A painting I did a while ago now has a crease up the middle which has caused a white vertical block about three quarters of an inch across. I think the only thing to do is to cure the crease by getting the paper flat again. Could the paper shomhow be ironed from the back? I don't want to immerse the painting in water, which is how ou would stop a fresh sheet of paper from creasing.

It is very annoying when something like this happens. However, if the crease isn't too bad, the following method may help to alleviate the problem. Lay the painting face-down on a clean surface and brush along the crease with a wet watercolour brush to relax the paper fibres. Still working on the back of the painting, gently press the fold down with you fingersover the protective covering of a paper towel until the paper lies flat. Dry the painting between sheets of blotting paper with some weight on - don't be tempted to hasten the procedure by ironing as this may cause cockling.