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How glass is made?

The glass production process

Glass has been used for thousands of years. This material was discovered by our ancestors when it was found that a lightning strike or hot, volcanic lava melted quartz sand. Over the years, humankind has built on nature’s revelation, and the production of glass has grown and grown. Stoelzle are globally renowned specialists in this field, and with over 200 years experience, our passion and excitement remains. We welcome you to enter our world and learn more about this fascinating process.

Unlock the art of glass making!

Have you ever wondered about the magic behind the making of glass? Let’s follow the glass through those stages cameras usually fail to capture.


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Green cullets

What are the raw materials of glass?

At Stoelzle, we produce type II glass (treated soda lime glass) and type III glass (soda lime glass). These are, indeed, the most popular types of glass used industrially. The raw materials applied in the process are:

  • quartz sand
  • limestone
  • soda
  • recycled cullet

The sand is the main component, limestone provides stability and soda lowers the melting point. As we work towards becoming more sustainable, we also use recycled cullet to help save on the use of raw materials and energy. After the raw materials have been precisely weighed, they are carefully mixed together. Subsequently, the collection of raw materials, which is also referred to as batch, is ready for melting.

Melting within the glass manufacturing process

The melting process can be divided into three main steps:

  1. First, the batch is placed in a furnace that reaches temperatures of up to 1,600 °C. There, the solid components slowly melt into a homogeneous mass.
  2. In the next step, purification begins. This means that the gases are expelled, which is essential for producing a higher quality glass.
  3. During the final phase, the mass is cooled down until it reaches the right temperature needed for shaping.

Glass drop is falling down into the mould
Glass shaping process

How is glass shaped?

The forming process begins in the feeder. Here, gobs of glass are cut off, which are then formed into the required shape using the IS machine. Using the blow-blow or press-blow process the machine works very quickly to configure the viscous liquid into finished products. The formed glass containers and bottles are then transported on a conveyor belt for cooling.

Two methods for shaping glass containers

The term ‘blown glass’ denotes moulded glass, where gobs of heated glass are directed into a moulding machine. From here the material enters the cavities, where air supply forms the neck and the general shape of the future container. The temporary shape is called ‘parison’ and refers to the unshaped mass of glass right before it is moulded into its final form. In order to create the final glass bottle or jar, one of these two processes can be applied:

  • Blow and blow process: This method is utilised especially for narrow containers such as glass dropper bottles or boston round bottles. Here, compressed air is better able to form the parison.
  • Press and blow process: This method is applied for large diameter containers such as wide mouth packer bottles. Here, the glass is pressed against a blank mould with a metal plunger in order to form the parison.

From hot to cold – Annealing process

Annealing describes the process in which the glass containers are cooled down after the moulding process. This is achieved in a heated furnace called “Lehr”, where the glass is slowly cooled down to avoid breakage or damages. The temperatures of this cooling area are between 590 °C and 450 °C.

During the cooling process, the outer surface of the glass products is treated with a coating which serves as a surface refinement and a protective layer.

Glass jars comin out of the tunnel
Multi camera bottle inspection at the Stoelzle Cold End section

Quality control in glass manufacturing

At Stoelzle, we care about everything we produce and quality is a top priority. For this reason, our glass products go through an extensive inspection process after leaving the Lehr. Numerous automated inspection machines are in place where all containers are checked for defects and rectified if necessary.

From glass manufacturing to glass packaging

We are proud to offer our customers an extensive range of products boasting a plethora of uses. Our vast array includes pharmaceutical packaging, cosmetic glass packaging and tableware as well as glass packaging for food, beverages and prestige spirits.

Different bottles with caps and closures
Automated packaging machine

Packaging safely for transport

Glass, by its very nature, is a fragile material, which makes packing our products all the more important. To ensure our products reach our clients in exceptional condition, we diligently pack them so we can be confident that the containers and bottles are absolutely safe for transport. We are proud of our responsible packaging and remain flexible to the needs and wishes of our customers. From large and small trays to shrink packaging, rental boards, cardboard or plastic layers to Euro or industrial boards. We source the perfect solution.

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