of about 8 minutes has been found to be optimal with the presently described batch sizes and equipment each batch should preferably be tumbled precisely the same amount of time as the batch before especially if the batches are to be matched or used on the same job or lot that is if three loads of stone nominally 400 pounds each are to be used for a particular job or are to be labeled as one lot number the amounts of stone and colorant should preferably be within about 10 of the actual desired values and preferably exactly the same or as close as possible and the amount of time that each load is allowed to tumble in the machine of fig1 should preferably be within about 10 and preferably precisely the same or as close as possible an automatic timer 13 see fig1 connected to the power supply for the mixing machine 10 is used to turn off the tumbler to control the tumbling time in an accurate manner the timer 13 could instead be wired into the motor drive circuit inside housing 18 for the drive motor for the ring gear 14 with commercially available equipment the stone can be colored in amounts of about 100 1200 lbs per batch as a practical matter this done in 50 or 100.