It is painful to read of your quest for highlight detail in con-tone carbon printing. While many will come forward with advice the sad truth is that carbon prints have a well-documented problem with the loss of highlights (see the 11-17-11 APUG Post: Highlight Loss in Carbon Printing) This can easily be seen when printing a step wedge, but most carbon enthusiasts print "pictures" and are satisfied with the results of their efforts.

Charles