The two major processes of hardening and tempering can be broken down into four major steps. First, a piece of carbon steel is heated gradually until it reaches a temperature above the alloy's critical temperature. The steel is then quenched, usually in water or oil (though other quenches, such as brine or
sodium hydroxide solutions, are sometimes used to achieve a particular result). The steel is now at that given alloy's maximum hardness, but as stated above, also brittle. At this point, tempering is usually performed to achieve a more useful balance of hardness and toughness. The steel is gradually heated until the desired temper colours are drawn, generally at a temperature significantly lower than the alloy's critical temperature. Different colours in the temper spectrum reflect different balances of hardness to toughness, so different temper levels are appropriate for different applications. The steel is then re-quenched to 'fix' the temper at the desired level. A talented smith or metalworker can fine-tune the performance of a steel tool or item to precisely what is required based solely on careful observation of temper colours. A visual representation of this process may make the concept easier to understand. made of hardened steel. ==Testing for hardened steel==