text: 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).
  It was very important to monitor items being overlaid with silver – waiting too long resulted in visible dark spots and slight roughness where the cathode or anode were fixed. The cathode and anode were used to charge the item electronically and this allowed the fusion of silver to the area painted with the silver flux. The thickness of silver desired on the finished item determined how long the item needed to be left in the silver bath; this could be more than 30 hours. Finally, if the masking lacquer (discussed earlier) did not burn in the kiln, it must have been removed later (probably with chemical fluids).
  When colored enamels were to be used on the finished product, they had to be fired prior to the final stage of the silver overlay process. Engraving the silver was the last, and sometimes most laborious, work; it was brought to the highest level by Friedrich Wilhelm Spahr and his workers.