Marbles have been used for games and industrial tasks since the ancient Romans and Egyptians began making them out of stone, clay, and marble. Modern day marbles are made of glass. Durable, inexpensive, and beautiful – glass checks all the boxes. Maybe they should be called “glassles”… but that’s beside the point.
Read More: Glass Fabrication Explained
In this video, Science Channel’s How It’s Made goes behind the scenes to find out how one company is making marbles out of recycled glass.
In the video above, recycled glass and defective marbles are thrown into a kiln heated to 1204 degrees Celsius for 16 hours to form a colorful mixture of molten glass. While draining the molten glass, a shearing device below the kiln cuts the stream of molten every half second, forming segments, called slugs, that become marbles. To make different size marbles, the device can be adjusted to cut at different intervals.
The slugs then need to cool for 72 hours between grooves on cast iron rolls that are spinning to keep the slugs from sticking.
The marbles are then funneled into channels that weed out marbles of the wrong size and collect the ones that are perfect.
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It’s believed that the first glass marbles were made by glassmakers, who would collect all the small off-cuts from their day’s work, shape them into small balls and take them home for their children to play with.
They became known as ‘end-of-the-day marbles’, and became increasingly popular. However, the processes of how marbles are manufactured has come on leaps and bounds since then and the modern process of how marbles are made is fascinating.
First, a mixture of sand, silica, soda lime and various other ingredients are melted together for up to 28 hours in a huge furnace at a temperature of around 1300°C. Next, the molten glass – which by now has the consistency of thick treacle – is moved into a flow tank and the superheated glass is injected with more molten glass, but this time it’s coloured glass to create the beautiful swirls and patterns we recognise.
It is this injection process that takes place during the manufacture of glass marbles that determines the specific colours and patterns that are created. Iron oxide in the glass creates green marbles, cobalt is a deep blue colour and uranium oxide is yellow-green. The way the injection is administered determines the final pattern of the marble. Modern technology can now feed two or more colours into the same marble for a stunning multicoloured effect.
Once the glass has been injected with the colours and patterns, it comes out of the tank in a long strand and is cut to size. These small pieces of glass (known as globs) are then shifted through rollers that shape the glass into perfect spheres while cooling it.
The cooled and hardened marbles are then poured into containers, where they are sorted by hand. The people in charge of this process will inspect the marbles and remove any defective pieces, which aren’t thrown away but put back in the original furnace to be re-melted. Once quality checked, they then are sorted into batches to be packed up and shipped all over the world.