I just tried my first interpositive for my first 8x10 neg for a Van Dyke. Rather than make an 8x10 interpositive, I contact printed my 4x5 neg to some 4x5 Ilford Ortho film. The interpositive was VERY low contrast - even less than my negative. When I enlarged the 4x5 positive to an 8x10 Arista Ortho sheet, it gained N+3 maybe. Then in the Van Dyke process printed with lots of sparkle but blown out highlights. The image was fine for this but I can see there is lots of room for technique.