Hash
Hashish can be expensive but like everything else in cannabis cultivation, it can be an investment that pays for itself. The small leaves surrounding the flowers, the "trim leaf" are usually coated in a large amount of trichomes, a leaf structure usually containing more THC than the flowers, that can be collected many ways, including dry sift(usually you should use a fine steel or silk screen), where plant material is rubbed against a screen that allows only trichome sized material through. Put a mirror under the sifting device to catch all the trichromes or "keif". You can also use Bubble Bags or other kinds of filter bags. With this method, trichomes on trim leaf are frozen for 24 hours then agitated in ice water in a 5 gallon bucket lined with a succession of bags having decreasing screen sizes that capture the plant matter and allow the trichomes to pass down to the bottom bag where they collect into a wet paste. The large fan leaves may also have a minor amount of trichomes to be collected. The paste is pressed between its screen and a clean absorbent towel to extract water from the paste until it has the texture of clay. The clay (hash) is then shaped and smoked. This type of processing creates hashish called "bubble hash". The dry sift and so-called "bubble bag" methods can also be combined in a very efficient dry-ice sifting process; the leaf material is thrown into a bubble bag (or otherwise properly sized silk screen bag) with dry ice. The bag can then simply be hand shaken over a mirror to obtain a very pure concentration of trichomes. These can be stored as is or subsequently pressed into "blonde hash".
"Bubble hash" is so named because of bubbles released (sometimes) as it burns. Pre-freezing the trim for 24 hours reduces bubbling by stiffening and hardening the trichomes. This prevents the trapping of water molecules when the trichomes separate from leaf matter (imagine icicles breaking off a frozen tree branch). The lack of using pre-frozen trim reduces the quantity of trichome separation and it increases the likelihood of "burning bubbles". These bubbles are interesting to see but totally harmless.
Hash is generally more potent than the flowers from the same plant.
Read more about this topic: Cannabis Cultivation, Harvesting, Drying and Curing