The traditional milk bottle is the ultimate in practical glass packaging. The height-to-diameter ratio and gently curving shape mean the bottle is light, cost effective to produce and can withstand being reused 20-30 times. The bottles reach customers unadorned except for the name of the dairy embossed into the glass.

 

David Workman, director general at trade body British Glass, explains that the embossed logos were introduced as a practical measure, to ensure the bottles were returned to the correct dairy. A label would have washed off when the bottles were reused.

 

Embossing is now used for branding rather than functional purposes. Stamping a brand’s name into the fabric of the packaging sends out strong quality cues to the consumer as well as reassuring them of the product’s authenticity. Once the moulds have been made, the branded bottles or jars can be produced in their millions at the same speed and cost as a plain version. Embossing reduces the need for secondary processes such as labelling, which can add cost and time as well as another material to sort during recycling. However, the actual process of embossing is more complex than simply deciding to put a pattern into the glass. Certain areas of a container need to be avoided, the embossing will need to line up with any labels and the complexity of the design to be embossed needs to be taken into consideration.

 

The recent trend towards lightweighting has proved a boon for embossing. O-I innovation project manager Steffi Lenz explains that because there is less molten glass to push into the mould of a lightweighted bottle it is easier to achieve finer details. The narrow neck press and blow method is much more precise for embossing than previous blow-blow technology, she says. Vacuum bores can also be added to the mould, which suck against the molten glass to sharpen embossed details.

 

Embossed areas are normally raised 0.3-0.5mm. Fine details become more difficult to achieve as moulds get older. A mould wears out the more you use it. If you are embossing very small details, the mould won’t last as long and the embossing won’t be as clear towards the end of the mould’s life, says Beatson Clark marketing manager Charlotte Taylor.

 

The same is true of debossing – where the details are sunk into the glass rather than standing out from it. The mould is the reverse of the finished product and so it has raised surfaces to create debossing. These surfaces wear down faster than the engraved details used to create embossing. Taylor says each mould will generally produce 13 million units, depending on the design. However, it can be as many as 18 million. We clean and maintain the moulds for customers to get as much life out of them as we can, she adds.

 

Drawing the line

Moulds open like a book on one side. This creates a parting line, or seam, down one side of the bottle. If the parting line runs through an embossed area it can wipe the detail off as the mould is opened, as well as looking unsightly. You need to think about where to put the parting line so it won’t go over the embossing. If you have a square-shaped bottle or an unusual shape like Gordon’s gin it can be difficult to work out where to put the parting line, says Lenz. She adds that square and asymmetric shapes can also make it more difficult to open the mould, so careful planning is required to ensure it opens without catching on the bottle.

 

The parting line can also cause challenges for labelling. Lenz explains that if a clear film label is applied over the parting line, air bubbles can form behind the label.

 

Of course, if you’ve gone to the effort of embossing a container, you want to be sure the label won’t cover it up. If you have a square jar with embossing on the sides and want a label on the front and back you need a machine that can spot the sides that are embossed. If you haven’t got a machine, you would have to turn the jars to face the right direction by hand, says Taylor.

 

There are two mechanical methods of ensuring the bottle or jar is facing the correct direction for labelling. A spotter bar uses a notch at the bottom of the bottle. A metal bar is inserted into the notch, mechanically turning the bottle to face the right way. Alternatively, a row of dots can be embossed near the base of the bottle. An optical reader spins the bottle so the label is placed in the correct spot relative to the dots. The method used will be determined by the equipment of the company doing the filling and labelling. Taylor adds that some brands will choose to emboss all the way round, to avoid the need to align the label to the embossing.

 

When bottles are on a filling line they rattle along at impressive speeds, one pressed up against the next. Quinn Glass sales manager Gillian Walters says most bottles are designed to have two points, one upper and one lower, that will be in contact with the bottles on either side. These will be the widest points and need to be tough. On reusable bottles, such as glass Coca-Cola bottles in some countries, a scuffed ring will be visible at the contact points.

 

On the Carlsberg beer bottle the contact points are at the shoulder and the heel. The middle is slightly recessed, so this doesn’t touch anything, which makes it a secure spot for embossing, explains Walters. If a bottle were embossed over the contact points, the embossing would be at risk of chipping or cracking as it is bashed into the bottle next to it. The two contact points also need to be the same width, otherwise the bottles might tip over on the conveyor belt.

 

Adding value

Making a custom mould is expensive. But there are other options. Tim Croxson, operations manager at glass packaging supplier Croxsons, says bespoke runs of as few as 40,000 units are possible. Using a blank mould from an existing design coupled with a new finish mould allows brands to dream up a new bottle for a lower cost than making a full custom mould.

 

He adds that embossing is not confined to the glass – caps and closures can be embossed, while other effects such as photo-quality digital printing are also available for caps. Many clients use closures as a different method of adding value and shelf presence, he says.

 

To ensure that customers are pleased with the results after splashing out on a custom mould, Ardagh Glass has invested in technology to provide a mock-up of the final product. We use Perspex blocks, which are cut and engraved on a lathe. Then we create a mould. When you take off the mould, you have a model of what the embossed bottle will look like, says head of marketing Sharon Crayton. She says the Perspex trial helps to get the embossing right. Sometimes designs will be too intricate to emboss clearly and customers will be disappointed with sharpness or clarity. Crayton says that working with customers on the design of their embossing and making samples ensures the finished product is something the brand can be proud of.

 

Embossing was once the preserve of premium spirits and perfumes. Now, growing numbers of beers and FMCG products are using it to add panache. The flexibility of glass to create unusual shapes and intricately embossed designs is one of its selling points as a packaging material. However, is there a danger that embossing will lose its impact as it becomes more ubiquitous? Design Bridge head of 3D structural branding and packaging Nick Verebelyi says not. Every bit of embossing is different. Everyone wears clothes, but you still notice different fashions.