3–4 weeks. Then the lichen is dried and ground to powder. Cudbear was the first dye to be invented in modern times, and one of the few dyes to be credited to a named individual: Dr Cuthbert Gordon of Scotland: production began in 1758, and it was patented in 1758, British patent 727. John Glassford invested in the new process with funds from his slave-owned tobacco business by establishing a dyeworks in Dennistoun in 1777. The manufacture details were carefully protected, with a ten-feet high wall being built around the manufacturing facility, and staff consisting of Highlanders sworn to secrecy. The lichen consumption soon reached 250 tons per year and import from Norway and Sweden had to be arranged. A similar process was developed in France. The lichen is extracted by urine or ammonia, then the extract is acidified, the dissolved dye precipitates out and is washed. Then it is dissolved in ammonia again, the solution is heated in air until it becomes purple, then it is precipitated out with calcium chloride. The resulting insoluble purple solid is known as French purple, a fast lichen dye that was much more stable than other lichen dyes. Gallery See also Litmus test Ethnolichenology References External links Orchil, the poor person's purple Natural dyes Histotechnology Food colorings Staining dyes PH indicators Oxazines