Red Sea Glass
By Rebecca Ruger
You've probably heard the myth or a variation of the tale of how red glass was discovered-that a nobleman inadvertently dropped his gold ring or a gold sovereign into a vat of molten glass and the glass turned red. While it's always interesting to hear tales of so-called "accidental discoveries," this one is untrue. Experiments have revealed that this would likely result only in a puddle of melted gold at the bottom of the vat.
Red glass of some sort has been produced almost since the time that glassmaking began. Knowledge and know-how of producing gold-ruby glass has been lost and found over many centuries. An early innovation of red glass can be found in the fourth century Lycurgus cup, which is exhibited at the British Museum of London. The cup shows a jade green color when lit from the outside but a deep ruby red when illuminated from the inside. It was found to contain minute amounts of gold.
Sixteen of the 133 chapters of Antonio Neri's L'Arte vetraria (The Art of Glass) published way back in 1612 in Florence, Italy are devoted to the making of red glass. They describe using manganese and copper to make red, and one 'recipe' does tell of the use of gold. Red glass made from gold is not an easy process. The gold must be made into a colloid by dissolving gold in a solution of nitric acid and hydrochloric acid (aqua regia). The color will not appear until the glass is reheated to over 1,000 degrees. This process is called "striking" the glass. Tin was often added, possibly acting both as a reducing agent and in order to increase the solubility of gold in the melt.
Different elements added to the basic glass recipe will produce different shades or variations of red. Adding pure, metallic copper makes a very dark red which is what we know as today's ruby colored glass. Smaller concentrations of the aforementioned gold chloride will yield a less intense red, sometimes called cranberry red.
Selenium was another metal used to color glass red. In an article from the Journal of the American Ceramic Society, from 1919, F.A. Kirkpatrick and George G. Roberts wrote, "As a coloring agent selenium has certain advantages over copper and gold. It is a cheaper coloring agent than gold. With proper manipulation selenium always gives the desired color while copper-red glass frequently comes from the pot spangled and spotted."
Gold ruby glass saw its peak in Europe in the late 17th century, and it's been said that every central European king owned gold ruby glass vessels of some kind. Ruby glass (not made from gold) was a popular Victorian color that set many a table. In the 20th century, red depression glass, red glass kitchenware, and red elegance glass saw their own fashionable periods. Avon even produced a dinnerware line-the 1876 Cape Cod Collection-in the 1970s, which saw great popularity and remains a collector favorite.
If you're finding red glass on the beach (lucky!) it can have many origins, some stated above. Other sources can include red tail lights from when they were still made from glass, glass insulators (one of the rarer insulator colors), ship's lanterns, the sea glass collector's favorite Schlitz ruby red bottle, Fenton's red hobnail glass, wine bottles, carnival glass, decanters, perfume bottles, art glass, and inkwells.
Watch videos about all the colors of sea and beach glass
This article appeared in the Glassing Magazine November 2017 issue.
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