Through the Looking Glass: Maritime Glass as Sea Glass

maritime sea glass

It is quite possibly the hope of many a sea glass collector that the perfectly aged specimen of colorful glass they’ve recently fished off the local beach has a story to tell of a centuries old ship lost at sea, her bodies and contents swallowed and storm-tossed and only now, with the passage of tides and time, come to light. A romantic notion, and so much better than the reality—that chances are it is the result of purposeful littering, or garbage dumping. We don’t want to believe that so much (80% to 90%) of the sea and beach glass we find doesn’t have a greater story to tell, or that it is, in fact, just trash.

Maritime glass, such as it is—glass that was made for a utilitarian purpose aboard a ship—is very unlikely to be the source of your precious beach glass find. Sure, there was glass used aboard ships. And there were certainly plenty of ships sailing the lakes and seas throughout the centuries. But the ship would have to wreck to cast the glass to the bottom of the ocean or lake, and the glass would have to age and then resurface as your beach glass.

antique oil lamp

Because the glass aboard a ship generally did have a purpose, it was not likely to be tossed overboard as refuse. On the other hand, ships did find their way to the bottom of the seas, sometimes at an alarming rate. By one report, during the winter of 1820 alone, more than two thousand ships were wrecked in the North Sea alone, causing the deaths of twenty thousand people, and scattering upon the sea floor so much timber and cargo and sailors, and even the glass employed by the ship.

Nautical Tools

How much glass was really used on a boat or ship? Rough seas and high waves could not have been friendly to glass. Yet, it was used—and earlier and more prolifically than you might expect. Items of necessity such as the spyglass (the original nautical binoculars) possibly first use in the 1600s, and the maritime sand-glass (nautical hourglass) employed possibly as early as the 14th century, were common stock aboard ships.

The sand-glass, which was made just as an hourglass with two connected globes filled with sand but usually housed between four wooden columns, was used to measure the passage of time and was critical for navigation prior to the 19th century. However, it wasn’t the most exact tool, as it relied on a person actually flipping it over at precise increments (when the sand was emptied from the top to the bottom, usually every half hour) to keep good time. There is an old mariner’s phrase, “flogging the glass” which explains how inaccurate the sand-glass could be when manipulated: the course of the sand was known to be hastened by vibration, hence some weary seaman towards the end of his watch was said to speed things along by flogging the glass.

Ships have long been equipped with compasses and chronometers, a timepiece first used in the late 1700s and made accurate enough that it could determine longitude via the sun or moons or a planets position in relation to the horizon. Both the compass and the chronometer often would have included a glass covering lens.


green oil lantern

For most of the Age of Sail, the enclosed decks of a ship were like tombs, dark and dank, and if not for openings in the hull and decks, or artificial lights, they would have been as dark as night even in the daytime. Portholes had been around for many centuries. Some stories credit Henry VIII with their origination; at some point during his reign in the 15th century, he insisted on using cannons on his ships that were just too large and thus holes had to be cut into the side of the ship to accommodate them. It was apparently a French shipbuilder who was called upon to solve the problem and created the side holes, and then covers for those holes for times of inclement weather. The French word for door was porte, and likely the term corrupted over time to have become porthole. The first glass used in portholes was much thicker than even today’s porthole windows and likely not very clear.

Another solution in lieu of the dangerous candles or kerosene lamps for below-decks lighting was the deck prism. These were cut pieces of glass, the flat top laid flush in the deck and the prism-ed glass hanging under to illuminate the deck below by refracting sunlight. The prism shape of the glass would cast a much larger spray of light than a flat pane of glass. Lovers of lavender sea glass will be encouraged to know much of the early deck prism glass was made with manganese to keep the glass clear (before it was realized that manganese actually turned purple after years of exposure to sunlight).

red lantern

Oil lamps had been lighting ships since almost as long as humans have been sailing. Glass was introduced to maritime oil lamps in the 17th or 18th century, consisting of two parts—the inner chimney covering the flame, and the exterior thick glass which was routinely housed in a metal cage or brass or copper housing for safety.

Navigational Lighting

Antique marine navigational lights can be found in an array of colors. Law in both the United States and the United Kingdom have been on the books since the first half of the 1800s, though initially only the UK specified that vessels were required to carry specified colored lamps. These laws were introduced as part of attempts to make sea travel safer, certainly as it increased in the first parts of the 19th century. The most common colors were red to indicate port side, green for starboard, and clear for the aft or stern (rear of a ship). Antique navigation lights abound on the internet, some hundreds of years old, in a wide spectrum of colors including several shades of blue, and purples, yellows, and orange.

red ship lantern

Some of the very old navigation lamps and stern lights from long-gone ships were very ornate, almost works of art by themselves.  The 20th century offerings were more mechanical in appearance, and most of these would have been fitted with a Fresnel lens.

A Fresnel lens, so named for the French physicist Augustin Jean Fresnel, who designed it in 1822, is a glass lens with a complex system of multi-faceted glass prisms. The prisms reflect and refract (bend) light and magnify it, thereby taking rays of light that would normally be strewn in all directions and focusing them into a single beam. Many lighthouses use Fresnel lenses, some of which are 10-15 feet tall and can be seen from as far as 20 miles away. The smaller ships’ lanterns made with a Fresnel lens would still be visible from enough distance away to avoid collision. Sea glass of a Fresnel lens origin will have noticeable ridges in a relatively thick piece of glass.


The term "drunken sailor" isn’t a part of our vernacular without good reason. (Alcohol in general, and sailing, have a long and colorful, sometimes licentious history). While the average sailor did imbibe almost daily, he likely would have taken his spirits from a wood or tin or bone horn, or mug, rather than from glass cups. But his captain and officers possibly drank from fine glasses, the liquor itself held in ships decanters, wide flat-bottomed serving pieces of glass, usually complete with flat stoppers that were unlikely to roll when set down. The decanter was made of high quality glass and blown quite thickly to withstand the rigors of a sea voyage.

antique medicine jars

Meanwhile a sailor, drunken or otherwise, was a regular visitor to the ship’s surgeon. Not every ship had one, and if they did, they were not always educated to the degree you’d hope of the man sometimes standing between you and death. A ship’s medicine chest would have been stocked to treat a vast selection of maladies from simple drunkenness and the nasty scurvy, to amputations and battle wounds. Enter the glass—bottles and bottles of squat and small vial and flasks, filled with all manner of herbs and medicines. Spirits, salts, and solutions were kept handy and doled out on likely a daily basis. Cinnamon water or licorice juice cured hiccups and might stop vomiting; salt of wormwood, vinegar, and quicksilver (mercury) were given for urinary problems and fevers; Peruvian bark (quinine) was kept onboard to treat malaria—the list goes on as life aboard the old sailing vessels was not a healthy one.

While you may be sure you’ve found a great piece of maritime glass, there is no indisputable means to identify your found sea glass as having come from a wrecked ship, unless you’ve dived and recovered the glass yourself (it is generally frowned upon to remove any artifacts from shipwreck; "take only pictures, leave only bubbles"). Almost all glass that was employed on ships was also either utilized on land as well, or could have been simply discarded once the ship no longer was in service. As with the majority of our sea glass, we might just never know its true origin.

This article appeared in the Glassing Magazine November 2017 issue.

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