Glass packaging is made of predominantly natural ingredients: silica sand, soda ash and limestone.

how glass bottles and jars are made

Glass packaging is made of predominantly natural ingredients and includes silica sand, soda ash and limestone. These and other key materials are mixed with recycled glass, called ‘cullet’, to make up the batch mixture.

The batch mixture is heated in the furnace to about 1550 degrees Celsius to create molten glass. The furnace runs 24 hours a day, seven days a week, and can process several hundred tonnes of glass each day. Many Visy Glass plants have multiple furnaces.

When the molten glass mixture comes out of the furnace, it flows into a refiner where it cools to around 1250 degrees Celsius and air bubbles escape. The molten glass then goes to the forehearth, which brings the glass temperature to a uniform level before it enters the feeder. At the end of the feeder, shears cut the molten glass into ‘gobs’. Each gob will eventually become a glass container.

Each gob is dropped into a series of moulds inside the forming machine. Compressed air is used to shape and expand the gob into a glass container. The glass continues cooling, dropping to around 700 degrees Celsius.

Each glass bottle or jar then goes through an annealing step. Annealing is necessary because the outside of the container cools more quickly than the inside. The annealing process reheats the container and it is then gradually cooled to release stress and strengthen the glass. Glass containers are heated to about 565 degrees Celsius and then cooled slowly to 150 degrees Celsius. Then the glass bottles and jars are put through the cold end coater for a final outside coating.

Each glass bottle and jar is put through a series of inspections to ensure it meets Visy’s standard. Multiple high resolution cameras inside machines scan as many as 800 glass bottles each minute. The cameras sit at different angles and can catch miniscule defects. In another part of the inspection process, machines exert pressure on the glass containers to test wall thickness, strength and if the container seals correctly. Visy Glass experts also manually and visually inspect random samples to ensure quality.

If a glass bottle or glass jar doesn’t pass inspection, it goes back into the glass manufacturing process as cullet. Containers that pass inspection are prepared for transportation to food and beverage manufacturers, who fill them and then distribute them to grocery stores, restaurants, hotels and other retail locations for shoppers and customers to enjoy.

Once consumers and restaurants recycle their glass bottles and jars, the bottles are sent for sorting and separation. The separated glass bottles and jars are broken into glass cullet and large residual contaminants removed. Glass cullet is sorted by colour and small contaminants removed by optical technology, leaving the recycled cullet ready for the manufacturing process.

Glass is recyclable again and again, and a recycled glass container can go from the recycle bin to store shelf in as little as 30 days. The glass manufacturing loop repeats over and over, and so the story continues…