Written and photographed by Sara Caruso

Updated from the Spring into Summer 2014 Edition

With eyes trained for rare colors, many sea glass hunters often overlook what is right under their noses. Amid the weathered pebbles and timeworn shells of low tide there may be a hidden gem that is as rare as it is old.

In bottle collecting, the term black glass is used to refer to any glass that appears solid black until you hold it up to a light source, allowing the true color to be revealed. Most black glass found along our beaches originated from liquor bottles from the mid to late 1800s. The color of the glass was intentionally made dark to protect the contents from the destructive UV rays of sunlight. These black glass bottles are usually a deep olive green or very dark amber. The colors were the result of high amounts of iron oxides in the sand, as well as carbon and sulfur from the coal used to heat the glass furnaces. In addition to liquor bottles, other glass items such as inkwells, buttons, and insulators, along with chemical and medicine bottles were manufactured in these ultra dark shades. There are, however, even rarer colors hiding in black sea glass.

Black amber glass was commonly used for liquor and chemical bottles, and laboratory glassware. Certain chemicals, such as hydrogen peroxide, need to be protected from light or it becomes less effective. Deep black blues also had a similar purpose, being used for poisons and medicines, but also wines and perfumes. One of the most sought-after types of black glass is deep purple, which some collectors consider rarer than red sea glass.

Deep purple, sometimes called black amethyst glass was made by adding a large amount of manganese dioxide during the glass manufacturing process to create a dark color. Many sea glass collectors may have this color of black glass in the form of a lightbulb vitrite. These are insulators located on the bottom of standard incandescent lightbulbs. Decorative glassware and inkwells were also intentionally made in a deep amethyst color. Deep purple black glass can also be found in beads and Victorian mourning buttons. These would have been part of a lady’s funeral attire and often featured elegant patterns such as flowers.

Another source of black glass is Vitrolite, a high strength structural glass that was introduced around 1900 as a nonporous, sanitary, and economical substitute for marble. Manufactured as glass slabs, Vitrolite was used on building facades, kitchen and bathroom walls, business signage, and areas requiring a hygienic surface. Pieces of Vitrolite will often be very dark amber, green, purple, or teal with thin ribs along one side. The origins of sea glass never cease to amaze.

A common misconception among those new to the sea glass community is that all black glass is pirate glass. The black glass found on beaches today generally dates from 1850 to 1920, long after traditional pirates were sailing the high seas. Unless a piece of glass or bottle came from a known wreck, there is no way to know for certain that it was from pirates. There are, however, ways to make an estimated guess as to what era the sea glass originated.

If you were a sailor, merchant — or yes, a pirate — on the seven seas, keeping scurvy at bay was a big priority. Deep green onion or mallet bottles so named for their shape were kept onboard most ships in the 17th, 18th, and 19th centuries. The bottles contained lime juice for scurvy prevention, gin, rum, or grog, a watered-down alcohol and lime juice mixture. Water was either a luxury or too contaminated to drink, so these bottles of liquid were an important part of a ship’s inventory. One way to tell if you found a piece from these bottles is the glass will be very thin and often have a rough surface with an abundance of bubbles, as these were hand blown. Some may have a rainbow-like patina on the surface of the glass, known as Benicia iridescence and patina. This multicolored sheen is caused by a chemical reaction between the glass and the elements it was exposed to over an extended period of time. However, the majority of rum, gin, whiskey, and medicine bottle pieces found on our shores were never on a ship or part of a shipwreck.

Many of the squeaky-clean beaches we admire today are a far cry from those of 150 years ago. Visitors did not think about the impact their trash had on the ocean. Tossing bottles into the water or leaving them on the beach was commonplace. Storms also played a role in scooping up refuse into the waves. By the late 1800s, going to the beach in the summer became a big part of coastal economies. As a result, beaches where hotels, city centers, and shipyards were located, and bay beaches are hot spots for finding older sea glass.

Remember, black sea glass frequently goes unnoticed, especially on beaches with a lot of pebbles because it can look like a black stone, so it is important to check with your phone’s flashlight or by holding it up to the sun. You never know what secret color it may be hiding.

Seeing a piece of black sea glass reveal its true color as you hold it up to the sun is a thrill like no other. Perhaps the next piece you find will reveal a color you have never seen before. It is this thrill that keeps the sea glass collector looking for more.

Like the sea, black sea glass will only reveal its true self if you search for it.

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