Photography and text by Sara Caruso
Without a doubt, one of the main things that draws beachcombers to sea glass is its uniqueness. No matter what it came from, or how long it’s been in the water, no two pieces of sea glass are alike. This keeps collectors on their toes as every trip to the beach yields something they have never seen before. But have you ever considered how sea glass gets its shape? Why are so many pieces triangular and diamond-shaped? It all comes down to the chemistry of the glass, how the glass was made and changes to that process over the decades.
Every piece of sea glass has a different molecular structure because glass is an amorphous solid. When a liquid transitions into a solid state, such as water into ice, the molecules quickly arrange to form a repeating pattern — an ordered crystalline structure. However, as molten glass cools, the movement of these the molecules slows gradually, creating a random arrangement instead of an ordered arrangement. This helps glass to be more flexible, which is great for windows that are constantly exposed to the elements. However, each piece of glass has invisible weak points within this chaotic molecular structure. If the glass breaks, it will be along these weak points. As the glass tumbles in the surf, the sand, and stones around it further shape the shard into a smooth treasure.
When a piece of sharp glass enters a body of water the amount of time it will take to become sea glass depends on numerous factors. Every beach is different. If a beach has calmer waves, glass may take longer to become worn or may never be worn down at all. Examples of this include bays and rivers where very old, large pieces of glass with little wear are frequently found. But if a beach has strong tides, huge waves, and heavy storms, glass may get very worn over a shorter period of time. Pebbles and sand also help to chip away and reshape the glass. The process by which the glass was manufactured may also play a role in how it breaks down later.
Glass blowing had not changed much in thousands of years until the late 19th century when the process of free blowing bottles and glassware by hand was changed over to mold blowing. This technique requires a glass maker to blow a gob of molten glass into a mold. The glass is pushed against the walls of the mold, taking on its form. These early techniques caused bubbles to form in the glass, which were usually ignored unless it caused the contents of a bottle to leak. When exposed to the elements, especially rough waves and seasonal temperature changes, the glass would break along the weak point of the bubble. Later glass making technology would eliminate the need for the human blower, and instead mechanically force glass into molds resulting in fewer bubbles and or defects and smaller shards.
The advent of recycling further effected the way glass was manufactured. For glass to be broken down and recycled, the walls of bottles had to be thinner. This new thin glass, made from the 1970s to today, makes for poor sea glass as it breaks down into ever smaller bits. Once glass breaks down completely, it is similar to sand. While not great for sea glass collectors, it is better for the environment. Eventually, all sea glass will return to sand-like grains if not found by a beachcomber.