OC is a form of tear gas, "Oleoresinum Capsicum" (oilresin of certain type of pepper). It is also known with name peppergas, even if it is not gas but just a "fog" or a stream of liquid. It is made from Cayenne pepper's (Capsicum Annuum) shiny cores, which look little like small carrots.
Oleoresin can be extracted from the dried and grinded pepper powder, so simple extraction could be done with normal coffee maker. One wanting to do such thing, would need to pour some pepper powder into the coffee filter and then run the coffee maker with little water and the final product in the jar will be (weak) OC.
Liquid OC-solution doesn't cause permanent blindness and the effect on nasal-, eye- and throat's mucous membranes vanishes after some 1/2 - 2h. Many researches confirm that pepper "fog" is superior in effectiveness compared to other chemical tear gases. Prolonged effects might be caused by some additional substance in the gas, possibly glyserol (which was used as additive in some old CN tear gas ampulles).
"Oosee", "PeTe", (online) http://www.guns.connect.fi/gow/kysvast3.html, ref. 20.6.2002