In the hushed silence of the Biblioteca Nacional de España, among the yellowed pages of Codex Madrid II, a brief annotation has waited more than half a millennium to be understood in its astonishing prophetic significance. The hand is that of Leonardo da Vinci, the universal genius whose mirror‑writing seems to shield his deepest intuitions from the superficiality of time. On folio 87r, between calculations of fortifications and hydraulic sketches, Leonardo writes with surgical precision:
“They will be better preserved if they are debarked and burned on the surface than in any other way.”
This seemingly simple phrase is not merely a technical workshop instruction; it is the manifesto of an ontological vision of matter which, today—amid environmental crisis and the search for regenerative construction solutions—emerges as the cornerstone of a new international bioarchitecture. The rediscovery of this fragment is the result of rigorous interdisciplinary research conducted by Annalisa Di Maria, internationally renowned expert on Leonardo da Vinci and Renaissance artists; Andrea da Montefeltro, molecular biologist and sculptor; and Lucica Bianchi, art historian and documentary researcher, all members of the UNESCO Club of Florence. Their study goes beyond philological recovery: it establishes a direct connection between Renaissance empiricism and the most advanced material technologies of 2025.
Leonardo did not regard wood as an inert resource to be exploited, but as a dynamic organism endowed with an “inner life” that the architect has the duty to understand and respect. Treating wood with fire, in Leonardo’s view, is not an act of destruction but a thermodynamic stabilization process capable of transforming biological vulnerability into an incorruptible armor. The urgency of this paradigm is evident today. The global construction industry—responsible for a massive share of CO₂ emissions—is desperately seeking to abandon the toxic chemical treatments introduced in the last century: preservatives that ensured immediate results at the cost of devastating environmental impact and complex disposal issues. Leonardo’s solution, grounded in the observation of natural cycles and the wise use of elemental forces, stands as the ideal antidote to the “forced chemistry” of the industrial era. This research demonstrates that European Renaissance culture had already codified a technology that the world is now rediscovering under exotic names, revealing that sustainability is not a recent invention but a long‑standing practice rooted in the wisdom of the masters.
Codex Madrid II is one of the most intimate and technical testimonies of Leonardo’s production. Written between 1491 and 1505, during the fertile Milanese period and the subsequent Florentine years, the manuscript is a laboratory of ideas in perpetual evolution. Unlike Codex Madrid I, which focuses almost uniformly on pure mechanics and gear theory, the second volume is a miscellany reflecting Leonardo’s systemic approach: every discipline is interconnected, and understanding nature is the prerequisite for every engineering success. The history of the codex itself is adventurous. Bequeathed to his loyal pupil Francesco Melzi, the manuscript passed through the hands of sculptor Pompeo Leoni and Juan de Espina before arriving at the Royal Library of Madrid, where it remained unknown for 252 years until its sensational rediscovery in 1965 by Professor Jules Piccus. This long oblivion preserved the annotations intact, written in iron‑gall ink and, in many sections, in red chalk—an iron‑oxide pigment Leonardo favored for its ability to render volume and warmth. The analysis of folio 87r reveals that Leonardo inserted the note on burned wood within a context of studies on fortifications and war machines. For Leonardo, the durability of wood was not an aesthetic detail but a strategic necessity: foundation piles, mill gears and defensive structures had to withstand decades of humidity, fungi and insects under extreme environmental conditions. His prescription—removing the bark and carbonizing the surface—responds to a logic of active protection that transforms the material’s outer layer into an inert, hydrophobic barrier. The answer lies in the complex chemistry of pyrolysis, the thermal decomposition of wood in low‑oxygen conditions.
Although Leonardo lacked the vocabulary of modern organic chemistry, he perfectly understood the physical consequences of controlled fire exposure. His instruction to “burn on the surface” aims to create a layer of amorphous carbon that acts as a thermodynamic shield for the structural core of the beam.
A detailed table of thermal decomposition stages follows (translated faithfully), along with the three critical factors identified by Di Maria, Montefeltro and Bianchi:
1. Removal of Bark – eliminating moisture traps and insect habitats.
2. Elimination of Nutrients – fire consumes sugars and hemicellulose, depriving fungi of sustenance.
3. Hydrophobic Carbon Layer – heat seals pores and crystallizes resins, creating a waterproof barrier.
Paradoxically, this treatment also increases fire resistance: carbon has low thermal conductivity, slowing heat propagation during a fire and preserving structural integrity far longer than untreated or chemically coated wood.
A table follows (translated), showing Leonardo’s identification of mechanical properties and suggested uses for oak, chestnut, ash, linden, alder, willow, maple and poplar
As Annalisa Di Maria highlights, Leonardo applied mathematical proportions and the golden ratio not only to portraits and anatomical studies but also to the understanding of natural structures. Wood, with its oriented fibers and growth rings, was for him the visible manifestation of a divine geometry applied to constructive matter. One of the most striking findings of the study is the parallel between Leonardo’s note and the Japanese Yakisugi (Shō Sugi Ban) technique. Although the two cultures had no direct contact in the 15th century, they arrived at the same technological solution for the universal challenge of wood durability. Leonardo’s note predates the earliest written Japanese documentation by more than a century, demonstrating a case of convergent invention.
Today, Leonardo’s intuition is shaping some of the world’s most ambitious architectural projects. In an era demanding low‑emission buildings and carbon‑sequestering materials, charred wood has emerged as the ideal solution for façades and structural elements. The most emblematic example is the new Doris Duke Theatre at Jacob’s Pillow (Massachusetts), designed by Mecanoo and inaugurated in July 2025. After the devastating 2020 fire, the theatre was rebuilt entirely with charred wood cladding—seven horizontal bands symbolizing the indigenous “seven generations” principle. The interior, described as a “magical wooden box,” offers a complete sensory experience. Studies presented in 2025 confirm that natural materials such as fire‑treated wood reduce cortisol levels and improve perceived air quality. Leonardo, who considered art a “cure for the soul,” would have appreciated how his constructive technique now contributes to human well‑being.
The Team of Experts
In a world governed by strict environmental regulations—such as France’s 2022 law requiring 50% wood in public buildings—Leonardo’s technique offers a master path toward decarbonization. The research by Di Maria, Montefeltro and Bianchi reveals a Leonardo who is far more than a painter or inventor: he is the precursor of a culture of material care. His note in Codex Madrid II teaches that innovation does not necessarily lie in inventing new synthetic molecules, but in rediscovering nature’s latent potential through observation and experiment. To build today means returning to that “fire that preserves life” of which Leonardo wrote within the walls of Sforza‑era Milan. It is in the balance between the hand of the craftsman, the eye of the scientist and the soul of the material that contemporary bioarchitecture finds its most authentic root and its brightest promise. Leonardo, who saw wood as a breathing body, reminds us that sustainability is not a technical choice but an ethical imperative: the duty to design for the “seven generations” to come, with the same care he devoted to his models and masterpieces.
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