Legends often paint underground kobolds as evil creatures. In medieval mining towns, people prayed for protection from them. They were blamed for the accidents, cave-ins, and rock slides that plagued human miners. One favoured kobold prank was to fool miners into taking worthless ore. For example, 16th-century miners sometimes encountered what looked to be rich veins of copper or silver, but which, when smelted, proved to be little more than a pollutant and could even be poisonous. These ores caused a burning sensation to those who handled them. Miners tried to appease the kobolds with offerings of gold and silver and by insisting that fellow miners treat them respectfully. Nevertheless, some stories claim that kobolds only returned such kindness with more poisonous ores. Miners called these ores "cobalt" after the creatures from whom they were thought to come. In 1735, Swedish chemist Georg Brandt isolated a substance from such ores and named it "cobalt rex". In 1780, scientists showed that this was in fact a new element, which they named "cobalt".