How Bottles were made

The process of making bottles has evolved over the years. Understanding the time line, evolution and associated tooling marks allows for easy identification of antique bottles. Glass is basically made from a mixture of sand, soda, lime and heat. The earliest Free Blown glass was usually dark green or more commonly called Black Glass. These European style bottles derived their color from iron which was mixed into the raw materials. Bottles have been made in America since the earliest settlers in Jamestown in 1608. These bottles were hand blown, just like European Black Glass and the earliest Roman glass which dates back to the 1st century B.C. The early glasshouse in Jamestown was not very successful and only produced bottles for a few years. The first truly successful glasshouse in America opened in New Jersey in 1739. Since that time bottle manufacturing has evolved steadily.

We can use this evolution and the tell tale marks associated with each new method to estimate the age of bottles we find. The first bottles ever made were hand blown without a mold. This process is called Free Blown. Free blown bottles were made one at a time in a very time consuming fashion. Because they were hand blown without a mold have no mold seam marks. These early bottles may however have other manufacturing marks that can lead us to identifying them. In order to remove Free Blown bottles from the blowpipe, a separate metal rod topped with hot glass was attached to the bottles base. When this rod was later broken off it left a distinct pontil mark. In order to produce more uniform shapes an ever evolving variety of molds were created. Bottles hand blown in a mold are called Blown in Mold (BIM). The earliest of these was the dip mold which was used to create a bottles body and left almost no identifiable mold seam markings on the bottle. Wood molds were used before cast iron molds were developed in the mid 1800’s. The wood was kept moistened in an effort to prevent the hot molten glass from charring the wood but still typically only lasted for 1000 casting. Some bottles made in wood molds will actually show the wood whittle marks. Hinged molds of various height and design were later developed which all left identifiable seam marks. Most of these were two part molds but some used three part molds and others had distinctive bottom hinge seams all of which can be helpful in the identification process. The majority of these blown-in-mold (BIM) bottles were finished with an applied top. Basically a blob of glass was applied after the body of the bottle was blown in the mold. An additional innovation was special tooling which allowed the applied tops to be sculptured to more uniform designs.

These tops are called hand tooled or hand finished tops. The basic evolution of glass making and development of molds is important to remember because it allows us to understand why some older bottles’ seam marks end before the top and other younger bottles which were made in full height molds have side seams which run to the top or even over the lip. For most blown in a mold bottles the rule is that the side seam can often be used as a gauge to the bottles age “ the further down the side the seam ends, the older the bottle”
 

During the proliferation of Mold Blown bottles Slug Plates were developed. A Slug Plate is a reverse embossed metal plate which is inserted into a two or three piece mold. They allowed smaller manufacturers and local businesses to emboss their own logo on a plate which would be interchanged in a standard bottle mold. The result would be individualized product branding without the expense of creating a unique mold.

In the early 1900s Michael Owens invented the automatic bottle machine. This invention revolutionized the industry. The 1903 version of his machine could produce 13,000 bottles per day. By 1909 improvements allowed the machine to make even small thin glass medicine bottles. One of these machines could make over 30,000 per day. By 1917 an automatic machine could spit out over 60,000 bottles per day, which made bottles much more affordable to the masses. All bottles made by machine are referred to as Automatic Bottle Machine or ABM.

The most common color of early glass made in the United States was green or light blue in variations of shades. This early glass is called Aqua glass. Clear glass was much more expensive to produce because glass blowers had to pay for more purified materials. It was later learned that a variety of compounds could be added to the basic mix to obtain other colors such as amber, cobalt blues and reds.

Around the turn of the century, the typical color of glass used for bottles changed from aqua to clear. Fewer bottles were being embossed with unique individual manufacturers logos and by the late 1930's painted label bottles became more cost effective to produce. Bottles lost their individuality as technology improved.

Knowing the techniques of glassblowing, including how to identify free blown, mold blown and automatic machine made bottles and the unique manufacturing marks each process leaves on the finished product is the key to estimate a bottles age. Please refer to this texts bottle mold seam and time line diagrams for a visual reference of each style mold and associated identifying manufacturing marks.