Adorning the walls of San Ildefonso College in Mexico City is artist Diego Rivera's masterpiece, rendered in fresco and gold leaf, The Creation, or La Creacioń. It depicts a man standing with his arms outstretched beneath a deep blue celestial disk studded with stars and constellations, while figures seated on clouds watch from either side. The work catalyzed the revival of the encaustic painting technique in the 1920s.

In a recent study published in ACS Omega, researchers from Mexico set out to identify the specific materials Rivera used for the mural La Creación.

Encaustic paint is traditionally made by melting pigments into a blend of beeswax and resins. Rivera claimed his Mexican version was different, as his formula involved mixing copal and beeswax with other ingredients, then torching the surface to fuse them in place. To test that claim, researchers conducted a detailed chemical analysis of tiny samples taken from the mural, comparing them with mock-ups made using Rivera's own recipe.

The chemical fingerprint of the mural told a different story from what Rivera claimed. The biggest surprise was the absence of beeswax; not a trace of it showed up in any mural sample, even though Rivera insisted his mix was half wax.

The mural's primary binder turned out to be copal resin rather than beeswax. Despite the missing wax, the work still qualifies as encaustic, since the label depends on how the paint was applied, using heat, not on what it's made of.

What's hiding in the paint?

Mexican muralist Rivera painted his first mural, Creation, between 1922 and 1923 at the Amphitheater of the National Preparatory School, now known as the Antiguo Colegio de San Ildefonso (San Ildefonso College). During an interview while he was working on the mural and even years later, Rivera claimed he used encaustic, a wax-based painting technique, with copal resin added to create a distinctly Mexican recipe.

Copal is a fresh resin that oozes from Bursera trees. While 18th-century Europeans struggled with the tougher varieties they encountered, fresh Mexican copal melts with ease, carries a sweet aroma and dissolves readily, making it far easier to work with.

Rivera's technique caught on fast as artists across Mexico and South America soon followed his lead, adopting similar encaustic methods for their own murals. His formula came together in two parts, one made of beeswax blended with lavender oil, the other a mix of copal resin, elemi resin, and solvents, all heated together with paint pigments in a double boiler.

However, no one had ever scientifically tested whether the paintings actually contain what's written in the recipe. This information is crucial for conservation, since cleaning or restoring the mural with the wrong methods could permanently damage it, and experts need to know its exact composition to do the work safely.

Before testing the actual masterpiece, researchers built their own paint samples, called mock-ups, following Rivera's documented recipe, then applied them to cement blocks meant to mimic the mural's original wall.

To replicate Rivera's technique, they heated the practice samples with a blowtorch for 15 seconds, just as he would have. This let them track exactly how the paint's chemistry shifted under intense heat, creating a chemical profile they could then compare against the real mural.

The team then took tiny samples (1–2 milligrams each) from different locations on the actual mural, La Creación. They put both the practice samples and the real mural samples through mass spectrometry, high-resolution microscopy, and nuclear magnetic resonance, among other high-tech analyses, to extract the chemical fingerprints of the specific ingredients.

The analysis turned up no traces of beeswax in the mural samples. Researchers first suspected heat might be to blame, so they ran mock-up experiments to check, but wax markers held up fine even after burning, ruling that out.

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The graphs made it clear that copal resin was the primary binder, with mineral fillers such as calcite, barite, talc, and gypsum layered throughout the paint. The chemical report also flagged zinc lactate as a degradation product, likely formed when heat from Rivera's blowtorch triggered a reaction between the white pigment, zinc oxide, and the resin binder.

Ethyl phthalate turned up in every sample taken from the mural. Researchers believe it wasn't part of Rivera's original recipe but a byproduct of either exposure to air pollution or earlier conservation work.

Beyond uncovering hidden histories in iconic artworks, the study offers a chemical reference point for preserving Rivera's murals and the work of his contemporaries. Future studies could dig deeper into how these ingredients are distributed across the mural and how they interact with the heat used in encaustic painting.

Written for you by our author Sanjukta Mondal, edited by Sadie Harley, and fact-checked and reviewed by Robert Egan—this article is the result of careful human work. We rely on readers like you to keep independent science journalism alive. If this reporting matters to you, please consider a donation (especially monthly). You'll get an ad-free account as a thank-you.

Publication details

Pablo Aguilar-Rodríguez et al, An Encaustic without Wax: Microanalytical Binder Characterization of Diego Rivera's First Mural, Experimental Reproduction, and Identification of Degradation Products, ACS Omega (2026). DOI: 10.1021/acsomega.6c00983

Who's behind this story?

Sanjukta Mondal

Master's in Chemistry. Freelance science journalist and communicator. Published in Chemistry World, BioSpace, and The Hindu. Full profile →

Sadie Harley

BSc Life Sciences & Ecology. Microbiology lab background with pharmaceutical news experience in oil, gas, and renewable industries. Full profile →

Robert Egan

Bachelor's in mathematical biology, Master's in creative writing. Well-traveled with unique perspectives on science and language. Full profile →

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Citation: Diego Rivera claimed his mural Creation was half wax, but chemical forensics says otherwise (2026, July 31) retrieved 31 July 2026 from https://phys.org/news/2026-07-diego-rivera-mural-creation-wax.html

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