Step into a Victorian parlor drenched in a brilliant yellow-green: wallpaper, upholstery, dresses, children's toys. Every surface is shedding arsenic. This episode explains how Swedish chemist Carl Wilhelm Scheele created the pigment in 1775 by dissolving arsenic oxide in boiling sodium carbonate, reacting it with copper sulfate, and heating the precipitate to 158 degrees Fahrenheit to lock copper and arsenic into a vivid crystalline structure. Because earlier copper carbonate greens faded to brown, the new stable color went viral in textiles, candles, book bindings, and even a green blancmange dessert.

The hosts follow the slow recognition of the danger, from confectioners in Greenock, Scotland whose customers learned to fear green sweets, to the 1861 death of 19-year-old artificial flower maker Matilda Scheurer, whose eyes and fingernails ...