Yuriko Yamaguchi does it again. As usual.

Of the hundreds of pieces of sculpture around town for the International Sculpture Conference last week, precious few were worth the time and effort it took to put them up. The irony of this is brought home merely by walking into Yamaguchi's small exhibit at the Middendorf Gallery. This artist says more of substance with only four wall pieces of carved and painted wood than nine-tenths of all the tons of glass, metal and stone littering this city thanks to the ISC.

Far larger and more of a piece than the multi-object assemblages she was making several years ago, these new works -- three of the "Rejuvenation" series and one of the shelflike "Source" pieces -- retain Yamaguchi's immediately recognizable derivations of organic form. Her preferred elements of egglike shapes, leaves, carved branches, replicated stone textures and so forth are always in evidence. Yet,because of her endless inventiveness, these never become tendentious nor lose their ability to intrigue with subtlety.

Nuance, in fact, is the very stuff of Yamaguchi's art. And, as odd as this may sound in reference to pieces of sculpture, these new works are largely about transparencies. Take the big "Rejuvenation #6," one of several variations on the same theme. A vaguely triangular composition of a carved and painted grouping of "stones" over which hover a long "leaf" and an elbowed "branch," the work invites the viewer to imagine water between the surface elements and the patterned background. Water, in other words, upon which floats a leaf and twig, and through which we see the pebbles of a stream bed.

Like the others in this series, "Rejuvenation #6" is, in effect, a magnified slice of nature, cut out, detached and presented as a three-dimensional art object. The stages of the metamorphosis -- the process by which the artist realizes her concept -- are left for the viewer to discover. The marks of the chisel, the abraded areas under the paint are never wholly finished or concealed. The telltale signs of the creative process are as important to the finished work as to the business of making it.

So it is that with Yamaguchi's art, the transparencies are not merely a matter of implication in the form of the art object itself, but of metaphorical layerings of source, method and artifact.

'Sculpture '90'

Although there are a few impressive works in "Sculpture '90," a juried exhibition of 29 contemporary sculptors at Washington Square, for the most part it's a disappointing show.

There are some respectable talents represented here, but without any attempt by the organizers to aim for some theme or focus, even such artists as Steve Bickley, John Gregory Flowe and Karen Kincaid are damned by association. The only works that truly leave an impression are those that, by a fortuitous combination of originality and placement, manage to hold their own against the overwhelming mediocrity. Whatever inspired the organizers of this exhibit to place Marc Robarge's ominous yet graceful "Birthplace IV" -- a wooden, Norman window-shaped open chapel of sorts with a discreet vulvate opening -- a few paces away from Greg Moring's insipid Frank Stella knock-off "What Goes Around, Comes Around" is beyond this critic. It's a bit like putting a fine Hepplewhite chair at a linoleum-topped card table.

The same problem dogs most of this show. The urge to place as many different types of contemporary sculpture together in one show is understandable, but stupid. It's even dumber when the difference in quality -- between, say, Alison Jones's haunting carved wood figures and Lynn Feinstein's silly pop art cutouts -- is so vast.

'Nuff said. If you visit this show -- and if you work in the building you don't have much choice -- there are several pieces well worth the time to seek out. Mary Scrupe's painted steel and brass composition "Worker" is an impressive piece, as is Robert John Devers's polychromed terra cotta sculpture "Anima." Andrew Krieger's small, painted cutaway interior scenes, two of which palliate this hodgepodge show, are always delightful. Maria Eugenia Bigott's large wood sculpture "Retrato En Familia" is hard to miss, and is a very fine effort, as is Mary Giehl's elegant "Acidic Tree" of wood, copper and steel. And be sure to visit Allen Linder's stunning bit of craftsmanship in pink marble, pewter and paint, "Sitting Man." An acrobat in pink tights, he sits cross-legged, his lifelike eyes staring out at the ceiling -- appalled or stunned, it's hard to tell.

Photos at Kathleen Ewing

At the Kathleen Ewing Gallery, the exhibit "From the Air" offers a host of early 20th-century and contemporary aerial photographs, as well as some vintage pictures of vintage aircraft. This is not a show to send modern experimental photographers scurrying for new techniques, but it's fun to visit nevertheless.

The old pictures of airplanes, cities and World War II air combat by William Preston Mayfield and others -- many of them anonymous -- are more curiosity items than anything. But many of the recent aerial shots by Marilyn Bridges, William Garnett, Frank Gohlke and Alex MaClean are truly beautiful images. Gohlke's impressive black-and-white pictures of Mount St. Helens several years after the big blow in 1980 communicate the extent of the devastation.

Bridges' rich silver photographs of various topographical anomalies in the United States, England and Peru create vivid random patterns, as do Garnett's lovely compositions. Garnett has a way of capturing the folds of a sand dune to make it look startlingly like a discreet portion of a beautiful woman's anatomy.

MaClean's big Cibachromes of tilled farmland studded with red barns in late afternoon light may sound corny in description, but are in fact striking works.

Yuriko Yamaguchi, at Middendorf Gallery, 2009 Columbia Rd. NW, through July 7.

Sculpture '90, at Washington Square, 1050 Connecticut Ave. NW, through Sept. 7.

From the Air, at the Kathleen Ewing Gallery, 1609 Connecticut Ave. NW, through July 28.