The diamond was removed from the “old” mark (diamond superimposed over an “I” and an “O” or oval) beginning around 1954, although a few bottle molds apparently didn’t have the diamond eliminated (i.e., the mold re-engraved) until as late as the 1960s. “M in a circle” mark used by Maryland Glass Corporation. Take care, Mark reportedly used in the c. 1920s on machine-made bottles. Most of the bottles with these embossings probably date from the 1880s-1910s era. I’m not sure, but I have doubts it is a Hemingray product. Trademark used for borosilicate glass formula, used for laboratory glassware, chemical bottles, etc. Federal is well known for having made large quantities of so-called “Depression Glass” in the 1920s-1940s. I.G.CO.L…………..Ihmsen Glass Company, Limited, Pittsburgh, Pennsylvania (c.1876-1900). E. S. & Co……….Evans, Sell & Company, Pittsburgh, Pennsylvania (1873-1877). It has an L and a B on the bottom (L over the B with a line between the two and a dot in the middle of the line). You are referring to the “regular” patent numbers, also called “letters patent” or “utility patent” numbers. K.H.& G……………..Kearns, Herdman & Gorsuch, Zanesville, Ohio (1868-1885). I keep coming across the words Great American Classics. K B L T……………Kilner Bros. Limited, Thornhill Lees, West Yorkshire, England. Franklin Industrial Co. was formed to control a number of related small industries in the Massillon, Ohio area, including sand and gravel companies and the operation of the Warwick Glass Company, which was supposedly founded in 1901 by a Maria Warwick. I.B.& G.CO……..Indiana Bottle & Glass Company, Cicero, Indiana (1905-1909). I don’t know when Fairmount Glass switched over to machine-made production. Thanks, Bethany, Bethany, What a wealth of information. Found on tableware. See “K in a keystone”. ARCOROC – FRANCE – mark on base of small dessert bowl. (on the base of handblown bottles)……………….see, G.W. Jewel (Representation of a jewel/gem such as a cut diamond, photo shown at right)………………unknown meaning. Also see the, L G W………………Laurens Glass Works, Laurens, South Carolina  (1910-1996). A very rare fruit jar, a type apparently made to be used with a cork closure, is also known with this marking. Could this be a Hemingray? G.W. This trademark, according to U.S. Patent &  Trademark records, was first used in 1932, although the logo was shown in catalogs as early as 1927 according to researcher Marg Iwen. K B (something, maybe G, maybe