It's not something I do very often, but when I do, I feel like I'm risking a whole piece with a technique where I'm guessing.
I have done the slicing off a layer of paper with a curved razor blade - when this works, it works brilliantly, but I've also sliced the paper too thin and cut myself a bled on a piece!
I've done the scraping off with a scalpel - but can't achieve anything like a smooth finish to the corrected paper.
Today I tried 2 techniques :
1. "Unpainting". Because I generally use gouache which is water soluble, I had a try at using a just-damp brush to wet the gouache and lift it with the brush. After each time of doing this I dabbed it with a clean kitchen towel.
You can see that although it's far from cleaned the letter off, it's removed a great deal of the dense colour.
While I'd hope I never have to do a correction ever again (!) I do feel a little more confident about it now.
And here's an image of the white space being written on - no feathering - perfect.
The paper is from Artesavers - here : it's the one I was having fun with in the post on giant paper - here.
Hope you found that helpful!