Recognizing the heritage behind Hugo Díaz’s caricature for the Costa Rican children’s novel Cocorí using non-destructive techniques

Artworks are not just images; they are physical objects made of materials that age, change, and sometimes break down. A painting on canvas or a drawing on paper exists in a delicate balance between the artist's intent and the environment it inhabits. Over time, light, humidity, and even the touch of human hands can alter these materials, causing colors to fade, paper to become brittle, or microscopic life to take hold. Preserving these works requires understanding exactly what they are made of and how they are changing, but traditional methods of investigation often involve taking samples or using harsh chemicals that can damage the very object being studied. This is where non-destructive techniques come in, offering a way to look inside an artwork's history without ever touching its surface with a blade or a solvent. By using light, sound, and gentle scanning methods, scientists can map the condition of a piece, identify the pigments an artist used, and detect the presence of invisible threats like bacteria or fungi, ensuring that these cultural treasures survive for future generations to see.

In Costa Rica, a team of researchers turned their attention to a specific piece of national heritage: the original cover illustration for the beloved children's novel Cocorí. Created in 1995 by the renowned Costa Rican cartoonist and illustrator Hugo Díaz, the artwork depicts the story of a young boy's journey through a tropical jungle. While the book has been a staple of education for decades, the original watercolor and ink drawing had never been subjected to a deep scientific examination. The team, comprising experts in physics, microbiology, and art history from the University of Costa Rica, set out to understand the drawing's current state of health using only non-invasive tools. Their goal was not to restore the image, but to create a detailed map of its condition, identifying exactly where it was most vulnerable to damage and what materials were at risk.

The researchers began by treating the artwork like a landscape to be surveyed. They photographed the drawing using different types of light, including visible light, infrared, and ultraviolet. Visible light showed the bright, uniform colors Díaz had applied, while infrared light penetrated the top layers of paint to reveal the artist's original pencil sketches hidden underneath. This allowed the team to see where Díaz had changed his mind or adjusted the lines before finalizing the image. Ultraviolet light, meanwhile, acted as a spotlight for repairs, causing areas where someone had previously tried to fix a mistake to glow differently than the original surface. By combining these views, the team built a comprehensive picture of the drawing's history, from the artist's first strokes to later interventions.

To understand where the paper itself was weakest, the team developed a system called Priority Attention Zones. They divided the drawing into a grid of one hundred squares and examined each one for signs of wear, such as wrinkles, water stains, or brown spots known as foxing. They assigned a severity score to each square based on the type and amount of damage found. When these scores were plotted on a map, a clear pattern emerged: the edges of the drawing were in the most critical condition. This makes sense, as the corners and borders are the parts most likely to be touched by human hands or exposed to fluctuating humidity. The map revealed that these outer zones were not just physically worn but were also the most likely places for biological growth to occur, effectively highlighting the areas that needed the most urgent protection.

The scientists then looked closely at the paper's structure to see how the damage affected its density. By measuring the size of the tiny fibers that make up the paper under a microscope, they could estimate the weight of the paper in different areas. They found that in places where the paper was wrinkled or had runny pigment, the material had effectively lost mass or expanded, making it thinner and weaker. Conversely, in areas with oxidation stains, the paper seemed to have gained mass or become compressed, suggesting it had absorbed something from the environment. This detailed analysis allowed them to quantify exactly how much the paper's structure had changed in response to different types of damage, providing a scientific basis for how to handle and store the piece in the future.

To identify the colors Díaz used, the team employed a technique that bounces light off the surface of the painting and measures how the light behaves. This method, known as fiber optics reflectance spectroscopy, acts like a fingerprint scanner for pigments. By comparing the light patterns from the drawing to a database of known colors, they confirmed that the artist used a specific palette including Burnt Sienna or Umber for the earth tones, Ultramarine Blue for the sky and water, and Naples Yellow or Raw Sienna for the lighter, cream-colored areas. The analysis also showed that some of the blue areas had been altered by biological activity, as the light patterns in those spots were distorted, indicating that something living had grown there and changed the chemical makeup of the paint.

The most direct evidence of this biological activity came from the team's work with microorganisms. They gently swabbed four specific spots on the drawing where brown stains were visible and grew the samples in a laboratory. They discovered two distinct types of life that had colonized the paper. One was a bacterium called Staphylococcus epidermidis, which is commonly found on human skin. Its presence suggests that the artwork has been handled frequently without gloves, likely during the printing process or while being moved over the years. The other organism was a fungus called Rigidoporus microporus, a type of wood-rotting fungus often found in the tropical forests of Costa Rica. This fungus is particularly concerning because it produces enzymes that can break down the cellulose in the paper, essentially digesting the drawing from the inside out.

The study concluded that while the drawing is a small-scale piece originally intended for reproduction rather than long-term preservation, it has become a vital piece of Costa Rican cultural identity. The research provided a clear, evidence-based roadmap for its care. The Priority Attention Zones map showed exactly where the paper is most fragile, the pigment analysis confirmed the materials used, and the microbial identification revealed the specific threats posed by human handling and environmental fungi. By understanding these factors, curators can now control the temperature and humidity in the storage environment to stop the fungus from growing and ensure that the vibrant image of Cocorí remains intact. The work demonstrates that even for a piece of art not originally meant to last forever, modern science can offer the tools to protect its legacy, allowing future generations to see the world through the eyes of Hugo Díaz.