Quicklime

There was an actual medieval profession of lime burner, who burned calcium-rich minerals such as limestone, chalk, marble, or even sea shells. This was done to produce quicklime, which had a lot of useful properties. Dying, tanning leather, making soap, producing fertilizers, concrete—all used calcium oxide, called "quicklime."

The name, first seen as quyk lym in the late 1300s, comes from Latin calx viva, "lime quick"—using "quick" in the older sense of "living" because it was such an active substance. The ancient world discovered its usefulness for mortar (after being mixed with water to make a slurry). Limestone blocks of the pyramids have quicklime plaster. Rome used quicklime for construction extensively, and it is even found in the Great Wall of China.

The Ancient World also used it as a weapon in warfare. Powdered quicklime could be catapulted at enemies; its irritability in a person's eyes made them easy prey when the attacker engaged. Enough quicklime coming into contact with enough water could cause severe burns. King Henry III of England's (1216 - 1272) navy destroyed a French fleet by blinding the sailors with quicklime. (This was always a perilous gambit, since the wind might blow the power back to you.)

In the Middle Ages, when coal mining became cheaper and more widespread in the 12th century, burning to make quicklime was easier. It was used as mortar, plaster, for floors, and in frescoes.

One mis-use of quicklime in the Middle Ages was with corpses: it was thought to speed up decomposition, so sprinkling quicklime liberally when one needed a mass grave (after warfare, or in some responses to the Bubonic Plague) was thought to be efficient. It was also supposed to "sterilize" cesspits and counteract diseases they might engender. The truth is, however, that quicklime is actually a preservative; small amounts are sometimes used in flour to increase its acidity and act as a preservative and a leavener. Quicktime can cover the stench of decomposition, which may be why people thought it "got rid of the corpse" faster.

For many years I have read how Roman concrete became harder and more durable over time, defying logic. Very recently it was discovered that quicklime was the reason for its "self-healing" nature; here's a link to learn more.

I wanted to include a link to the reference above to Henry III, and I've discovered that I have mentioned him many times over 1263 blog posts, but have never given him his own entry. I'll will fix that oversight next time.