How to distinguish the tin side of float glass

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How to distinguish the tin side of float glass

Made by floating molten glass on a bed of molten metal, float glass is made most commonly from soda-lime glass and has a uniform thickness and a very flat surface. You will find most modern windows are made from float glass.

Tin is the most common molten metal used to manufacture float glass. It leaves a residue on one side of the glass panel which you can’t see with the naked eye, but can be identified with a short wave UV light. The tin side often needs to be identified as it will react when fired or with some paints and enamels.


A UV lamp with a shortwave UV is required to image the tin or ‘float’ side of glass. Two popular portable lamps for this application are the UVG-4 mini UV lamp 254nm, AA battery powered unit, or for a more intense portable lamp the UVS-26P features 2 x 6-watt shortwave UV tubes which can be used separately or together.

The method for distinguishing the tin side: Turn your main room light off and roll the UV light across  the edge of the glass shining the light along the front and back side of your glass. You will see that the tin side of the glass will float will glow, and the other side will not. Read the safety instructions before using your UV light as you should not look directly into the light.

For more information on the UV lights available please get in touch with one of our technical team on 01954 233 120, email or fill in the below contact form.

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