Today I worked all afternoon and painted the whole shell and background again. Above you see the result. It is much better than before. I used iridiscent medium for the paintings on the shell, you see it on the palet below in a curl. The other white stuff is a medium for making the paint transparent.
Now I am doubting whether I will change some shades and/or will finish the painting with shiney varnish or not. Then I can finally add the Fibonacci-lines with iron wire.