Ronny,
I haven’t seen anything here in a while, what’s going on with your tutorial?
Also, I have started doing my first work with whitened fossil photography for a potential paper I am working on. Hopefully this will work out well. I am using the ammonium chloride method I described in an earlier post. This coating washes off with water. Your MgO method would be easier in some ways but having to brush off the coating could damage the fossils I am working with.
Jack