What causes the varied purple hues in old glass bottles? (2024)

FAQs

What causes the varied purple hues in old glass bottles? ›

An interesting characteristic of colorless glasses which contain manganese dioxide as a decolorizer is their tendency to turn different shades of purple when exposed to the rays of the sun or to other ultra-violet sources. It is a photochemical phenomenon that is not yet perfectly understood.

Manganese was used in tableware by 1865 and in flat (window) glass in the U.S. long before 1880. A practical end date for manganese use in all but specialty bottles is about 1920, although some use continued until the early 1930s.

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.

When irradiated or exposed to the sun for many years, antique glass with manganese turns purple. There are other chemicals which have been used in old glass which change the colour of the glass when exposed to strong sunlight or irradiation.

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).

Manganese Glass (365nm)

Manganese can be found in nearly all colors of glass, especially amethyst and turquoise blue glass. Manganese fluoresces green under 365nm UV light, often being confused with Uranium.

If the glass glows a rich green color, it contains uranium. This green fluorescence explains why an example of Vaseline glass that looks yellow under incandescent lighting might take on a greenish tinge when viewed outdoors. There are exceptions.

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.)

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. That's why some antique bottles have that lovely lavender glow… but more on that below!

If the bottle seam goes to the lip's top, the bottle is likely a machine-produced bottle from 1910 to the modern era. If the seam goes to the neck's top but stops before the lip, the bottle was likely produced from 1880 to 1910. However, entire bottle classes stand as exceptions to this rule.

How can you tell if glass is vintage color? ›

Different ways to determine whether glass is antique are to study the patina, the colour, its markings and its patterns, while also looking for bubbles and a pontil mark. Also check to see if the item is definitely glass, not crystal.

Take some time and look closely at the piece's shape, surface, weight, and quality—all potential clues for you. “Is the glass transparent or opalescent or iridescent?,” Robinson asks. “Is there any decoration that might give away what it is or who may have made it?” Look to see if the glass has been signed or marked.

Solarization of Glass

It is a photochemical phenomenon that is not yet perfectly understood. It is generally accepted that the ultra-violet light initiates an electron exchange between the manganese and iron ions. This changes the manganese compound into a form that causes the glass to turn purple.

Look for pink, blue and green glassware

Pink, green and blue are the most valuable colors of depression glass. Pink tends to be the most valuable because it is more rare. Yellow and amber colored depression glass is more common and therefore less valuable.

Manganese in the glass recipe reacting with UV radiation from the Sun. So you will rarely dig a purple bottle, unless it was in the Sun before getting buried. Set em out in the sunniest spot and wait a few months for any to show signs of purple.

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.

Before 1915, manganese dioxide was used to decolorize the greenish tint of glass caused by iron. It oxidizes the iron and forces it to be a yellower, less intense tint. Unexpectedly, the manganese dioxide transforms into a pink or purple tint when exposed to ultra violet rays from the sun.