In 1915, chemists at Corning Glass Works in Corning, New York, created a special borosilicate glass that was resistant to thermal expansion and contractions. This new glass—branded as “Pyrex”—held up under quick, extreme temperature changes, which made it ideal for railroad lamps, scientific experiments, and, of course, cooking. Beginning in 1921, a company called Joblings produced Pyrex under license from Corning in Great Britain and Australia. Corning’s first line of clear-glass Pyrex Ovenware debuted in 1915, featuring 12 pieces such as casseroles, custard cups, a bread pan, pie plates, and shirred egg dishes. Early Pyrex was cloudy, and the word “Pyrex” can usually be found on the base of the piece. This cookware was an immediate success with homemakers who’d previously cooked in metal pans and earthenware. For the first time, they could bake, serve, and store their food in the same dish. Collectors, however, are most attracted to the colorful vintage Pyrex products that were introduced in 1947 and produced until the late '60s. To create even more durable dinnerware for the military during World War II, Corning came up with an even stronger version of Pyrex, this time made with a soda-lime composition instead of borosilicate. Advertising crowed that Pyrex kitchenware was “Tough as nails and guaranteed!” Using its prewar molds, new Pyrex products were made out of opal or white glass, sprayed with a bright color, and then sometimes printed with an attractive pattern. Nested mixing bowls are among the most identifiable and beloved vintage Pyrex bowls. The first, and currently most popular set, is the solid “400 Multicolored Mixing Bowls,” also referred to as “Primary Mixing Bowls” or “Primary-Colored Mixing Bowls.” It includes a 4-quart yellow bowl (#404) with a 10-inch diameter, a 2.5-quart green bowl (#403) with a 8.5-inch diameter, a 1.25-quart red bowl (#402) with a 7-inch diameter, and a half-quart blue bowl (#401) with a 5.5-inch diameter. All vintage Pyrex mixing bowls come in these four sizes, but newer bowls have thinner walls. In 1949, the #404 bowl was also offered separately in red. In 1957, the 300 nesting bowl sets were introduced, and these only had the three smaller bowls. Ten years later, Pyrex debuted its currently popular “New Dot” pattern—white glass with three rows of dots in a single color—in a three-bowl nesting set, and each bowl had its own dot color: orange, red, and blue. A fourth 4-quart bowl with green dots was introduced in 1969, and it is the most valuable of the set. Cinderella bowls, or mixing bowls with two pour-spout handles, were introduced in 1958. Casseroles were made in similar colors and patterns as the mixing bowls starting in the late '40s. Many were offered as one-off promotional items or Christmas specials. Others were a part of huge kitchenware sets, so that a homemaker could fill her kitchen with matching Pyrex patterns. Casserole lids came with or without knobs, in clear and colored glass, and with or without printed or engraved patterns. Lids without top knobs doubled as trivets. In 1956, 2-quart casseroles were offered with “Jetsons”-esque candle warmers. Two years later, the Cinderella casserole handles made pouring easier. Refrigerator sets, billed as “oven-refrigerator sets,” are also prized by collectors. The concept began in 1925, with squared-off, stackable clear Pyrex containers that saved space in the icebox. In 1949, a refrigerator set was issued in three of the colors of the first 400 bowls. The yellow was the 1.5-quart size, blue was 1.5 pints, and red was 1.5 cups. The original clear lids had fine ribs that tend to collect dirt. These sets were made in clear again from 1950 to 1952, and then in the popular Pyrex patterns of the day. Other postwar Pyrex products include Chip and Dip sets, Hostess casseroles (large bowls with lids), bowls sold with Hamilton electric mixers, cake dishes, clear canisters like cracker barrels and cookie jars, clear or patterned carafes and pitchers, butter dishes, divided dishes, salad sets, and shakers. The company also offered white dinnerware rimmed in colors like dove gray, turquoise, lime, and flamingo, available with an optional 22-carat gold trim. The regency green and royal burgundy colors were added later, and these are the most rare. Divided plates for children were also produced. Generally, the patterns of mixing bowls, casseroles, refrigerator sets, and other items that come in the bright, cheerful colors of the 1950s, such as pink and turquoise, are far more popular with modern Pyrex collectors than the homey, muted earth-toned patterns that sold well in the '60s. For example, the 1959 “Butterprint” pattern—depicting an Amish farming couple surrounded by wheat sheaves, roosters, and corn stalks—also called “Amish,” “Farmer & Wife,” “Buttercup,” and “Rooster & Corn,” sells well now, because it is most often found in vibrant turquoise-on-white or white-on-turquoise. In contrast, the “Early American” pattern of the '60s—which portrays