#AskGlaston Episode 44: Why I can’t get rid of the vertical lines visible on my wine closet doors?

This week, we are dealing with the following question:

Why there are vertical lines visible in certain light on my tempered-glass wine closet doors?

For this week’s question, see our full video response below!

You can see in the photo attached that there are some vertical lines in my non-cooled wine closet doors, which are tempered glass. Each door is 8 1/2 ft by 3 ft and 3/8 inch thick. The lines are visible in certain light and with polarized sun glasses. I tried cleaning them but they don’t come off and the glass seems clean. With my fingers, I cannot make the horizontal scuff marks across these vertical lines. It looks like someone was cleaning them up and down in a sloppy way. Any thoughts?


The lines that you see on the photo are typical for tempered glass. These are caused by the process itself, and the phenomenon is called anisotropy or iridescence.

This phenomenon was getting more and more attention over the past few years. And we have also quite many articles already here in Glastory about it. So if you want to know more about anisotropy, make also sure to check those articles out.

But in short, what is causing this issue is the tempering. It is basically impossible to achieve 100% even cooling and heating in the furnace and in the chiller. And this is causing a very small stress differences inside the glass that become visible under the polarized light.

Anisotropy is exactly what you see on the photo. So unfortunately, it is basically impossible to get rid of the lines because it is something that is not on the glass but rather inside the glass.

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About the author

Riku Färm

With a background in industrial engineering and management, Riku is Director of Heat Treatment Product Management & Sales Engineering at Glaston. He is keen on working with customers and developing new business- and technology-related things – which makes product management a natural fit for him. In everything Riku does, he aims to ensure that glass processing customers are as successful as possible. This drives Riku and challenges him every day to think about what could be done better. Riku is an e-sports enthusiast. Aside from watching, he also enjoys playing the games that he actively follows.

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