The following hopes to explain the role of slaves in Chaos Dwarf armies, needs a little improvement:
Treatise on Slaves
All slaves brought to the city must be declared to the Slaver’s Guild whether they are to be sold or not. Female slaves of a docile nature may be used as servents. Male slaves and females of sufficient fitness may be sent to the mines. Any slaves deemed unsuitable for work of any kind, either due to being unruly, weak or become too ill during service, should be sent to the Temple of Hashut for sacrifice. These rules are not hard and fast, some slaves fit into several categories.
All slaves of a fit nature must be given the option to serve in the armed forces to earn their freedom. Slaves which refuse this opportunity are unlikely to get any other chance at freedom, although some Lords have freed slaves under exceptional circumstances. A slave who serves a full 8 years is to be freed and given one month’s living expenses. A slave may choose to free another slave rather than themselves. A freed slave may not be recaptured during the month after they were freed. [Note: Only a tiny fraction of slaves survive their full term in the army].
Hope of freedom is a powerful thing and keeps slaves productive for far longer.