bald eagles, oil lamps, tea kettles, salt-and-pepper shakers, corn husks, antique coffee grinders, tabby cats, and weathervane roosters—comes in shades of brown or gold-on-brown that don’t appeal to current collectors. This pattern, also known as “Early American Heritage, “Country Pictures,” or “Weathervane” usually sells for much less than “Butterprint.” Some sellers label this line as “Americana,” but it is a mistake. Pyrex patterns that are popular with collectors include “Gooseberry” (particularly in pink), “Rainbow Striped,” “New Dot,” “Terra,” “Snowflakes” (in turquoise and charcoal), “Snowflake Blue,” “Daisy” (designed to satisfy the era’s craze for yellow), and a rare promotional pattern known as “Balloons,” as well as an Atomic Age “Eye” pattern seen only in a two-bowl Chips and Dip set. Other well-known earth-tone '60s patterns include “Gold Acorn,” the floral “Spring Blossom Green,” or “Crazy Daisy,” and the simple wheat sheaves of “Autumn Harvest.” Of course, condition of the color and pattern will affect the value of the item. A common Corning pattern known as “Cornflower Blue” appears on casseroles, teapots, and myriad other kitchenware items, but collectors should note that none of these are known to be made of Pyrex glass. Pyrex’s 1966 real “Americana” bowls are also popular now. In stark contrast to “Early American,” these nesting bowls come in solid primary colors with a single white stripe on the rim. Collectors are also attracted to vintage Pyrex from the “Verde” line, which generally features solid-colored items in various shades of green. Before the '40s, clear Pyrex Ovenware, introduced in 1915, exploded in popularity. The plain 12-item line started with casseroles, custard cups, pie plates, bread pans, and shirred egg dishes. It quickly expanded to 100 unique items in 1922. (Pyrex introduced its first clear 2-quart mixing bowl in 1931, which led to the nesting sets a decade later.) In 1918, Pyrex began offering engraved-glass pieces with “Fern,” “Spray,” and “Key” designs. These were popular until the 1930s, and then were discontinued in the 1940s. Pyrex measuring cups, which like the first custard cups are still made today, are probably among the most iconic Pyrex products. The earliest, introduced in 1925, had two spouts, but it was quickly replaced a year later with a single-spout measuring cup. In 1941, Pyrex first made measuring cups with red-lettering, just like the measuring cups we know today. Only one modification was made in the 1990s: Modern cups have an open-bottomed handle, while earlier handles curve back into the cup. One of the most collectible measuring cups is a 1-quart size with a metal beater on the top. The company experimented with its Pyrex pie plates, too, issuing hexagonal pie plates between 1917 and 1938. Corning debuted the 10-inch “Flavor-Saver Pie Plate” in 1943 with fluted edged that promised to “keep all the juices and flavors in your pies.” Other Pyrex Ovenware items include au gratin dishes, cake dishes, platters, juicers, refrigerator sets, roasters, glass rolling pins, double-compartment baking dishes, bean pots, teapots (which could not withstand direct stovetop heat), pie birds, molds, trays, and utility dishes. A breakthrough in 1936 led to a new Pyrex glass dubbed Flameware that was tough enough to sit directly above the flame. The early Flameware can be identified by its bluish cast; it all became clear within 10 years. During that first decade, the maker’s mark was stamped in green ink and not molded into the glass. Hence, most of the marks have worn off of these early items. Flameware coffee makers are particularly collectible. They come in many varieties including the Drip Coffee Maker, the Instant Coffee Maker, the Percolator, and the Vacuum Coffee Maker. Silex company also sold many coffee makers using Pyrex glass. The Chemex Filter-Coffee Maker was a particularly attractive modern coffee carafe made out of a single piece of Pyrex. The first saucepans offered as Pyrex Flameware came with removable handles featuring a glass button inside a metal loop. In 1943, an all-glass removable handle was offered, which was replaced by an all-metal handle, and then a permanent glass handle in 1955. Removable wooden handles were sold with Pyrex saucepans and double boilers during World War II. Other Flameware products included tea kettles, teapots, and skillets. Pyrex Flameware was discontinued in 1979, and replaced with the clear brown-amber glass called Pyrex Fireside. Then in 1983, Corning released its clear orange-amber ceramic-glass cookware line branded as Visions. Both Fireside and Visions were produced in a clear cranberry color, as well. Besides cookware, Corning innovations in glass chemistry were used in glass insulators, thermometers, glass construction blocks, Thomas Edison’s first light-bulb blanks, telescopes, television tubes, optical glass, nursing bottles, Christmas tree ornaments, and laboratory tools such as beakers, Erlenmeyer flasks, bottles, and funnels.