I did print a few scales/wedges with vandyke, trying to see what my "usual time" showed as a grad scale. Turns out that my "favourite" time for max shadow density on quite a few of my negs is 4:20, but at that time the shadows on the wedge are almost completely blocked up... about half the scale is "black".
On the other hand, if I reduce the exposure one stop (2:10) I get a beautiful, almost continuous scale, but I don't get the density and deep black/brown I have when I expose more...
Is there a trick, or do I have to live with it ? I double coat the paper of course...