retorts are not for getting gold out of rock dust . but are used for burning off and recovering mercury .when used properly they are very effective ,and safely catch the fumes(mercury in it's gaseous state) -in water (not the atmosphere). most people do not use mercury for recovering gold ,but do find gold from time to time that has mercury on it . it does occur naturally -it is best to keep any gold tainted with mercury separate , as it will spread . when you have enough saved up - then retort safely to clean the gold ,recover mercury ----- then properly contain , and or dispose of.