To my knowledge you spray a fem plant with colloidal silver every day for a week before flowering this causes the bitch to produce ball sacks. Any bud that gets fertilized with those pollen sacks produces female seeds. Make sure your colloidal silver is .999 pure you can google colloidal silver and how to make it and supposedly it can be done with 40 dollars worth of stuff from ebay. NOTE: I've never done this, its just the general consensus I got after a couple minutes of google time.