Glass has been appreciated for its beauty for centuries, but not until recently has it been so generously used as structural elements in office and home interiors. No longer relegated to simple decorative windows or shower doors, contemporary glass techniques are allowing architects and designers to transform environments in startling new ways.

"Glass opens up whatever space you have," said Michael Asselmann, president and founder of San Marcos-based Cast Glass Images, a small independent manufacturer of architectural glass. "It has always been a real fascinating material, and I don't think we have scratched the surface of what can be done with it."

Asselmann, who started experimenting with glass in 1978 as an art student in Dortmund, Germany, began Michael's Art Studio in 1982, a small 1,000-square-foot studio on Twin Oaks Valley Road in San Marcos. From there, the name was changed to Cast Glass Images. The business was incorporated and moved to a larger space on Enterprise Way in San Marcos. And finally in 2004, they settled in the current 8,000-square-foot factory on Armorlite Avenue in San Marcos.

"We are working on some big, exciting projects that I can't tell you about yet, but one is in Las Vegas," said Asselmann.

Right now the company is working on 60 interior doors for a condominium project in downtown San Diego.

One of Asselmann's designs is a large shower enclosure -- in aqua tones with a palm design -- for Sheryl Straight's master bath in Carlsbad.

"We live with an ocean view, so it complements the view back there," she said. "We were so happy with the work they did -- I think it added twice the value to the house than what it cost us."

Straight said she heard about the company because the Asselmanns are regular customers at their UPS store. "We got the brochure a couple of years ago, and when we bought a new house in Carlsbad, we knew just who to call."

Asselmann recently brought his wife, Kelly, into the business to help run office production and with sales and marketing. Prices start at about a couple of thousand dollars for an interior door and go up from there.

And, if profits -- from about $700,000 in 2006 to more than $1 million last year -- are any indication, Cast Glass Images certainly seems ready to take advantage of the growing trend in architectural glass.

"You really can't do this with any other medium," Asselmann said of the countless applications of his custom glass -- from windows and partitions, to entryways, frameless shower and bath enclosures, tables, countertops and tables.

"People are always underestimating how strong glass is. Look at the new headquarters of the MacIntosh building in New York. It's all glass, the stair treads and everything. This is why glass is becoming such an important architectural application. You can create whole walls from it, and it's energy efficient, too," he said, adding that he has read about homes made of 80 percent glass that keep the heat inside in winter while staying cool in summer.

Asselmann admits the name of his company is a bit of a misnomer, as most of the architectural glass his company produces is either etched tempered glass or slumped glass, created by heating sheets of glass in a kiln until it conforms to the shape of a form or mold. Cast glass is typically made by pouring molten glass into a mold and cannot be tempered.

At the manufacturing facility in San Marcos, Asselmann and his artists work closely with clients (architects, interior designers, home builders or homeowners) from early concept to final design. For slumped glass projects, Asselmann and his team work from scale drawings to hand-carve a mold with the glass's final design.

"The mold is the most expensive part," explained Asselmann, who was reluctant to mention the exact kind of porcelain fiber material used, saying only that it is the same used for the heat shield of the space shuttle.

The firing process, which takes between 12 and 14 hours, is constantly monitored; any dramatic change in heat and pressure can result in disaster. "I have spent six figures in sleepless nights," said Asselmann of the learning process that, for him, has spanned decades.

Once the glass is annealed (cooled) and meets Asselmann's high standards, the architectural glass is sent to a special factory in Ontario, Calif., for tempering.

Tempered glass is one of two kinds of safety glass regularly used in spaces where standard glass could pose a hazard. Four to five times stronger than standard glass, it may break in a severe earthquake, but it will break into small dull fragments instead of large, dangerous shards.

"In an earthquake like that," said Asselmann, "the glass is the least thing you'll have to worry about."

At the Ontario facility, "the glass goes through a conveyor system and is coated with silicone with rollers heated to 1,200 degrees Fahrenheit," explained Asselmann. "Then when it comes out, a shell is formed on the glass, and you can't break it even if you hit it straight with a hammer. You can't cut it or break it, and it has a temper bug stamped on the glass, which tells the inspectors it is to code."

Asselmann and his team of four other employees at Cast Glass Images also do detail etchings and handcrafted frosting on tempered glass. They offer airbrushing and deeper carvings on annealed glass that can also be hand-painted for a touch of color. All carved applications can be made on plain glass, colored glass or in combination with slumped glass.

The team can create designs using standard textures or they can create completely custom designs, such as arching dolphins or a beach at high tide. "I don't want it to look like something from Disneyland," said Asselmann of his handcrafted designs of marine life, which are particularly popular with customers.

Cast Glass Images also is starting to use large or powdered colored frits (a partly fused mixture of sand and metallic materials), which are fused between two layers of glass in the kiln to create more colorful options.

"We pride ourselves on our emphasis on detail," said Asselmann. "We give you more bang for your buck because we can create more than one design detail for no extra charge."

Contact staff writer Ruth Marvin Webster at (760) 740-3527 or rwebster@nctimes.com.

Cast Glass Images Inc.

850 Armorlite Drive

San Marcos, CA 92069

(760) 744-7082

www.castglassimages.com