Related to the ray tracing materials, I taught a two-day crash course on writing a ray tracer. The materials are available online: https://avik-das.github.io/build-your-own-raytracer/
Peter also uses area lighting derived from the surroundings, whereas my implementation uses point lights that result in sharp specular highlights. There are no surroundings in my image, only the lights.
No doubt Peter's materials look great. I wish I had time to cover more in my course, but I wanted to make sure I covered the prerequisite vector math as well for students without strong mathematical backgrounds.