⚠The manuscript is written entirely in Leonardo da Vinci's characteristic mirror-script (right-to-left). Some ink bleed-through and fading are present throughout the page.

The Method for Making a Concave Mirror

Where the Primary Surface is on the Exterior

This alternative method creates a mold: a "forma" or template used to shape the glass or metal as wide as the span between the ends of these wooden arms. It is significantly faster than the method described above for producing a single mirror.

original: "el modo de fare lo spechio concavo"

[Diagram of a mirror-grinding machine with a rotating disk, a sturdy wooden frame, and a template used to guide the abrasive process.]

The diagram depicts a mechanical apparatus for shaping parabolic: a specific U-shaped curve that focuses light to a single point or concave surfaces. The machine uses a template—marked here with the letters S and T—to ensure the grinding tool follows a precise mathematical curve as it rotates.

S T

Various secondary sketches show mechanical components including wheels, gears, and alternative orientations for the grinding mechanism. These details illustrate how the circular motion of the crank is converted into the precise sweep required for optical polishing.

Leonardo’s use of mirror-writing (script written from right to left) is particularly evident in these technical annotations. This method, combined with his "exploded view" drawings, allowed him to visualize the internal workings of the lathe: a machine tool used for shaping materials by rotation components used in this optical workshop.

[Detailed schematic of a mechanical cart or carriage with a large central horizontal gear.]

The base of the device consists of a mobile carriage, possibly designed to allow the craftsman to adjust the pressure of the abrasive against the glass surface with high precision. By using gears: toothed wheels that transmit power, the machine can maintain a constant speed, which is essential for achieving a smooth, reflective finish without distortions.