How gold bars are made

The big bars in central bank vaults weigh about 12.4 kilograms and are poured, not stamped.

stations: 6
things upstream: 12
raw sources: 7
steps from the ground: 4

The short version

Refined gold, commonly 99.99% pure, is melted and poured into a mold, where it cools into a cast bar with rounded edges. The bar is cleaned, weighed and inspected before its maker, weight, purity and serial number are stamped on. Minted bars take another route: molten gold becomes a long flat strip, blanks are cut from it, and engraved dies strike each one under high pressure.

Melt refined gold

Gold from mines or recycling, refined to at least 99.9% pure, is melted ready for casting.

Goes in
Gold
Pour into the mold

Molten metal goes into bar-shaped molds and is left to cool. Some plants instead run it through a graphite die into a continuous strip, the starting point for minted bars.
Clean and weigh

The cooled bar is cleaned and weighed. Its surface keeps the individual marks of the pour.
Strike the minted blanks

Blanks cut to exact size from a flat strip go between engraved dies, which strike them under high pressure and leave crisp detail.
Stamp the marks

Manually or on an industrial press, the bar gets the maker's hallmark, weight, purity and often a unique serial number.
Assay and seal

Weight, dimensions, purity and surface finish are verified. Many bars then go into tamper-evident packs with an assay certificate.

End of the lineGold bar

Worth repeating

The standard Good Delivery bar held by central banks has a nominal weight of 400 troy ounces, about 12.4 kilograms.
A Good Delivery bar must be at least 995 parts per thousand gold.