A  painting from a reference photo for a pear cut to show the planes. Many art books talk about breaking down shapes into simple planes to help the artist see how light affects an object.  I have made a simple pear shape cut into basic planes for a practice aid to help beginning artists. The video shows the complete process of using this pear model to explore the process of painting  and object in light.

The Planes of a pear.
Find this reference material at my Etsy store with the link below.
https://www.etsy.com/ca/shop/RDMurrayStudio?ref=listing-shop2-all-items-count#items