I use a lot of images in my classes, especially art and architecture from the time periods we’re studying. It can be challenging, when studying architecture, to visualize a 3-dimensional structure when all you’re looking at is a 2-dimensional photograph. One way of meeting this challenge is by learning to read different kinds of 2-dimensional representations, like ground plans and elevations. Another way is to use 3-dimensional models. And sometimes you can make your model out of produce.
When I teach Renaissance art in a core course on modern Europe, I choose three examples, one each of painting, sculpture, and architecture—all from Florence, all from about 1430, and all one of the first of their kind. So we take a look at Donatello’s David, the first free-standing bronze nude since antiquity;Masaccio’s Holy Trinity, one of the first uses of vanishing point perspective; and Brunelleschi’s Pazzi chapel, an early example of a domed building modeled on the Pantheon.
Masaccio, The Holy Trinity 
Donatello, David 
The Pazzi Chapel
Unlike the Pantheon, however, where the dome sits atop a round drum, Brunelleschi’s dome sits on a square base. The transition is achieved by means of pendentives, the curvy triangles on either side of the semicircles. This is extremely hard to visualize from a photo alone—so I bring out the grapefruit. I owe this demo to my college art history professor at Santa Clara University, Dr. Brigid Barton (one of my pedagogical role models).
Take one grapefruit, the largest and roundest you can find, and slice it in half. You now have two hemispherical domes; set one aside. Then, with the cut side down, make four vertical cuts in the shape of a square. And voila! You now have a square base transitioning to a round dome, by means of pendentives. Thanks, Dr. Barton!
