It is necessary that I "mask" out the eye glasses on 2 of these drawings so that I don't accidentally paint over them. In the photo, I show you the brand I like to use because it doesn't leave a yellow stain on the paper when I rub it off. Once I apply it, the clock start ticking. I cannot leave it on the paper for longer than 4-5 days or it becomes permanent. Yikes.

I am also showing you the tool I used to apply the fluid. If the area to be covered is large, I used a brush. But here these small metal tools are great. And I don't have to clean them like a brush.