Slave Currency by Mike Jenkins

Copperopolis:
once empire of that metal,
precious as coal and iron,
as Rhondda to one
and Merthyr the other

ingots, cable and sheeting
smelted and carefully crafted,
a valley mapped by workings ;
companies growing with every ship
whose flags whipped above waves

but manillas, slave currency,
seem like bracelets
or good-luck horseshoes,
coins which clasped fast
and weighed out wealth

30 manillas = one man :
from furnace-heat of African sun
to holds where they were rolled
and beaten and marked,
or thrown away like impurities

now these have lost their colour,
become dark as if tainted
by the hands that traded them
and resemble manacles,
blood staining away any shine.

(Swansea Industrial & Maritime Museum)
http://www.mikejenkins.net/