WHITE, CREAMY, pure, translucent, resonant -- porcelain has always been counted as the empress of clays. The objects are often called china, as a bow to its first makers, between 600 to 900 A.D.

The Rnewick Gallery surveyed the work now being done by porcelain makers over the entire United States. "American Procelain: New Expressions in an Ancient Art" opened this weekend to show 108 artists who have only the medium in common. The exhibit continues through Aug. 16, 1981.

A definition of porcelain by Jan Axel and Karen McCready (from a book not yet published) is quoted by Lloyd Herman in the catalogue to the show:

"Porcelain is composed of comparatively few ingredients: koalin, the actual caly with the clay; silica or glass; and fledspar, the fluxing agent which causes the materials to fuse. High kaolin and silica content contributes to porcelain's unique quality and, ultimately to its shining, glassy surface. The fact that clay and glaze mature together at high temperature, forming an interlocking entity, is one of the traditionally held definitions of porcelain. iThis relationship gives porcelain its exceptional character among ceramic material."

What the artists in the Renwick show do with the procelain is vastly different. Some of the ceramicists make funky or pop-art peices, figures, jokes -- some amusing, some obscene. These, though they look nothing like, are in the same tradition with the German figurine makers. Only a few are better than kitsch (appropriately a German word for a German craft).

But other objects are as beautiful as any that have been made since the Chinese learned how.

Robert Deutsch's "equinox" pot doesn't look much like porcelain -- thrown and burnished, it is low-pit fired in a wood burning kiln, giving it a deep black-brown color. Lloyd Herman, Renwick director, and author of the excellent essay in the forthcoming catalogue, explains that Deutsch chose porcelain for its workable texture, "a feature many artists describe as being a bit like cream cheese or toothpaste." The pot swells in the middle but tapers to almost a pointed base. It has a mysterious beauty.

John Takehara's globular form, called "Akebono" is another example of the power of classical shapes. The copper-red color comes about in the kiln's reduction atmosphere. Herman points out that the ox-blood color was highly prized in ancient China.

Hiroshi Sueyoshi covered a vase with small, iridescent oyster-like shapes.

Toshiko Takaezu's six-windowed form, enclosed in acrylic, has gold, grape and brown colors on a perfect small apple shape.

James Gorman made a big round green bowl with deep slashes for pattern.

Thomas Hoadley's brown Florentine bowl is made with a process called nerikomi , scraping and sanding slices of colored clay.

Edward O'rielly's "Landscape Vase" has bands of color suggesting seas, Sally Bowen Prange's "Edge-Scape Vessel" is a bowl with a strange edge that looks as though hunks had been bitten out on one side and pasted on the other. The white color with dark shadings is pleasant.

One of the few amusing pop or funky pieces in the show is Charles Fager's witty "Thinking About Self Portraints." A porcelain head with goggles and a beard swings open to show a series of heads in different positions. The head recalls Robert Arneson's masterful self-portraits, through it's not the equal.

Mona Brooks' 5-by-6 by-8-inch "Motorcar" piled with unhappy-looking people and happy-looking animals appeals to some. I think it's silly.

William Wilhemi "Cowboy Boots" with stars, clouds, cactus and gold boot tips and heels deserves a good kick.

Laura Wilensky's "Art Nouveau Jar" interrupts what started out to be a pleasant enough object to slice away the center and insert a stupid, unpleasant-looking figure.

Frank Fleming's "Desert Landscape" is an arrangement (14 1/2 by 30 by 21 inches) of a porcelain camel, a penguin, a bird and a chair, for no obvious purpose.

Clayton Bailey's "Toilet Teapot" is obscene.

Decorative objects and even sculpture should be beautiful, functional or funny. Those that are not are a waste of good clay. Still, the Renwick show has enough that are pleasing to encourage the belief that American porcelain makers are alive and active.