Gumroad - Secrets of Shading

We begin with diagrams and exercises to help you understand shading and rendering as "drawing on the inside" of dimensionally conceived forms, and move on to several practical demonstrations.
The demonstrations are done with pencil and provide insight into working with graphite, but the concepts are applicable to all media. The videos total five hours of content and all chapters are fully narrated. All videos are 1080p full HD.
Here is a list of the chapters contained in this tutorial:
1- Light on a basic sphere and intro to compression (~33 minutes real time)
2- Point and soft light sources (~13 minutes real time)
3- Light on elliptical / lozenge shapes (~25 minutes real time)
4- Light on complex organic shapes (~40 minutes real time)
5- Tentacle demo 1 (~25 minutes real time)
6- Tentacle demo 2 (~45 minutes real time)
7- Two arm demos (~1 hour real time)
8- Full figure demo (~31 minutes sped up with voiceover)
9- Bonus World Tree process (~15 minutes sped up with voiceover)
Homepage

https://gumroad.com/stevenzapata#iuUJK