 Bismuth is used to make free @-@ machining steels and free @-@ machining aluminium alloys for precision machining properties . It has similar effect to lead and improves the chip breaking during machining . The shrinking on solidification in lead and the expansion of bismuth compensate each other and therefore lead and bismuth are often used in similar quantities . Similarly , alloys containing comparable parts of bismuth and exhibit a very small change ( on the order 0 @.@ 01 % ) upon melting , solidification or aging . Such alloys are used in high @-@ precision casting , e.g. in dentistry , to create models and molds . Bismuth is also used as an alloying agent in production of malleable irons and as a thermocouple material . 
