What metaphors are used in The Truth: A Novel of Discworld by Terry Pratchett?

William's life changes when a cart runs him over in the street and he is rescued by dwarves who run a print shop. The novel opens with rumors running wild that the dwarves have discovered how to turn lead into gold. This is a process that has eluded alchemists and magicians. William realizes that it is a metaphor for typesetting where the lead slugs that are aligned into rows and pages sell newspapers to a society hungry for news or "olds," since people want to learn about things in which they already believe.