Unique shell shape. golden ruby red glass drinking glass by the 17th century, the German alchemist, apothecary and glass blower Johann Kunkel had been acquired by the Rijksmuseum. The deep, intense red color was obtained by adding gold to glass, a method and recipe pioneered by Kunkel. It dates from around 1685, Kunkel’s first decade as a glassblower at the court of Frederick William I, Elector of Brandenburg. Only about 20 early gold ruby-red Kunkel glasswares are known, and the shape, style, and engraving of this calyx are unique among them.
The bowl is engraved with a scene of putti frolicking around the vines. The engraving is attributed to the glass engraver Gottfried Spiller (1663-1728), who engraved several gold ruby goblets. The glass is processed in such a way that it does not look like blown glass, but more like a cut stone. Thus, this object is in keeping with the traditions of the Kunstkamera, a collection that brought together remarkable objects from nature, science and art.
The fact that gold compounds added to glass can give shades of red has been known since antiquity. The German alchemist Andreas Libavius wrote in his seminal text Alchemy in 1597 that dissolved gold created a red tincture that could be used to make a “red crystal”. The first modern treatise on glass, written by Antonio Neri of Florence in 1612, also noted that gold could produce red glass, but neither ancient texts nor later books on chemistry contained any information about the process or even a basic recipe.
The first to record a functional method for making ruby red glass was the Bavarian chemist Johann Rudolf Glauber, who wrote in 1659 that gold could be dissolved in a solution of a tin compound and hydrochloric acid. The gold then precipitated out of solution as a purple powder, later called Cassius Purple, which could be added to glass to make it red.
Glauber’s experiments never involved the manufacture of ruby glass itself. It was Johann Knuckel, being an alchemist and glassblower, who perfected the recipe and process for creating glassware from gold and ruby. He published his own treatise on glassmaking and taught practical chemistry at the University of Wittenberg. In 1678, Prince Friedrich Wilhelm I, Elector of Brandenburg and Duke of Prussia, settled Knuckel on a secluded island near Potsdam with a glassworks where he could experiment and perfect his production of golden ruby glass away from the prying eyes of competitors.
He was a huge success and the luminous crimson glass he made was considered a new precious material and not just glass. Like the rubies themselves, Knuckel’s golden ruby glass was considered beneficial for health, especially for blood disorders. His work started the fashion for ruby red glass in the late 17th century. Every sovereign and ruler in every court in Europe vied for possession of the golden ruby vessel, including the King of Sweden, who poached the master from the elector in 1693 and gave him a title of nobility and estate. Johann von Löwenstern-Kunkel died in 1703, and with him died the heyday of the ruby glass craze.