The ring stacks multiplicatively with Goldsmith gauntlets when smelting (2.5*1.5 = 3.75 times normal experience), yielding 84.3 Smithing experience per gold ore. However, it only stacks additively with the Goldsmith gauntlets when superheating (+50% from the ring plus +150% from the gauntlets = +200%, or 3 times normal experience), yielding 67.4 Smithing experience per gold ore. The smithing ring and sacred clay hammer will not stack when smithing regular bars into items, however, they will when making dwarven burial armour as long as the ring is equipped or in your inventory and the sacred clay hammer is in your inventory. The sacred clay hammer bonus is used in addition to the clan ring bonus.