Silver overlay is an electroplated coating of silver on a non-conductive surface such as porcelain or glass. Most techniques used to create silver overlay involve the use of special flux which contains silver and turpentine oil. This is then painted on the glass ornament as a design. After the painting is complete, the entire ornament is fired under relatively low heat, it is then cleaned after being quenched and cooled, then it is placed in a solution of silver. A low voltage current is run through the solution and the silver binds in the design, creating a permanent fusion of the silver with the glass.
A much older technique of overlay, which was commonly used in the Indian subcontinent since ancient times, involves the use of a silver sheet wrapped around the ornament and then the design beaten onto the sheet or it may be burnished. This technique renders the design silhouetted against a dark backdrop and was commonly called the Aftabi design technique. This technique of overlay predates the technique that is common today, but without the use of electroplating, it was a time consuming and tedious process, which could only be accomplished by skilled artisans.
History
The history of who first devised the process is unknown. What is known is that from 1870 onwards, a number of patents were filed for the process. Although all patents appear after 1870, it has been suggested that the process may have been discovered earlier, and the patents claimed a short time afterwards. The most well known patent holders are Frederick Shirley from the United States of America, whose patent dates to 1879, Erard and Round who were under the auspices of Stevens & Williams Ltd. whose patent is from 1889, John Sharling also of the USA, whose patent is from 1893 and Friedrich Deusch, the German inventor whose name is most associated with silver overlay today, whose patented the process in 1895 and displayed his work in 1907 at an exhibition in Bordeaux.
Deusch returned to Schwäbisch Gmünd in southern Germany where, in 1912, he founded his firm Deusch & Co. Deusch continued exhibiting his wares and gained the Gold Medal at the 1913 World Exposition in Ghent, Belgium.
With his presence, Schwäbisch Gmünd became the center of German silver overlay production. Schwäbisch Gmünd (about 20,000 inhabitants in that time) had a long tradition since the 16th century in the art of artists working with gold and silver. A school for applied arts existed there from an early date, which became a school for the precious metal industry in 1907. In the 1920s almost 190 firms were involved in the precious metals industry. The presence of materials, artisans, and component suppliers in on place created an ideal environment for the industry to thrive.
After Deusch and Company, other firms specializing in silver overlay were founded. In particular, the firms of Friedrich Wilhelm Spahr and Alfred and Manfred Veyhl were established.
Parallel to the development of German silver overlay, silver overlay production was also initiated in the United States.
Technique
The specific feature of German silver overlay is the degree of purity – 925 for Sterling silver or 999 for fine silver. The quality of silver used for German overlay can be seen by identifying the impressed 1000 mark (usually on the base or side of an item). The purity and thickness of the silver overlay ensures the beauty of the item is maintained without any loss to the silver even after many years of cleaning. Although other kinds of silver, such as nickel silver, can be sued for silver overlay, the effect is not as vibrant.
Bohemian and Venetian Murano glass are often described as silver overlay, but the silver is so thin that it looks as though it has been painted onto the surface, producing a flat effect.
Friedrich Deusch invented a way to combine silver and a non-conductive surface such as porcelain or glass with galvanization. He achieved this with a special conductive fluid (a type of flux) which was fixed permanently on the prepared form. The particular objects (such as a vase) were first roughened by engraving or using hydrofluoric acid to etch a design. This implies that a very exact covering of the surfaces had to be achieved to prevent any damage to areas which were not to be overlaid. Maybe they used a masking lacquer which could withstand the following baking in the kiln which was used to fuse the flux with the surface of the item. The next step was to galvanize the item with the purest silver (1000).