Here is the Visitation scene painted by Piero di Cosimo.
The inner field of the painting is a perfect square, flanked by narrow strips on the bottom and sides. The center of the square locates the clasping hands of the Virgin and Elizabeth.
The center of the square also defines a level, identified here with the orange horizontal, that describes the edge of the architectural platforms on which the small figures in the middle ground stand. From the ends of that horizontal, orange lines of 30-degree slope are now launched.
Then, from the points where those orange lines intersect the top of the panel, yellow verticals descend, which frame a yellow circle, in which a yellow square can be inscribed in a quadrature operation. Note that the bottom facet of the square aligns with the back of the platform on which the Virgin and Elizabeth stand.
The front of the platform corresponds to the bottom tip of a green equilateral triangle whose baseline corresponds to the equator of the square. A similar triangle above this equator helps to locate the heads of the two women as they lean towards each other, with their wimples sloped at 60 degrees from the horizontal. Their heads and the Virgin’s halo fit into the almond-shaped figure that circumscribes the paired triangles. One odd detail about this painting is that the horizon line of the seascape in the deep background between the women is not actually horizontal. Instead, it falls gently from left to right.
It is tempting to imagine that this might have been because the artist connected the wrong lines in his geometrical armature. Here, blue lines of 30-degree slope depart from the equator of the panel, within the red frame, and one can find the skewed horizon line quite precisely by connecting the point at left where the rising blue line intersects the yellow vertical with the point at right where the falling blue line intersects the side of the green triangle.
This painting is the property of the National Gallery of Art in Washington, DC.
This analysis was based on the image:
That image has now been superseded by: