Homebrew PCBs

A while back, Adam Seychell mentioned the following: 
 
>If you decide to make some ammonium persulfate then it doesn't 
>require or use dangerous chemicals at all, just boring old ammonium 
>sulfate, the stuff for fertilizing your garden.  
 
I haven't had any luck looking through the files or Googling up any 
specifics on the process though. If someone could provide details, 
I'd certainly appreciate it. 
 
Thanks, 
Stan