England's Trial of the Pyx stopped mints from grading their own coins

The medieval English mint produced the coinage the entire kingdom's economy depended on, and debasing that coinage — cutting corners on weight or metal purity — was both a real temptation for whoever ran the mint and a real risk if it went undetected, since bad coin degraded trust in money itself across the realm. Simply asking the mint to self-certify its output solved nothing: the mint had every incentive to report its own coins as sound whether they were or not, and no outside party had visibility into what was actually being struck.

The crown needed a way to verify coin quality that didn't depend on trusting the very institution being checked, but auditing every coin as it was struck wasn't practical either. What was needed was a sampling and custody system robust enough that no one, including the mint itself, could tamper with the sample between production and inspection.

Starting with the first recorded public trial on 24 February 1248, and formalized by a 1279 ordinance under Edward I, England set aside a sample coin for roughly every ten pounds of silver minted throughout the year, sealed inside a locked box called the pyx, with custody split between different officials so no single person held every key.

Removed the mint from grading: sealed sample coins in a multi-custody pyx, and independent goldsmiths assayed them, so no one with a stake judged the outcome.

Sealed multi-key box prevented tampering between production and inspection.

Independent goldsmiths had no incentive to pass bad coins, unlike the mint.

Personal consequences for the Master of the Mint made quality proactive, not just reported.

When an entity certifies its own output, separate sampling and grading from it, using sealed custody and independent graders with no stake.

The system caught real failures over the centuries — even Isaac Newton, as Master of the Mint, was called to account under the Trial in 1696, though he was able to demonstrate the fault lay elsewhere — institutionalizing coin quality assurance as something the mint could never simply assert about itself.