I found this great video on Scrap Time of Tim Holtz showing "how to blend and shade" with Distress markers.
He also addresses the frayed marker tips and said all you do is remover the tip turn it around and insert the other end and you have a new tip .
Scrap Time - Ep. 790- Tim Holtz share tips for Blending Distress Markers! on Vimeo
I don't have these markers but I have read that several people are having trouble blending and shading with them so I thought it may help people to post this .