No. Toughened glass cannot be cut, drilled, notched or edge worked once it has been toughened. If you try, the whole panel will shatter into small pieces. Every cut, hole and polished edge has to be made while the glass is still ordinary float glass, before it goes into the furnace.
Why it shatters
Toughened glass, also called tempered glass, is heated to around 620 to 700 degrees Celsius and then cooled very quickly with jets of air. The outer surfaces set first and end up squeezed tight, while the middle is held in tension. That balance is what makes the panel strong.
A saw, a drill or a glass cutter breaks through the squeezed outer layer and releases the tension inside. The energy is released across the whole panel at once, which is why it breaks completely rather than cracking where you cut.
How to tell if glass is toughened
- Look for the mark. Toughened safety glass made for the UK market is normally marked in one corner with the standard it meets, BS EN 12150, and often the maker's name. The mark is usually etched or printed and does not wipe off.
- Look through polarised sunglasses. Toughened glass often shows faint dark patches or stripes from the cooling process when viewed at an angle through polarised lenses.
- Check the edges. Toughened panels almost always have ground or polished edges, because raw cut edges are finished before toughening.
If you are not sure, treat it as toughened. Cutting the wrong panel is cheaper than an injury.
What to do instead
- Measure exactly. Measure the opening in millimetres at both ends and in the middle, and use the smallest figure. Allow for any gap the fixing system needs.
- Mark holes and notches. Give the position of every hole and cut-out from two edges of the glass. A simple sketch with dimensions is enough.
- Order it made to size. The glass is cut, edge worked and drilled first, then toughened, so it arrives ready to fit.
What about laminated glass?
Laminated glass made from ordinary (annealed) panes can be cut by a glazier with the right tools, because the panes are not under tension. Toughened laminated glass, where each pane has been toughened before bonding, cannot be cut. If your project needs both strength and glass that stays in place when broken, order toughened laminated glass to the exact size. Our guide on toughened or laminated glass explains which to use where.
Can it be re-annealed and cut?
In theory, a toughened panel can be heated slowly in a kiln and cooled very slowly, which removes the stresses and turns it back into ordinary glass that can be cut. In practice this is not worth doing: it needs specialist equipment, the panel can still break, and afterwards it is no longer toughened or a safety glass. It would have to be toughened again. Ordering a new panel at the right size is cheaper and safer.
How to give us hole and cut-out positions
A simple sketch is enough, as long as every feature is measured:
- Draw the panel and write the overall width and height in millimetres.
- For each hole, give its diameter and the distance from its centre to two edges, for example "from the left edge" and "from the bottom edge".
- For notches and cut-outs, give the width, the depth and where they start.
- Say which face is the front if the panel has a coating, a pattern or a printed side.
Holes that are too small or too close to an edge or corner weaken the glass during toughening. As a general guide, holes are usually at least as wide as the glass is thick and kept well away from edges and corners, but every job is different. We check your drawing before anything is made and tell you if a position needs to move.
Bought the wrong size?
If a toughened panel is too big, it cannot be trimmed. Your options are to adjust the frame or opening if that is possible, to use the panel somewhere else where it fits, or to order a new panel at the right size. If a panel is slightly too small, a different fixing or a wider bead may sometimes hide the gap, but ask your installer before you try it: glass that sits loosely in a frame is a safety risk.
When ordinary glass is the better choice
Not every job needs toughened glass. Picture frames, small cabinet panes and some secondary glazing are often made with ordinary float glass, which a glazier can cut on site. Where the glass is in a door, near the floor, overhead or likely to be knocked, use safety glass and order it to size.
Questions we are asked
Can I drill a small hole in toughened glass?
No. Any hole, however small, has to be drilled before toughening. Drilling afterwards will break the panel.
Can I sand or polish the edge of toughened glass?
Light cleaning of a sharp spot is sometimes done by professionals, but grinding the edge risks breaking the panel. Edges should be finished before toughening.
Can old toughened glass be re-cut for another use?
No. A toughened panel can only be used at the size it was made.
Can a glazier cut toughened glass for me?
No. No tool or method can cut toughened glass without breaking it. A glazier will cut ordinary glass, or order toughened glass to size for you.
Why is toughened glass more expensive than ordinary glass?
It goes through extra steps: edge work, drilling and the toughening furnace, all made to your exact size.
Ready to order? Send your sizes and hole positions for toughened glass made to size, or read how toughened glass is made.