#AskGlaston Episode 27: What is the root cause of a rainbow effect and how to avoid it?

This week, we are dealing with the two following questions:
1. Recently we got a complaint about 6 mm clear toughened glasses that were installed as hotel windows. The complaint was about a rainbow effect all over the areas. Can you help us – what is the root cause of this?
2. I’m running a PRISMASOLAR profiled glass and the structure of the glass is very deep. The glass always comes out sad, bending towards the structure on the top. How should I correct the problem?

For this week’s questions, see our full video response below! As always, remember to learn, share and succeed!

Recently we got a complaint about 6 mm clear toughened glasses that were installed as hotel windows. The complaint was about a rainbow effect all over the areas. Can you help us – what is the root cause of this?

This rainbow effect is called anisotropy. And every tempered glass has this kind of image. You can see this image with polarized filter e.g. sunglasses or sometimes even with naked eyes with certain light and conditions. With new tempering technologies like full convection you have tools to control and minimize the effect.

There are some excellent articles and presentations here in glastory so if you’re interested in the phenomenon you will find more about the phenomenon itself and also how to minimize it.

I’m running a PRISMASOLAR profiled glass and the structure of the glass is very deep. The glass always comes out sad, bending towards the structure on the top. How should I correct the problem?

This is a very challenging glass type. The challenge comes because there’s such a big difference between the surface area of the glass on top and on bottom. In this particular type of glass you have a lot more surface on top area, so that means that in the heating the top area absorbs the heating more – the more you have surface the more glass absorbs the heat. The same happens in cooling side but vice versa. You have much more surface area on top than on bottom so it also absorbs cooling more in the quench. If you’re running with very normal, standard settings it means that very easily your glasses will come out sad. So, to correct the situation start with the quench and adjust the air balance between the top and bottom pressure by increasing the bottom pressure. That’s the first thing and then you can also look into the furnace and look that the glass goes nicely into the furnace and adjust the heating settings if needed.

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