This unsatisfactory result normally occurs when you avoid stretching the paper. So the best thing to prevent it from happening is to stretch paper from the start. If it is too late to do so and you have already finished the painting but it is uneven. There few ways to remedy this. Very common way involves wetting the paper from the "wrong" side/ the under side. The way that worked for me: 1. Make sure that the finished painting is COMPLETELY DRY 2. Choose a clean board and cover it with a clean large sheet of cartridge drawing paper, preferably larger than a painting itself. 3. Place the board with a clean sheet of paper on a suitably flat surface (floor, large table etc) 4. Place the finished painting FACE DOWN on the prepared board (covered with a clean sheet of paper). 5. Using a pump-spray (spray not too fine and not too heavy: usually pumps used for hair products are suitable) wet the WRONG SIDE of the finished painting. 6. Work in the water gently with a soft hake brush (or other large soft flat brush). Let the paper to expand. Make sure that you do not let the water to run under the edges of the painting and cause backruns on the finished painting. 7. Take a second sheet of clean cartridge drawing paper (of the same size as the one you covered the board with, it should be larger that the painting itself) and cover the paiting's WRONG SIDE. You ended up with your painting being "sandwiched" between 2 sheets of clean cartridge drawing paper. 8. Now take as many large-sized heavy books as you need and put them evenly on the board. Make sure that you distribute the books in such a manner that they cover the whole area of the painting, and none of it ends up not being pressed. Covering the whole board is even better. 9. You have created a very primitive version of a press. Now leave it to dry for about 40min-1hr. DO NOT PEAK ! LEAVE IT ALONE! Of course you might come across other ways to do it. But this one worked for me very well.