs. He used them, true enough, but only as a guide and frame of reference. He was an artist, first and foremost, and the fact that he used photographs as the basis for some of his works is of no more importance than that Holbein drew from real people, or that Braque created collages out of newspaper headlines and ticket stubs. Art, after all, is not determined by one's choice of materials or subjects but by what one does with them.

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