What is Sea Glass? We Reveal the Secrets of Beach Treasure

A selection of sea glass found at Seaham, United Kingdom.

Sea glass is formed from discarded glass products that have rolled around in the ocean, breaking down and interacting with the waves, sunlight and chemicals in the saltwater.

Where does sea glass come from?

It was common in the past to simply dump trash into the ocean, especially along shipping lanes and shorelines. Much of that trash included glass products, such as broken tableware or auto tail lights.

Glass bottles covered in barnacles, brought up from a ship wreck.

There are also thousands of shipwrecks at the bottom of our oceans,  it's possible for some glass bottles and fine pottery items to be stirred up due to storms and wave activity and may eventually find their way to our beaches.

While most non-glass items decomposed due to the salt air and sea water, glass continued to tumble back and forth with the tides. Over many years, the composition of the glass changed due to the pH level of the salt water.

How long does sea glass take to form?

The entire process can take ten years, fifty years, or even longer! It varies depending on a number of factors, including location, wave activity, rocky or smooth bottom ocean floor and higher or lower pH levels.

Glass transforms quicker in water that has more wave activity and higher pH level. Seawater has a pH level of at least 8, which makes it alkaline and oxygen-rich.

Fresh water lakes, streams and ponds tend to have pH levels ranging from 6 to 8. An exception to this is Lake Erie, with an above average pH level of 8-9. The lake is very well known for its abundance of frosty beach glass.

Frosted sea glass

When sea glass is dry, it takes on a frosted appearance even after it's been washed. This is called "hydration".

Hydration is the process in which the soda and lime content in the original glass are leached out by exposure to salt water, leaving pitting on the surface. The pits sparkle in the sun because of tiny crystals which are formed when the lime and soda combine with other elements on the surface of the glass.

Sea glass has been dragged through the constant pounding surf, sand, underwater rocks and sea shells. This results in it being broken up into small pieces and tumbled smooth by the waves , then tossed onto the shore. A quality piece of sea glass has no shiny spots, no chips is well frosted and thick, smooth, rounded edges.

If you prefer a smooth, wet look to your sea glass, rub it with a drop of oil right after you wash and dry it. I find that baby oil works really well!

Sea glass rubbed in oil
Jonna Marie 
Sea Glass Collector
Detective work!

For beach combers, there is no better moment than spotting a piece sea glass glistening in the surf. If it's weather-worn and wave-tumbled, even better!

At this point, your imagination is ignited:

  • What was it before it was broken?
  • Who owned and used it?
  • What time in history is it from?
  • How many years has it been tumbling in the waves?
  • Was it tossed over a cliff as discarded trash or lost overboard an old shipwreck?

So many unanswered questions! It's time to look at the clues...

Sea glass color

The color of the glass is your first clue. The most commonly found colors depend on the area and the age of the site. You will find though, that green, brown and clear are the most common colors just about every place. These pieces were originally from bottles and household jars.

Green sea glass from Capistrano Beach, California.

This chunk of green glass was probably from an old bottle.

Other colors are harder to find, such as sea foam and olive green, aqua, cobalt blue and amber. These pieces were once medicine bottles, glass fishing floats, soda bottles (think Coca-Cola!) and cosmetic (Noxzema and Vicks -vapo-rub ) jars.

Then you have amethyst, gray, black, teal, lime green, cornflower blue, pink, peach, lavender and turquoise. The origin of these colors may have been perfume bottles, old seltzer bottles, power line insulators, figurines and candy dishes.

Only one in five thousand pieces collected is red. It has often come from ship lanterns, streetlamps and car tail lights.

Even more rare though are orange and yellow, only one in ten thousand pieces collected! These would have come from tableware or, perhaps, art glass.

Shape of the glass

This is another big clue. You will quite often recognize right away when a piece of glass has come from a bottle, perhaps you'll even be lucky enough to find an entire bottle neck. I'd love to find just the upper ring of the neck lip. Finding a bottle bottom with raised numbers or writing on it if fun. Coke bottle bottoms are a great find! They often tell you when and where it was bottled.

Bottle stoppers are also easy to identify, as are marbles which were often used as ship ballast.


Where you find the glass is also going to help identify what type of object it came from originally. For example, a thin piece of green or brown glass on a busy public beach is likely to have come from a modern beer, wine or soda bottle, whereas a colorful and rounded chunk of glass at Davenport, California will almost certainly be from the Lundberg Studio. 

Sea glass from Lundberg Studio, Davenport, California.

Sea glass from Lundberg Studio, Davenport, California.

Happy hunting​!

Finding sea glass is only half the fun. For many collectors, trying to unravel the mysteries of the past is just as exciting and leads to daydreams of what might have been a century or more ago.

Happy hunting!​



I have been gathering sea glass for many years. I can never resist a stroll along the beach and the opportunity to add some more beach treasure to my collection!

1 Comment

  1. Is it possible to purchase a large order of sea glass and what would it costs for 200# of glass shipped to Michigan. Interested in purchasing multicolored glass for a garden.

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