Why Glass Comes in Different Colors

Glass is renewable and one of the only materials that can be endlessly recycled without losing strength or quality, so the glass found in your spaghetti sauce jar or wine bottle can go from the recycling bin to store shelves in as little as 30 days.

Color Significance

Have you ever wondered why beer usually comes in amber glass and wine is often in green glass?

  • Brown glass absorbs the most ultraviolet radiation, at wavelengths shorter than 450 nm (nanometers), so it offers the best protection from potentially damaging light. Beer, for instance, would be ruined by light absorption so you’ll usually find your favorite brew in a brown bottle.
  • Green glass still has light protection, but not as much and since liquids like wines and juices can be exposed to some light without ruining the flavors, they are often bottled in green glass.
  • Clear glass is best suited for alcohol, water, sauces and foods that aren’t affected by light.

All of these glasses are colored by the addition of oxides colorants to the forehearth, a brick-lined canal that delivers glass to the forming machine of a flint glass furnace, during the manufacturing process.

Iron, sulfur and carbon are added to make amber glass. Chrome oxide is used to create green glass; the higher the concentration, the darker green the glass will be. Blue glass, which was more popular in the 1920s, is created by adding cobalt oxide.

Separation and Recycling

Because the color is significant during the manufacturing process, it makes sense that color would play a role in recycling as well.

“Color separation is a necessity,” says Phil Ross, technical consultant for the Glass Packaging Institute. “Recycled glass that has cross mixtures will impart a tint in a clear container.”

Ross says that due to the proliferation of single-stream recycling programs, it’s hard to get a really clear glass anymore because glass colors can easily get mixed at the point of collection and at the materials recovery facility.

Also, more contaminants are present during final separation and recycling. “Newspaper people complain about getting glass in their paper and glass people complain about getting contaminants like coffee mugs,” Ross says.

If contaminants do get into the glass stream and they don’t fully melt, they could cause potential defects to the glass. However, manufacturers usually remove the faulty containers during the process before they reach consumers.

“In some cases, they [the faulty containers] can be recycled, remelted and formed again,” Ross says. The multiple melting may mean that the contaminants get small enough to no longer affect the container.

Benefits of Using Glass

Beer, wine, juice, sauces, water and many other things are often found in glass containers for a variety of reasons. Glass is essentially inert, meaning that it lacks chemical reactions, making it a perfect food container because it won’t affect the taste.

Consumers can see if a product is fresh because of the transparent aspects of glass, and “glass is tamper-resistant; you can’t inject a hypodermic needle or anything like that,” says Ross. It’s nonporous and doesn’t deteriorate or stain.

It’s also rigid so it can be put under pressure or vacuum, which is important when it comes to shipping, so is the fact that it has a strong vertical strength that allows it to be stackable.

More than that, the biggest benefit of glass is the fact that it’s a renewable resource that can be endlessly recycled without losing quality or strength.

Industry Trends

In the past three decades, glass bottles are about 40 percent lighter. Ross says that lightweighting, this act of using less glass to make a product, has been around for years, but many companies are getting on board with the trend.

In 2010, O-I, a glass container manufacturer, announced it was launching the lightest wine bottle in North America, weighing 11.6 ounces, which is 27 percent lighter than similar bottles.

Lightweighting helps manufacturers in a number of ways – more glass can be made from the same amount of materials, more containers can be made because it takes less time for the glass to cool and more uniformity means stronger glass.

The process also reduces emissions. For instance, O-I estimates that their super-lightweight bottles have saved more than 89 tons of carbon emissions.

Earth911 partners with many industries, manufacturers and organizations to support its Recycling Directory, the largest in the nation, which is provided to consumers at no cost. The Glass Packaging Institute is one of these partners.

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