If you mix graphite carbon and boron 10 % and take it to 1000 degrees C with a constant pressure of 100 tons per sq inch through out the heating AND cooling process ?

That sounds like the basic process. There are catalysts involved, I believe, and I have no idea if that is the right amount of boron to use. Sounds easy, doesn't it? Its not. There is a synthetic diamond factory about 10 miles here and I understand there are many, many pounds of off spec diamonds buried in the foundations of the presses.