Wrought iron
Wrought iron which had been faggoted twice was referred to as "Best"; if faggoted again it would become "Best Best", then "Treble best", etc. Faggoting stretches chemical impurities within the metal into long thin inclusions, creating a grain within the metal. "Best" bars would have a tensile strength along the grain of about 23 short tons per square inch (317 MPa). "Treble best" could reach 28 short tons per square inch (386 MPa). The strengths across the grain would be about 15% lower. This grain makes wrought iron especially tricky to forge, as it behaves much like wood grain—prone to spontaneous splitting along the grain if worked too cold. Wrought iron, especially less refined iron, must be worked at or near a forge welding heat, that is incandescent and white in color. In old, very rusted pieces of wrought iron, the grain is revealed, making the iron bear a striking resemblance to reddish-brown wood, and if it is rusted into the grain too deeply, it will need to be refined once more before reforging it.