The Evolution of Glass

Most of us are aware that glass has been produced since ancient times. The first glass vessels date from around 1500 B.C. but it wasn’t until around 30 B.C. that the Romans invented the blowpipe which allowed molten glass to be blown and spun into thin sections. Manufacture of colorful glass for use in churches and cathedrals reached a high art in Europe during the middle ages.

While glass has been around for thousands of years, the availability of clear glass for use by the masses is actually a relatively recent development. The first glass making plant in the United States was built in Jamestown, Virginal around 1610 but failed within a year. Other attempts at glass making likewise failed. It wasn’t until 1739 that a successful glass works was established in the U.S. The plant was built by Caspar Wistar in Salem County, New Jersey. It operated until around 1780.

Early glass making efforts were dedicated to making containers for food, medicines and liquor. Sheet glass such as is used in windows (and clocks) was not readily available from American manufacturers until the early 1800’s. Glass at this time was created by attaching a molten lump of glass to a blowpipe then blowing a bubble into the lump.

The white-hot lump of molten glass was then spun rapidly and expanded outward to create a thin round sheet. As a result of the technique, the final sheet always had a rise or “crown” in the center where the blowpipe was attached. This glass making technique was therefore called crown glass. Usually, pane-sized squares or diamonds were cut from the sheet and the center crown reprocessed. Sometimes, thrifty shoppers could purchase the center “crowned” portion of the glass at a low price for use in windows. These are seen from time to time in old houses.

By about 1825 the crown glass process was replaced by a technique in which the lump of molten glass was blown into a long cylinder. Once the cylinder had cooled it was sliced down one side and then reheated. When heated the cylinder unrolled into a flat plate of thin, clear glass which could easily be cut into window pane sizes with little waste. Cylinder glass marked the point at which glass could be produced at prices that the masses could readily afford. Cylinder glass was the prevalent technique used in the United States from around 1825 until about 1903.

 Cylinder glass making was a radical breakthrough in the production of low cost window glass. It was, however less perfect and transparent than modern glass. Because the glass cylinder from which the flat panes were eventually cut was blown and not pressed there were small variations in thickness from one area to the next. This produces the small “waves” often seen in the glass. Additionally, the melting and mixing process used with early glass was less efficient than modern glassmaking. As a result, air pockets were not thoroughly removed from the molten glass and tiny bubbles or “pearls” are usually apparent in the finished plates.

Glass making in the 1800’s was less efficient and perfect than found today. This however is the quality that distinguishes true antique glass from its modern counterpart. Viewing antique glass from a slight angle so that a reflection can be seen will quickly reveal the uneven surface. Modern glass, on the other hand, will look perfectly flat and smooth when viewed in the same manner.

 Another tale-tale sign of antique glass is the presence of many tiny air bubbles trapped in the glass.

All glass up to the introduction of modern pressed-glass techniques (1903) will have these tiny bubbles.

Colored Tablets

From the early 1800’s on colorful tablets were produced using a variety of techniques. The three most common techniques for creating colored tablets are presented here.

 Stencils: The use of stencils to repeat patterns dates far into antiquity. Earliest use of stencil use can be found in cave paintings dating to 30,000 B.C. Ancient Egypt use stencils extensively in tomb decorations and ancient Greeks created mosaic designs using stencils. The word stencil comes from the middle-English word “stanselen” which means “To ornament with sparkle” and the earlier Latin “stansel” which means “spark”.

American colonist, unable to obtain or afford expensive wallpaper or decorated furniture from Europe, used stencils to decorate both. From about 1760 until 1840 artist traveled from town to town and applied stenciled designs to furniture, walls and mantles. One of the most prolific of these was Moses Eaton jr. (1796-1886) who created stencils in hundreds of homes in New England in the 1840’s.

Stencils grew in use as the brass movement came into use and clock production skyrocketed. Early designs tended to be bold geometric designs but very intricate and complex designs soon followed. Bright colors as well as gold pigments were combined to produce rich sophisticated tablets that contributed greatly to the style of clocks of the period.

The most notable creator of stencil designs for clock tablets was William B. Fenn of Plymouth, Connecticut (1813~1890).  Fenn worked for Seth Thomas between around 1830 and 1840 then started his own business supplying clock tablets to Connecticut clock manufacturers. Between 1840 and 1864 Fenn was a major supplier of clock tablets to manufacturers such as Seth Thomas, Silas Hoadley, Brewster & Ingraham, Birge & Fuller as well as many others.

Many of Fenn’s most successful stencil designs have been published by the American Clock & Watch Museum in two books Clock Decorating Stencils (ISBN 0-930476-17-4) and More Clock Decorating Stencils (ISBN PUB259) Original Fenn stencils, acquired from the family, were used to produce the photos in both books. These books are a fantastic and historically correct reference to stencils of the period.

Litho-Paper Process:  In the 1830’s an image transfer process was developed wherein designs were created on metal plates by engravers. The engraver was able to achieve a level of detail not possible using stencils or other means.

The engraved plate was used to print the design in black ink onto very thin paper. Size or varnish was applied to the glass then the paper was pressed onto the size once it reached a light tack. The paper and size were then allowed to cure.

Once cured, the paper was moistened with water and gently rubbed off leaving the inked design embedded in the varnish on the glass.

There were several advantages to the litho-paper process. One: As noted, extremely fine detail could be produced by the engraver. Two: It could be inexpensively repeated on clock tablets. Three: Once the black image outline was applied, colored paints could be quickly added by non-artist workers to complete the tablet.

 With clock production volumes growing, litho-paper tablets provided a means to produce a high quality tablet image with a minimum of cost and effort.

The inks and/or varnishes used in the process were chemically unstable and flaking was common problem. Few good examples of this process have survived.

Fortunately, there are ways to reproduce high quality litho-paper tablets using commonly available materials. Many good images still exist and these can be used as a resource for recreating a needed tablet design.

Direct Printing to Glass: At some point in the 1840’s a new process for decorating tablets was developed wherein a design was printed directly onto the tablet glass which had been prepared with a coat of varnish.

Like litho-paper, the direct-to-glass process used finely detailed engraved plates as the master for the design. Unlike litho-paper, this process appears to have been quite stable with many examples surviving today. By the mid 1860’s stenciled tablets were almost completely displaced by this new, lower cost process.

The direct-to-glass process has, from time to time, been referred to as a “Decalcomania” process. The term Decalcomania comes from the French for "tracing craze". 

It was a practice of transferring colored designs to the skin from damp paper. This fad reached its peak in France in the mid-1800’s so the comparison of it to the direct-to-glass printing process is understandable.

Tablets produced using this process are identifiable in several ways. First, the designs are generally more finely detailed than those achieved with stencils. Gold detail lines can be quite thin due to the precision that can be achieved by the original engraver. Detail lines on stenciled tablets tend to be wider. Secondly, the detail achieved with an engraved block is usually much greater than can be cut into a paper stencil. Scenes depicted using the direct-to-glass process can be quite complex. 

Finally, when paint is lost on a tablet produced using this process the actual design can usually still be seen imprinted into the underlying size on the tablet.

Repair of the fine-line detail on a decalcomania tablet can be quite challenging, but there are several modern methods that can be used to make repairs or completely recreate a missing or broken tablet.

Digital restoration of tablet images can be used to create patterns or even water-transfer decals that can be transferred to correct antique glass then backed with with a coat of paint in the correct color. The results possible using this and similar techniques are quite good.

Chapter 10 of Extreme Restoration dedicates around 80 pages to detailing the various techniques used to decorate glass tablets on antique clocks. Repair as well as re-creation techniques are explained and supported by many, many photos.