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Tempered (or toughened glass) has been specially processed using thermal or chemical treatments in order to improve its strength. One important function of tempered glass is that it shatters into tiny fragments when broken, instead of sharp shards. You may be required to smooth the edges of the tempered glass, especially if it is bare and therefore posing a risk to health--sharp edges can result in deep lacerations, which can leave the body prone to blood loss and infection.
Wear safety goggles to protect yourself from the remote possibility of flying pieces of glass; also wear thick gloves as you will initially be handling sharp edges.
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Lay the glass down on a hard, flat surface which will provide it with a stable platform upon which you can work.
Use a whetstone to soften the glass by simply running it along the edges of the glass. Do not apply too much pressure, but remain firm and even.
Use a damp cloth to clean the edges of your glass.
Always anneal tempered glass before cutting it.