In the early 20th century, changes in manufacturing processes, as well as more pure batch materials, dictated different ways to decolorize glass, and the use of manganese oxide for this purpose dwindled.
If they set glass out and it turned purple, it proved to them and to their customers that the glass was, indeed, made prior to ca. 1915 when most, but not all, glass companies ceased using manganese and substituted selenium as the clearing agent.
true bright pink, like true bright purple, are ultra rare. Most purple sea glass is actually “sun” purple – in the old days manganese was added to glass as a clarifying agent, and manganese turns purple when exposed to UV rays – like those in sunlight.
Manganese-decolored glass that has undergone a color change due to exposure to the ultraviolet rays of the sun is variously known as sun- colored amethyst (SCA), solarized amethyst, solarized purple, or irradiated glass.
Historically, for African Americans, the purple glass is a symbol of burials in African American cemeteries. You carry a purple vessel with water in it and smash the glass vessel on a tombstone.
True purple glass is much rarer. In our English Sea Glass collection, it averages one in 5000 pieces as true lavender glass was reserved for the Monarchy (showing Royalty) and for the Bishops in the church. Light Blue or Cornflower Blue (Pre 1900 Phillips MOM bottles, Bromo Seltzer, Vick's Vapor Rub, etc.)
In the early 20th century, changes in manufacturing processes, as well as more pure batch materials, dictated different ways to decolorize glass, and the use of manganese oxide for this purpose dwindled.
Some of the more valuable colors are cherry red, black amethyst, and ice green. Take note of the iridescent quality of the antique glass to be sure there are no worn or uneven sections.
Glass that contains manganese will turn lavender when exposed to UV light over time. When I say time, I mean years of exposure to sunlight. Because it takes so long, some people expose the glass to UVC lamps in a box at high intensity for 3–4 weeks to get them to change from clear to lavender.
Red sea glass is widely regarded as the rarest of them all. The scarcity can be traced back to the past when production of red glass was not as high as the other colors. Red glass was typically used in limited quantities for specialty items such as warning lights, lanterns, or decorative glassware.
Tyrian purple: The lost ancient pigment that was more valuable than gold. For millennia, Tyrian purple was the most valuable colour on the planet.
Manganese is one of the oldest glass additives, and purple manganese glass was used since early Egyptian history. Manganese dioxide, which is black, is used to remove the green color from the glass; in a very slow process this is converted to sodium permanganate, a dark purple compound.
Because of the age of the glass, the small subset of glass products which used this production technique, and the need for extended exposure to the sun's light, Purple Sun Colored Antique Glass is a rare and collectible artifact, and fascinating piece of industrial history. Today the supply is extremely limited.
Bottles made from glass with just the basic ingredients (sand, soda & lime) will usually be different shades of green because of the iron impurities in the sand, though other colors can also be attained depending on many factors.
From 1885 to 1914, manganese dioxide was used as a clearing agent by glass makers to make sure the glass remained clear. However, when exposed to the sun over time, the manganese dioxide in the glass will cause the glass to turn a purple tint. The main source of this clearing agent was Germany.
Purple or as you will hear often, 'Amethyst' glass, was given its color by adding manganese oxide to a molten glass mixture of sand, potash and lime. Purple or Amethyst glass should not be confused with clear antique glass that has changed color due to sun exposure (see picture to left).
During the mid and later 1800s virtually all American glass companies were using manganese in their glass formula. Around 1915 the use of manganese was discontinued and selenium became the chemical of choice as a clarifying & stabilizing agent.
Vintage glass that contains manganese is known for its pink or purple hue when exposed to UV light. Manganese was commonly used as a decolorizer in glass production, and its presence results in a distinct response to UV rays.
Color and pattern, which helps identify both the rareness of the piece as well as its manufacturer. Some of the most valuable colors are cherry red, black amethyst, and ice green.
It fell out of style over the decades, but now, mercury glass has made yet another comeback, especially among antique enthusiasts. Today's version isn't made with mercury or silver. Instead, a silvering formula applied between double-walled glass creates a dull mirror finish.
The auction record is £;520,000 ($1,078,480) for a Roman glass cage-cup of c.AD 300, known as the `Constable-Maxwell cage-cup', measuring 17 cm (7 in) in diameter and 10 cm (4 in) in height, sold at Sotheby's, London, UK on 4 June 1979 to Robin Symes (UK) of the British Rail Pension Fund.
Neodymium Glass (365nm / 395nm)
Neodymium glass (sometimes referred to as Alexandrite glass), changes color according to different lighting conditions. The glass appears lilac (or sometimes pink) in natural sunlight or yellow incandescent light, and smoky blue in fluorescent/white light.
Children and adults who drink water with high levels of manganese for a long time may have problems with memory, attention, and motor skills. Infants (babies under one year old) may develop learning and behavior problems if they drink water with too much manganese in it.
Even today, so-called “Rosaline glassware” is still made in acrylic glass production. Selenium is also used to color church windows and light-absorbing “privacy glass” (such as tinted windows in cars).