BHO (Butane Hash Oil) is the result of the process involving gas passing through a pipe full of marijuana. The low temperature of liquid butane crystallizes cannabis resins. While butane crosses the tube, the crystallized resin is trapped into the liquid gas. What remains is just the crystallized resin by quickly evaporating the gas. It is usual to pass the product through a vacuum chamber to give it a characteristic texture. This process should always be performed in ventilated locations and away from any electrical appliances or flame. The gas must be as pure as possible.