The Ratchet
The tendency of coin inside the dwarven system, platinum above all and gold to a lesser degree, to pass into ingots.
The mechanism
Wealth accumulates, and Riches are for running costs. Within the dwarven system there is a kind of ratcheting: coin tends to move from Riches toward ingots. It is a tendency, not a policy.
Gold
A lesser ratchet works on gold. Dwarves think the right place for gold is in an ingot, but to them gold is an unexceptional metal that can serve as currency, since humans make extensive use of it. A dwarf with great gold Riches may be tempted to ingot a portion of them.
See also: Platinum, Wealth and Riches, Monetary Systems