EXTREMELY RARE SIGNED PITTSBURGH ART NOUVEAU RED BENT SLAG GLASS LAMP – CIRCA 1910. The lamp measures approximately 28″ high to the top of the finial, 15 1/2″ wide across the face of the shade from one corner to the other and 7 1/2 wide at the base. Diagonally, the shade measures 22 across from one corner to the other. This PILABRASGO (abbreviation for the Pittsburgh Lamp Brass and Glass Company) Art Nouveau red bent slag glass lamp is extremely rare due to the color of the slag glass. You will be hard-pressed to find very many lamps with this red-orange color of glass. The reason for the rarity of the color of the glass comes down to the process of making this color of glass. Red glass is the most expensive color of glass for items made in this era because the process involved included adding gold oxide or chloride. For a deep ruby red the gold content is higher than for, say, a lighter cranberry color. Red and pink (cranberry). Glass is typically the most valuable because of the gold content, while blue (made using cobalt salts), green (uranium), and yellow or amber (sulphur) tend to command lower prices. Anchor Hocking pioneered the addition of copper to produce the rich tone. Today, art glass makers use cadmium and selenium to get that deep, rich glow. This lamp is signed on the underside PLBG & Co. Pittsburgh Lamp, Brass and Glass Company was founded by Nicholas Kopp in 1901. The company produced some of the world’s finest etched crystal and satin red glass lamps. The company went into bankruptcy in 1926, reorganized as Kopp Glass Inc. And continues to make a multitude of specialty lenses, filters and lights for a variety of industries.