Glass has been around for centuries, used for everything from jewelry to coffee tables and windows to fine art. Back in the day, glass was something only the wealthiest of citizens could afford. In more recent times, modern glass production methods have made glass a more affordable commodity. It is common to see a variety of glass bottle shapes in grocery stores, as glass bottles are deemed food-safe containers for a number of products, including condiments, pickles, and sodas. As glass does not change the taste of the foods it contains, it’s the ideal choice for foods and beverages. Glass is virtually inert and impermeable, making it the most stable of all packaging materials and it is generally heat-resistant and, most importantly, recyclable. Its versatility continues to make it a widely-used product in every facet of life.
Start with Sand
The main material used in the production of glass is sand. Clear glass is made from a silica sand, which is a fine white sand, free of chemicals. The sand is melted into a liquid at very high temperatures by glass bottle manufacturing companies. Once melted, sand cannot be returned to its original state. The conversion changes sand into a different structure altogether. As the sand cools down, it will never form a complete solid. It remains in the state between a solid and a liquid, known as an amorphous solid. The molten glass is then placed into a mould to produce shaped glass bottles.
To begin the glass bottle making process, the silica sand must be mixed with several other materials. Soda ash (sodium carbonate) is added in a smaller percentage to decrease the melting point of the sand. This allows the sand to melt faster in the furnace, saving energy along the way. Adding only soda ash to the sand would eventually result in the production of a bottle capable of dissolving in water. To avoid such a result, limestone (calcium carbonate) must be added. The resulting glass type is then referred to as soda-lime glass, which accounts for approximately 90% of the world’s glass production.
What Is Soda Ash?
Soda ash is the more common name for sodium carbonate. It is white in color and found either in a powdery or granular form. It is used in a number of products throughout the United States and its monthly production is tracked by the Federal Reserve Board as part of the US economy monitoring system. Soda ash has been used for thousands of years, with early Egyptians crafting glass products over 5,000 years ago. The soda ash then was found in dry lake beds or as a by-product of burning marine plants like seaweed. The extraction of the plant ashes resulted in the name ‘soda ash’. Today the largest area in the world for mining natural sodium carbonate is found in the Green River Basin of Wyoming.
What Is Limestone?
Limestone is a sedimentary rock, made up of mostly calcium carbonate. It is typically formed by the compilation of organics such as coral, shells, and algae in warm, shallow marine waters. There are several natural limestone mining locations throughout the world but most notably limestone is found in the Caribbean Sea, Persian Gulf, Indian Ocean, Gulf of Mexico, around the islands in the Pacific Ocean and the Indonesian archipelago. Just south of Florida, the Bahamas Platform produces vast amounts of limestone due to the plentiful coral, algae, and shellfish found in the surrounding warm waters.
What Is Cullet?
To round out the raw materials necessary for producing glass bottles and jars, cullet is added to the list. Cullet is defined as furnace-ready, recycled, broken or waste glass. It is procured from recycled glass or waste glass. Waste glass is made up of any glass products not meeting high quality standards in the production process. Glass bottles found to have imperfections during the bottle inspection process are removed from the line and recycled into new glass production. Because recycled glass never loses its purity or quality, it can be recycled over and over without concern. Recycling glass, in turn, helps protect the environment.
Food-Safe Glass Bottles
In the United States, the Food and Drug Administration (FDA) oversees food safety regulations. The FDA is responsible for determining which materials are considered food safe, including the processes used in glass bottle manufacturing and the creation of food-safe glass bottles and jars. As part of the FDA process for qualifying packaging options for food safety, the agency considers the glass and plastic containers used in food packaging to be indirect food additives. This means the containers used to hold food and beverages make contact with the products as part of the production process. The plastic and glass used in packaging isn’t a direct additive to the products but nonetheless must be validates as safe for food applications.
The FDA has previously advised that soda lime glass bottles and jars are not "food additives". Soda-Lime glass is classified as Type I, Type II, and Type III which are all considered to be food safe, or in the terms of the FDA, GRAS (generally regarded as safe). For this reason, soda-lime bottles are very often chosen as the packaging of choice for most food and beverage products.
Type I Borosilicate Glass
A Type I glass container contains silica, boric oxide, sodium oxide, and aluminum oxide. It is suitable for packing alkali materials and acids and is considered food-grade safe.
Type II Treated Soda Lime Glass
Type II glass container is suitable for liquids and acids. It is similar in composition to Type III glass and is easier to mold than Type I glass and is food-grade safe.
Type III Soda Lime Glass
Type III glass is untreated soda lime glass offering average chemical resistance. It is made up of silica and various oxides, including sodium, calcium, aluminum, magnesium, and potassium. Type III is the most common glass type in use and is compatible with most items such as: food, beverages, and common chemicals - and, it is food-grade safe.
For an infographic on the glass manufacturing process, click here: Infographic - From Grit to Glass, How Are Glass Bottles Made.
View the video: From Grit to Glass: How Glass Bottles are Made