Found this old picture I did back in 2010 for school art thing.

Cant remember what was used but we all had to paint a sheet of paper with this purple stuff that turned brown, then i think used lemon juice or something to bleach sections, then drew the cow skull from one we had in the classroom. I don't recall the name of the chalkish sticks we used for the actual skull drawing. Forgot most of the stuff I did in school frankly.