While his Favrile shades were free-form and hand-blown, Tiffany's first leaded shades were geometric in design. Often, Tiffany craftsmen made these shades in diochric glass which appeared green in reflected light but orange in transmitted light.

He shifted to organic motifs in 1900, when Tiffany introduced the earliest model of the popular Dragonfly shade at the Paris Exposition. Large blue-bodied dragonflies with overlapping purple-striated-blue wings were imposed on a blue-green background mottled with yellow to suggest rippling water. The wings, themselves, were covered with a metal filigree to simulate the dragonfly’s veins, and its red eyes, which touched the shade’s lower edge, or apron, were made of glistening glass jewels. Clara Driscoll, who in 1904 earned a $10,000 annual salary, designed many of these shades.

Another category of Tiffany lamp was the domed shade, also known as the flowered cone. Many featured profuse floral patterns of flowers in mottled colored glass with stems made of granular glass. He also made flowered globes and shades with irregular lower borders.

Tiffany’s Wisteria lamps fell into the irregular upper and lower borders category. The multicolored Wisteria shades were remarkable not only for their superb naturalistic integration of vines and blossoms but as a complex technical achievement as well. The traditional straight edge of the opening at the top of the shade was replaced by an openwork crown cast in bronze which simulated the twisted branches of the vine. Wisteria clusters terminated in an irregular lower border of unopened blossoms. Each Wisteria lamp consisted of over a 1,000 pieces of glass. A typical model sold for $400 in 1906.

Except for special commissions, most Tiffany lamps were made in his Corona workshops. Once he approved the design, an artist prepared full-scale drawings. Colorists prepared a chromatic scheme and craftsmen selected and cut the glass, using a template to guide them. Then they glued thin strips of copper foil around the edges of the cut pieces, which they placed over the pattern outlined on a wooden mold. They carefully applied lead and copper electroplating around the glass pieces, making sure that they rounded the lines in an organic rather than a flat manner.

The subject of Tiffany's marks is complex and filled with misconceptions, elusive to even the seemingly well-informed. Tiffany's marks and marking systems changed over the years. Some are clear, but others are obscure. Pieces aren’t always signed or retain their original identification. Some have had unauthentic markings added. Original Tiffany lamps bear the company’s name and perhaps a reference number. Some have original paper labels. Shades were also marked with a bronze pad.

"A specific Tiffany signature can usually be found pressed into the metal rim of the lamp’s shade," said Kim Hewitt, restoration expert with the Queens Museum of Art, in Corona Park, Queens, New York. "He sometimes signed his lamps ‘Tiffany and Co.,’ cut from 1900 to 1910, he usually signed them Tiffany Studios."

According to Alastair Duncan, Tiffany lamp expert and author of a book about him, the most popular models include the Wisteria, a perennial favorite, as well as the Peony, another hugely popular model that was in production from 1904 to the late 1920s. "The Magnolia was considered the pre-eminent Tiffany lamp some 20-odd years ago," she said. "It’s a very large floor model. Then we moved to the spiders and the cobweb lamps with mosaic bases. At the moment, the Lotus has become the most popular, but there are only three known--two of them are in private collections and one in a museum."

Tiffany retired in 1918, but he kept a watchful eye on the company. Nash carried on the business, but his later work, fighting a rearguard action against Art Deco, wasn’t of the same quality. In 1928, L.C. Tiffany severed all connection with the firm, withdrawing permission to use his name.

By his vision and energy, Louis.C. Tiffany succeeded in blending classical motifs with bold new techniques in glassmaking to create a distinctive American art form. The demand for Tiffany lamps among today's collectors attests to the lasting value of his work.