Circles flirt with cylinders and flat squares dance with cubes in Lucy Clark's new oils, now on exhibition at the Baumgartner Galleries, 2016 R St. NW.

Her hollow tetrahedrons rhyme with triangles and pyramids. The floating elemental forms -- paying no attention to the somber laws of gravity or to dull consistency -- oscillate between two and three dimensions, or change their pastel colors from beige to gray and back again like so many Euclidean chameleons. These handsome pictures show us geometries at play.

Abstrct painters have for years tried to find a common ground between spontaneity and plan. Many in the past have tethered their geometries to liberate their colors. The late Josef Albers would not tilt his squares, though his hues were wild; the just-as-joyous colors of Washington's Gene Davis play inside striped prisons. Clark, who here breaks parallel and renders three dimensions, has found another place between the rigid and the free.

Her pictures are beguiling. What dulls them just a little is the way she puts on paint. Look, for instnace, at the surfaces of the picture she calls "Summertime." The rather rough impasto of that small yellow triangle makes that floating shape look as if it were hammered out of gold. But the freely brushed impasto of the field that surrounds it is far less successful. That larger painted panel seems filled in with scribbles. Her arbitrary brush strokes and the glints of light that they throw off irritate the viewer. The rightness of that painting is undercut by chaos, nibbled at by mess. Clark has worked for three years on the pictures in this show. She has never displayed finer work. Her exhibition closes on Nov. 8.

Joseph Beuys, whose prints are now on view at the Sander Gallery, 2600 Connecticut Ave. NW, is Germany's most admired living artist -- though if you only knew his art from the works on paper here you would not understand why.

His major works -- his sculptures and performances -- suggest an enigmatic blend of autobiography, social commentary and Germanic myth. In them Beuys employs remarkable materials. He might, for example, spend hours in a gallery with a live coyote, or employ materials as wholly unexpected as sleighs or piles of newspapers. Volkswagen vans or his own body.

His champions may contend that these lesser works on paper resonate mysteriously with his sculptures and performances and with his own history. Those who know that Beuys almost froze to death when shot down during World War II, and that his life was saved when those who found him wrapped him round with gobs of animal fat, may see the print that he calls "Fat Filled Sculpture" as a haunting work of art. But to others, it will seem, as do the rest of the scribbles here, just a sloppy doddle. These works resemble meticulously printed replicas of quickly jotted watercolor sketches. The titles that he gives them -- "Tent With Light Beam," "Woman Runs With Brain," "Calf With Children," "Hand That Swears" -- are vastly more evocative than the prints themselves. There are 20 of them here, in this his first solo show in Washington. It closed Oct. 18.

Though hard-edge Washington Color Painting is no longer much in fashion here, Elliott Thompson -- whose paintings are on view at the Barbara Fiedler Gallery, 1621 21st St. NW -- has with dogged loyalty remained true to his straight edge, his masking tape, his panels of flat, well-chosen colors. His pictures here are strong, energetic, crisp.

He displays two sorts. Those on the gallery's first floor are shaped canvases that zoom diagonally across the wall like brightly colored roadways seen in perspective. The three narrow paralled colored lines, that runs down their centers divide them into two, as the stripes of two-lane highways divide the road. The sense of rush, of accelerating speed, set up by the pictures' shape, is heightened by the flicker, the electric op-art zing, that his colors generate. The light blue lines that bisect the painting he calls "Orange" tend to somehow bleach that road-like field of bright orange red; the narrow stripes of darker blue lend a strip of purple haze to the picture he calls "Fayence."

The works on view upstairs obey another format. These canvases are square, and the lines and squares (and sometimes cubes) of black and white and beige and gray that one finds within them are tightly locked in place. They sometimes look like tiled planes; at other times they call to mind arrangements of stacked cubes seen in isometric perspective. No handwriting disturbs their perfectly smooth surfaces. Thompson does not play; the paintings he is showing are the opposite of messy. Instead, they have the tension and the glean of a stainless steel wire pulled absolutely taut. His show closes Oct. 28.