Glass blocks -- those funny, thick hollow things once used by college students to hold up bookshelves or by builders to tack on the outside walls of bathrooms -- have suddenly become chic.

Although glass blcok was once both an interior finish and a building material, it disappeared when the Art Deco movement faded and when broad expanses of glass became fashionable. But the Art Deco revival and post-Modernism have put glass block in a new light.

"Post-modernism is pushing us toward creating separate rooms again -- a kind of reaction to the open plans that were so popular in the '60s and '70s," says interior designer Mary Drysdale. "Glass block is a perfect solution -- it allows us to divide spaces without sacrificing a feeling of openness."

When Drysdale first proposed using a glass-block wall to a client living in an expansive apartment in The Westbridge, the reaction was something like, "Are you kidding -- that's the stuff they put in bathrooms." But the client put his trust in Drysdale and now has a separate foyer, created by a glassblock wall with a built-in planter that pierces the wall at eye level and drips greenery on both sides of the wall.

Inside the apartment, the other side of the wall forms a backdrop to the bar. Drysdale aimed ceiling-mounted pinpoint lights at the rippled surface of the 8-by-8-inch glass blocks. "The client wanted a peaceful, serene apartment. This wall is the only sparkly, unexpected element," says Drysdale.

The home of Stephen and Jean Hersh in suburban Maryland, built in 1925, already had an addition with touches of glass block. But when Architect Robert Lewis of Lewis & Holt began work on the addition for use as a breakfast nook, he put in a curving glass-block wall that was rippled for the first five feet and then became clear to the ceiling. From the street at night, the room, lit from inside, resembles a spaceship.

Despite the ceramic tile floors and the hard glass wall, the atmosphere inside is warm and intimate, perhaps because the light is so diffuse. Says Holt, who along with his partner uses a lot of this material, "Glass block gives you an interesting play of light between translucent and transparent panels -- and in the case of the Hersh home, it enabled us to handle the gently curving wall easily."

Architects Don Little and Dennis F. Cross used glass block in a novel way in a small branch bank in Silver Spring. The two created a sawtooth line of tellers' windows set on a diagonal so that the row of tellers moves back, stairstep style, into the space. Instead of using traditional wood walls, the architects selected glass block to create walls between bank customers and tellers, who peer across oak shelves and through heavy acrylic safety shields. The dark green carpets make the room appear solid, in contrast to the wall, which almost seems to float. The translucent material gives the bank the security of a solid wall but an openness that a traditional wall could not achieve.

For years, the deco look was rejected by designers. But its legacy in architecture may well be in the revival of glass block today.