The Makers Mark
A finished ingot tells a story about its manufacture and value. The sunken area in the center of the top of the ingot resulted from the shrinking of the gold as it cooled; the center shrank more than the sides because it took longer to cool. When molten gold is poured into a mold, other minerals in the gold dust combine to form glass on the surface. Ingots often carry marks from hammer blows used to remove the glass. The ingot's rust-coated surface is the result of the corrosion of the steamship's enormous engines and boilers. The gold itself does not corrode; the rust is only a surface deposit. The missing corner shows that an assay sample has been cut for chemical analysis. The assayer would have cut the other corner for his commission.
© AMNH / Rod Mickens
The Eureka Bar
This is the largest surviving assay ingot from the California gold rush period. It weighs 30 kilograms (80 troy pounds). Its worth in 1857 is stamped on the bar--$17,433.57.
It sank, along with three tons of gold, in the hold of the S.S. Central America. If it had reached New York, it would have been melted down and then minted as United States gold coins.
Ten miners would have worked for three years to gather enough gold to make the Eureka bar.