First, thanks to all those responded. this forum has been great whenever I needed answers.
so the famous artists do it too, i.e. paint over their existing paintings.
I do know about not using acrylic gesso over oil, that's why I am asking this question for oil painting. these are nice canvases, gallery wrapped and good sizes (at least 24"x24" and larger.) I just couldn't bring myself to throw them out. though it'll probably be the easiest thing to do.
I paint with some texture, definitely not flat. The paint on these paintings have been at least 2 years old, so I think they're more likely dried and cured.
painting on the texture of previous painting may sound interesting, but I think it'll confuse me so much I couldn't concentrate on the current painting. maybe I'll try the sanding then titanium white with little oil. should I do 2 layers? or more?
also, I was searching on dickblick. and I found a Winsor Newton oil painting primer http://www.dickblick.com/products/wi...inting-primer/
and a Gamblin oil painting ground http://www.dickblick.com/products/ga...inting-ground/
has anyone tried these previously? are these oil based thus ok to use over oil paint or are they for first time canvas priming?
again, thanks for all your help!