Hash, or hashish, has been made for centuries. But using ice water, agitation and filtering to do so is relatively new. Here’s how “bubble hash” (a cannabis concentrate comprising countless trichomes or resinous glands) is made. First you need some cannabis. Then you.agitate the cannabis in ice-filled water. Think of the way that clothes are agitated in the washing machine with soap to remove dirt – During this process of agitation the resinous trichomes freeze, then break off and finally separate themselves entirely from the rest of the plant matter. By passing the captured trichomes suspended in the cold water through a series of ever-finer mesh screens (at the level of microns) producers can maximize potency and purity (in terms of removal of all unwanted plant matter) from the extract – in this case bubble hash. When the end result, which looks like powder, is heated and compressed, the bubble hash becomes a sticky substance called rosin. The reason this is so fascinating to many cannabis historians is the fact that ice, as opposed to cannabis, is a relatively new invention.