Early Bottle Manufacturing Tools & Technology
(First published in earlier editions of the Bottle Muse)
Around 1800, most bottle molds were made of clay or wood, and formed only the base and body of the container. The neck had to be drawn out utilizing the skill of the glassblower. Shortly after, two piece hinged molds, forming all but the bottle’s neck became common. Unless “fire polished”, or blown in “paste molds”, the bottle produced in hinged molds exhibit seam marks where the two pieces of the mold came together. “Fire polishing ” involved returning the bottle to the intense heat of the furnace just long enough to melt away any defects or marks on the surface of the glass. A “paste mold” was a metal mold which was coated with carbon, and then sprinkled with water or oil before each blowing. This lubricated the mold allowing the blower to slowly turn the bottle in the mold as he blew, eliminating seam marks. These are sometimes referred to as “turn mold bottles”.
As early as 1820, three and four piece molds were in use. Molds made of hard woods quickly burned away with repeated use, in spite of the fact that they were dipped in water before each blowing. Longer lasting brass, copper, and cast iron were used with increased frequency during the 19th century. Being the least expensive, cast iron was commonly used for bottles, while the use of brass and copper molds were usually reserved for making the more expensive table ware. “Chilled Iron” molds were introduced immediately after the Civil War and produced a smoother surface which did not require fire polishing. Regardless of the mold type, most early bottles had lips which were formed by hand tools. In the case of the “blob top” bottles, the body of the bottle was cut from the blow pipe with shears, and an additional piece of hot glass was placed around the neck to form a crude lip.
The “pontil rod” was an iron rod which was used as a holding device by placing a small amount of hot glass on the end, and placing it on the bottom of the (still hot) glass bottle. The temperature of the glass had to remain between 1,500 and 1,700 degrees Fahrenheit while being worked. Once fastened on the end of the pontil rod, the bottle could be cut from the end of the blowpipe with shears, and the lip formed. Once the bottle was completed, the pontil rod was broken away, creating a distinctive mark, or scar. This undesirable scar was eventually eliminated with the development of the “snap case” between 1850 and 1860. The snap case had a smooth platform bottom, and spring loaded arms which fit over the shoulder of the bottle, giving a more finished appearance to the completed bottle.
Around 1850, a process called “bursting off” was developed. In this process, the glassblower continued to blow after the bottle or jar had been formed in the mold, creating a glass bubble above the top of the mold. When the glass bubble burst, the container was removed from the mold and after annealing, the top rim was ground until smooth. In this manner, the threads to accommodate a screw cap could be included in the mold.
Mason’s patent for present style screw-top fruit jars was issued on November 30, 1858. The Owens automatic bottle making machine was not patented until 1903. The presence or height of a seam mark on a bottle is not definitive indication of its age, or whether or not the bottle is blown or machine made, and neither is the fact that the bottle has a screw cap for a closure. It is risky to rely on generalities. There is no substitute for knowledge through research.
The majority of melting furnaces in this country burned wood until about the middle of the 19th century, and annealing ovens until much later. Although the first American glasshouse to use soft coal was built by Isaac Craig and James O’Hara at Pittsburgh in 1796-17997, none of the factories outside that area used it until 1810. Bituminous coal became available with the opening of the Virginia & Cumberland mines. In some places, anthracite was also in use during the 1850’s. Glassworks in South Jersey burned chiefly wood until after 1855, when they began to use anthracite. By 1860, only one furnace in New England continued to burn wood. By 1880 the fuel used in glass making in the United State was chiefly coal.