Possible Questions:
- Harden
- Toughen
- Temper
- Strengthen
- Temper, as metal
- Temper, as steel
- Temper steel
- Strengthen by tempering
- Heat and cool, to strengthen
- Treat, as glass
- Treat with heat to toughen
- Toughen, as steel
- Toughen, as glass
- Toughen or temper
- Toughen glass
- Toughen by heating, as glass
- Temper.
- Temper, as glass or steel
- Temper, as glass
- Temper or toughen
- Strengthen, as glass
- Strengthen by heating and cooling
- Strengthen and temper
- Heat-treat
- Heat to remove stress from, as glass
- Heat to prevent stress
- Heat and then cool, as glass
- Heat and then cool
- Fire in a kiln