Tempers raised

Colin Madelin continues the theme of tempering springs. Gunsmiths achieve an even temperature by immersing the hardened spring in molten lead (350°C) so that it reaches a purple/blue colour. Temper can be varied by adding 50/50 plumber’s solder or 60/40 electrician’s solder (60% tin, 40% lead).

A known melting point gives an accurate temperature guide