I always feel that if you start a w/c painting, it has to be finished in one fell swoop. Now, I'm asking....can you start a w/c today, and maybe finish it tomorrow or the next day? Won't it change the pic by drying out....or do you just 'rewet' it without taking the color away? Won't it change the effect you are trying to achieve if you leave it, then pick it up? I'm confused. Guess that's why I get in trouble...I try to work too fast to get it done.