Prussian blue was discovered accidentally in 1706 as a failed attempt to make a red pigment

Prussian blue — ferric hexacyanoferrate — is generally credited as the first modern synthetic pigment, and its discovery is a canonical accident. In Berlin around 1706, the paint-maker Johann Jacob Diesbach set out to make a red cochineal lake pigment. He finished the batch with potash borrowed from the alchemist Johann Konrad Dippel; that potash was contaminated with Dippel's "animal oil," a bone/blood distillate. The reaction produced a deep blue precipitate rather than the intended red: "Diesbach was attempting to create a red lake pigment from cochineal, but obtained the blue instead as a result of the contaminated potash he was using."

The core of the story — Diesbach, Berlin, ~1706, a cochineal red gone wrong yielding iron ferrocyanide — is standard chemistry history. Dippel's specific role, however, is weaker: the source article itself notes the detail is not corroborated by other historical accounts, making the "borrowed contaminated potash" attribution folklore-adjacent even where the accidental-blue outcome is well attested. The single source here is Tier 4, so the biographical particulars remain provisional; independent verification against a primary or scholarly history is tracked in question-verify-prussian-blue-1706-accidental-discovery-primary.

The claim sits in the vault's recurring pattern of consequential accidental discoveries — compare claim-chest-compression-cpr-discovered-by-accident and claim-kouwenhoven-electrocution-research-produced-defibrillator, where an unintended observation became a durable technique. The pigment's afterlife is where it turns cross-domain: the same 1706 compound is now an FDA-approved radiological antidote. It also sits adjacent to the vault's other pigment-and-color chemistry, such as claim-kubelka-munk-theory-devised-1931-for-paint-opacity.