Frederick Arnall   Son of a fugitive alderman from Cornwall my grandfather Fred took up the shovel in his early teens to extract khaki alunite   from an upside-down mine tunnelled inside a mountain and send it cascading down into commerce as alum, the medicine that fixed colours in cloth.   Marrying, he moved south to dig refractive coal, tarry fossil rock that still powers half our world and wrecks lung tissue. Did his, dead at fifty. Wish we’d met.   Irony of coal, how it synthesized Nature’s hues. Irony of his tallness that raked him, and of his deep…