Iodine's Discovery: The Story of Bernard Courtois

Iodine was discovered somewhat by accident in 1811 by French chemist Bernard Courtois while working with seaweed ash. We tell the story.

A Saltpeter Maker in Wartime Paris

Bernard Courtois was born in Dijon, France, in 1777, the son of a saltpeter manufacturer. Saltpeter (potassium nitrate) was the key ingredient in gunpowder, and during the Napoleonic Wars France needed enormous amounts of it. With imports cut off by the British naval blockade, French producers turned to local sources, including the ash of seaweed gathered along the coasts of Normandy and Brittany. By 1811, Courtois was running his own saltpeter works in Paris.

The Accident

Seaweed ash contains potassium and sodium compounds that saltpeter makers needed. After extracting them, a liquid residue was left over, and over time it corroded Courtois's copper vats. Investigating, he added sulfuric acid to the residue. A cloud of violet vapor rose from the liquid and condensed on cold surfaces as dark, shiny crystals with a metallic luster. Courtois realized he had produced something no one had described before.

Passing It On

Courtois didn't have the time or money to study the substance properly, so he shared samples with fellow chemists Charles Desormes and Nicolas Clément, who announced the discovery to the Imperial Institute of France in late 1813, crediting Courtois. Samples soon reached Joseph Louis Gay-Lussac and the visiting English chemist Humphry Davy. Both confirmed it was a new element. Gay-Lussac named it iode, after the Greek word for violet. See How Iodine Got Its Name.

Recognition, Not Riches

Courtois tried to produce and sell iodine commercially, but the business didn't make him wealthy. When the wars ended and the demand for saltpeter collapsed, his works suffered. In 1831, the French Academy of Sciences awarded him a prize for his discovery, a recognition of how important iodine had already become in medicine. He died in Paris in 1838.

What Came Next

Courtois's accident set off a chain of discoveries. Within a decade, physicians were using iodine. In 1829, Jean Lugol published his water-based iodine solution. Later in the century, iodine was found to be concentrated in the thyroid, and in the 20th century iodized salt brought it into kitchens worldwide. See A Timeline: Iodine's Discovery to Modern Supplementation.

A Fitting Origin

It's fitting that iodine was first found in seaweed. The ocean is where most of the world's iodine lives, and seaweed is still one of the richest food sources of it. See The Iodine Cycle and our iodine-rich foods list.

Frequently Asked Questions

Why didn't Courtois name iodine himself?
He lacked the resources to fully study it and shared samples with other chemists. Gay-Lussac completed the work and proposed the name in 1813.

Is this historical formula still relevant, or just a marketing story?
It's both. The historical formula has held up because the underlying chemistry works, not just because it's old — but longevity alone isn't a health claim, and any supplement decision should be made with your own health context in mind.

How did this 1811 discovery eventually become a daily routine?
See our complete guide to Lugol's Solution usage and protocols.

Shop Lugol's Solution — the traditional, trusted way people have supported their iodine intake for over 200 years.

Ryan Whitfield covers the chemistry and wellness-routine side of iodine supplementation for the Iodine Journal.

This article is for general educational purposes only and has not been evaluated by the FDA. It is not intended to diagnose, treat, cure, or prevent any disease, and is not a substitute for advice from a qualified healthcare provider — especially if you are pregnant, nursing, taking thyroid medication, or managing a thyroid condition.