Labelling on glass jars

Glass is still widely used in the pharmaceutical industry, especially for products where high demands are placed on chemical resistance, sterility and long shelf life. Glass containers are used for liquid medicines, injection solutions, laboratory reagents and other products where the properties of the material are crucial for the quality of the product.

Unlike cardboard packaging or plastic jars, labelling glass jars is significantly more demanding due to the surface. The material's hard and often slippery surface, high production rates and the requirements for sterile handling mean that both labelling technology and production line must be carefully adapted.

At Logimark, we help pharmaceutical companies choose labelling technology based on the entire production process – from filling line and sterilization to final quality control and traceability.

Function of the glass container

A glass container is the primary packaging and is in direct contact with the drug. It must not only protect the contents from external influences but also ensure that the properties of the drug are preserved throughout its shelf life.

Common uses are:

• liquid medicine
• injection fluids
• oral solutions
• laboratory chemicals
• diagnostic products

Since the glass container is often the packaging used directly by healthcare professionals or patients, the labelling must be clear, durable and easy to identify.

High production rates place high demands on the labelling system

One of the biggest differences compared to carton packaging is the production rate. Glass containers often come directly from filling lines where liquids are filled automatically. These lines typically operate significantly faster than carton lines. This means that the labelling system must be able to apply and verify the label without limiting production capacity.

In practice, the challenge is therefore not just about writing the correct information – but about doing so with high precision even at very high line speeds.

Glass requires careful handling

Another important aspect is the product itself. Many glass containers contain high-value or highly sensitive pharmaceuticals. In addition to the risk of losing the product, broken glass can mean:

• contamination of the production line
• production stoppage
• scrapping of entire batches
• extensive cleaning and revalidation

Labelling systems and conveyor belts must therefore be designed to handle the glass containers gently and with high mechanical precision.

The environment affects the labelling

Glass containers often go through several processing steps before leaving production. Depending on the product, they may be subjected to, for example:

• sterilization
• autoclaving
• cooling
• freezing
• high humidity
• disinfectants and alcohol-based cleaners

This means that the label must remain legible even after these processes. Therefore, even in the design phase, it is necessary to take into account the environments the product will be exposed to during its life cycle.

Release agents on glass – an often overlooked challenge

A detail that is rarely noticed is that many glass containers are treated with a very thin layer of silicone-based release agent. The purpose is to reduce friction between the glass containers as they are transported through the filling line. The treatment makes the glasses slide more easily against each other and reduces the risk of scratches and glass damage.

This poses a technical challenge for the labelling process. The silicone coating can impair the adhesion of the ink to the glass surface. The result may be that certain ink types do not adhere well enough or have poorer durability. Therefore, material testing is often a crucial part of the design when labelling on glass jars is to be used.

The color of the glass affects the choice of ink

Not all glass containers look the same. In addition to clear glass, the following are often used:

• brown glass
• green glass
• opal glass
• dark special glass

The color directly affects the contrast of the marking. For example, black ink works great on clear glass but provides significantly poorer contrast on dark glass containers. In these cases, other ink colors or alternative marking techniques may need to be used to achieve sufficient readability.

The marking technique is chosen based on the entire process

When it comes to labelling glass jars, there is rarely a one-size-fits-all solution. The choice is influenced by factors such as:

• production speed
• the surface treatment of the glass
• the color of the glass
• sterilization processes
• traceability requirements
• verification requirements
• integration into the filling line

It is the interaction between these factors that determines which solution provides the best operational reliability and lowest total cost. At Logimark, we therefore always start from the entire production process when we design labelling solutions for the pharmaceutical industry.

The goal is not just to create a readable label, but a robust and validable process where each glass container can be identified, verified and tracked throughout its entire lifecycle.