Can glass go yellow over time? Laminates, interlayers and ageing

Glass yellowing is a problem mostly caused by poor manufacturing. Find out how to sort the problem at the procurement stage.



When you invest in glass for a building project, longevity is a key concern. The glass has to do lots of things at once – from thermal efficiency to aesthetic enhancement – and you want it to do those things for a long time.

The problem is that some types of glass can develop a yellow tint over time. There's a range of causes for this, but the number one cause is buying poor-quality glass from poor-quality suppliers.

It's one of many compelling reasons for sourcing your glass from a reputable, experienced supplier like ToughGlaze. With a strong reputation and experience come peace of mind for you, your stakeholders and building users.

In this article, we look at the main reasons glass sometimes yellows over time. We also show how you can nip this problem in the bud at the procurement stage.

Why can glass go yellow over time?

The main cause of yellowing glass is the natural ageing process. This only really applies, however, to older types of glass – in particular, those that contain impurities or certain additives.

With these older products, decades of exposure to ultraviolet (UV) rays and heat can cause your panes to yellow.

In laminated glass products, the interlayer rather than the glass is the problem. Before we look at why this is, it's worth reminding ourselves what laminated glass is and how it's constructed.

Laminated glass is made from two or more sheets of glass bonded with a plastic interlayer.

This interlayer is primarily for structural stability. It takes intense force to break a laminated glass unit – and when it finally breaks, the interlayer is designed to hold the pieces in place.

The interlayer can also be used to add colouring, additional sound insulation or – in the case of intumescent layers – fire protection.

In some applications, particularly car windscreens and some kinds of architectural glass, the interlayer can yellow as it ages. Because of the nature of laminated glass, this can make the whole unit appear yellow.

Protective coatings and films, too, can discolour over time. This can be the case even if the glass itself stays as clear as the day it was fitted.

Surfaces can become stained from a variety of sources. Common causes of surface yellowing include nicotine, cooking grease, air pollution and hard water deposits.

Unlike the other kinds of discolouration we've looked at, these kinds of contamination can be removed with a proper clean.

Why does laminated glass sometimes yellow?

In many modern glazing applications, laminated glass is a must. This is partly a case of building regulation compliance and partly because of its many benefits.

That said, the interlayer between the outer sheets can yellow with age. This then gives a yellow appearance to the glass, even though the glass itself hasn't yellowed.

There are several causes of interlayer discolouration. UV radiation can degrade polyvinyl butyral (PVB) interlayers. This leads to a yellow or amber tint.

As so often, this is typically the case with older products. Many modern laminated glass products have UV inhibitors that significantly delay this process.

High temperatures, like UV, can accelerate the chemical ageing process. This is especially common when laminated glass is used in conservatories, skylights and south-facing windows.

Then there's moisture. If the edge seal is damaged, moisture can enter the unit. This can cause yellowing, haziness, bubbles or even delamination – a phenomenon where the layers begin to separate.

Last but not least, laminated glass can turn yellow on exposure to certain cleaning chemicals, solvents and pollutants. This is typically a problem, however, only if the edges have been damaged.

Does all laminated glass yellow?

Yellowing laminated glass is a problem, but it's far from inevitable.

It's mostly a problem with older laminated glass products. High-quality, modern laminated glass is designed to stay clear for decades.

This is partly because of improved PVB interlayers or because the interlayer is made from ionoplast (SGP) or EVA.



Can yellowing be fixed?

Once a laminated glass unit has yellowed, the damage is permanent. This is because the discolouration happens within the laminate.

The only solution is to replace the glass. This is one of the most compelling reasons to invest in high-quality laminated glass.

How to avoid glass yellowing over time

There are several ways you can help stop laminated glass yellowing over time. The best and easiest method is to specify high-quality laminated glass from a reputable manufacturer and ask for either a UV-blocking PVB interlayer or an SGP interlayer where appropriate.

This is your best bet, but it isn't always possible. If you have to make do with second best, you should protect the glass from excessive UV exposure. If this isn't possible, you can use external shading or UV-filtering films.

You should also keep the edges dry. Discolouration from moisture ingress typically occurs through edge damage or edge exposure.

For this reason, you should take steps to ensure the edges remain intact. You should also stop water from gathering around the glass, especially in balustrades, canopies and other external installations.

In terms of temperature, you should work to ventilate the glazing. Preventing heat buildup in this way can extend the lifespan of laminated glass.

Finally, you should use appropriate cleaning products for the glass. This means cleaning the glass with mild glass cleaners or soapy water and avoiding strong or abrasive solutions.

Taking these steps will mitigate the problem. But by far the best course of action is to start with high-quality laminated glass.

Founded in 1993, ToughGlaze is a UK-based glass processor that supplies some of the world's largest construction and architectural firms. If you need high-quality laminated glass for your project, don't hesitate to get in touch for a quick, competitive quote.