rather obtain an imperfect product rather than a perfect, common product. Impurities in the glass can create amber swirls, milk swirls, graphite inclusions, and two or three-tone insulators. Foreign objects contained within the glass are known to be nails, pennies, and screws. Although glass insulators are the most popular for the majority of collectors, many people collect porcelain insulators as well. These also come in a variety of shapes, sizes, and colors. They are classified in the U and M systems, primarily developed by Elton Gish. Manufacturers One of the major U.S. manufacturers that produced glass insulators during the 19th century and early 20th century in the USA was Brookfield Glass Company. It can be assumed that Brookfield may have had poor quality control as their insulators seem to be found with the most imperfections, however, this could be disputed. Another major U.S. manufacturer that produced glass insulators was the Hemingray Glass Company. They were known for producing the most variety of colors. Some examples of colors that the company produced are yellow, golden yellow, butterscotch, glowing orange, amber, whiskey amber, "root beer" amber, orange-amber, red-amber, oxblood, green, lime green, sage green, depression green, emerald green, olive green, yellow-olive green, aqua, cornflower blue, electric blue, cobalt blue, sapphire blue, glowing peacock blue, and many others. Different colors were produced to allow two or more different utility companies to quickly identify which wires were theirs by the color of insulator if multiple wires were strung over the same utility pole. For example, one company may have a string of amber insulators, while another, on the same poles, might have their insulators in cobalt blue. There are many manufacturers in the United States, Canada, and other countries that can be found embossed on all styles of insulators. A non-comprehensive list of these manufacturers is below: United States AT&T American Insulator Company Armstrong Brookfield Glass Company Beaver Falls Glass Company Baltimore glass manufacturing company Barclay Birmingham Boston bottle works Buzby California California Electric Works Chambers Chester Chicago Insulating Company Duquesne Electrical Construction and Maintenance Company Emminger’s Gayner Greeley Gregory Good Hawley Homer Brooks Hamilton Hemingray Glass Company King City Glass Works (K.C.G.W.) Kerr Knowles Kimble Luther G. Tillotson & Company Lefferts Locke Lynchburg McLaughlin Maydwell McKee & Co. McMicking Mulford & Biddle New England Glass Manufacturing Company (N.E.G.M.Co.) National Insulator Company Oakman Manufacturing Company Ohio Valley Glass Company (O.V.G.Co.) Owens Illinois Paisley Pyrex