I am into my 3rd year of humanure composting. A year and a half ago, when I first heard about the wonderful traits of terra preta I had been stockpiling our humanure for 6 months in a 5 by 5 foot compost pile starting with 18 inches of spongy hay as a buffer between soil and "nightsoil". At the halfway mark of the year I added to the pile between contributions aproximately 1 inch of charcoal salvaged from woodstove ashes given me. I am sure this is a rounded up number as most pieces were smaller than than 1 inch and spread only one layer deep. After the year of contributions the compost pile is left to (actively) rest another year. I broke into the pile for the first time in march 2007 a few months earlier than ususal as we are are preparing to move and I was anxious to use it for summer crops. When I got to the middle of the pile there was a rich 4 inch thick layer of black compost. Wish I had a camera to record the proof that thermophilic bacteria spread the breakdown product inches a year.
Meanwhile have I become skilled at charcoal making and now have test plots in the garden, with humanure and/or charcoal(crushed), added to garden rows... hoping to get a nice camera to share pics with fellow char enthusiasts.