Here are some bust(sculpture) studies i worked on in my second year of college.
I worked on this project mainly to understand the various planes and plane changes which make a human head and also to study light and shadow. 
Time duration for each study was 2.5 hours.
I aspire to become a character designer so this was a very helpful project in better understanding the human face and has helped me improve a lot.
I thoroughly enjoyed working on this project and i hope you like it as well.