The Department of Painting of the EHU-University of the Basque Country has come up with a multi-analytical methodology to identify the white haze appearing on oil paintings

Researchers in the EHU’s FARMARTEM group used this methodology to determine the origin of the degradation problems of the oil painting Izenik gabe by the Basque artist Santos Iñurrieta: metal soaps are responsible for the white hazes. This research constitutes a huge step forward in the long-term conservation of contemporary art, since it gives a detailed view of the validity of all the techniques used and the specific information provided by each one.

Changes in oil paintings can occur due to interactions between their chemical components and external factors, including the formation of off-white substances all over the painting or on specific sections. But these white hazes do not always have the same appearance and their origin may also be different. “These substances that whiten the surface of works of art not only affect the aesthetic side, they are also a conservation issue and it is very important to know the causes so that we can address the problem,” explained Erika Tarilonte, researcher at the EHU’s Faculty of Fine Arts.

The work Izenik gabe by the Basque artist Santos Iñurrieta (1950-2023) is in unvarnished oil paint on canvas and a homogeneous, brittle off-white substance covers much of the painting. Researchers in the EHU’s FARMARTEM group focussed on this painting to carry out the most complete analytical study to date to identify the phenomena of surface whitening of contemporary oil paintings. “We specified a comprehensive multi-analytical methodology that will be useful in analysing certain degradation phenomena and conserving paintings,” explained Tarilonte. This research is a great step forward in addressing one of the biggest problems in the conservation of contemporary art today.

First and foremost, the historical-artistic study of Iñurrieta’s works of art showed that these white hazes had not been intentional, and, on the basis of that, the researchers examined various hypotheses. “Fungi, or salt crystallization, migration of fatty acid, the oozing of wax, metal soaps, etc. could be responsible. The analyses we carried out revealed that lead soaps are the main cause of the white hazes on the painting and that the source of the lead was most likely a lead-based drying agent,” said the EHU lecturer. The process in which lead soaps form takes place within the paint layer, “but little by little, over time, they emerge and a white haze appears. It looks as if the artwork has been misted over”.

Vital information to effectively eliminate the hazing phenomenon

The research also made available extensive information about the materials and techniques used by the artist in the painting. “We now know about the paint layers in the work of art: what they are like; their thickness; their grain size; precisely which pigments were used, which additives, which binders, etc. Following this research, we know everything about the work of art, and today this is very important to be able to intervene subsequently.” The EHU researchers said this was the first step: “This is what the work of art is like now, but we know that the original was not like this. The next obvious step would be to intervene in the work of art, clean it up and leave it as it was originally.”

So the researchers in the FARMARTEM group proposed a multi-analytical study to detect the origin of white hazes in oil paintings: a range of microbiological studies, X-rays, fluorescence studies, chemical, microscopic, spectroscopic analysis of microsamples, computerized tomography, chromatography scans, etc. The EHU researchers have made available to the scientific and artistic community detailed information on the usefulness of all these techniques and the specific information provided by each one.

Indeed, “thanks to the flexibility of this multi-analytical methodology, we found that some techniques that do not provide significant results for metal soaps can nevertheless provide useful information about other hazing phenomena”, said Tarilonte. For example, she has now turned her attention to another work of art: Alberto Gonzalez’s Izenik gabe (1978). “This work of art has white hazes, but the morphology of the haze, its appearance, is different: it has white dots on a specific blue colour,” she explained. One of the main hypotheses of the researchers is that “salt crystallization is responsible for these accretions. The methodology we have developed will only enable us to use the most interesting analytical techniques to study salt crystallization, not all of them. Now we know what kind of information each technique can give us, so when investigating other works of art, we will select only the most useful ones on the basis of each case. We have provided an opportunity of adapting according to each case”.

Despite significant progress in this area, “much research is still needed on the causes and mechanisms that cause the hazing. This work will serve to develop better strategies for conserving oil paintings and for investigating effective remedies for the long-term conservation of works of art”, explained the EHU researcher.

Additional information

This research is part of the PhD thesis by the EHU lecturer Erika Tarilonte-Perez. Her thesis supervisors are Oskar González-Mendia and Miren Itxaso Maguregui-Olabarria, researchers and lecturers at the EHU’s Faculty of Fine Arts. The research was conducted in collaboration with the IBeA and Fungal and Bacterial Biomics research groups with the assistance of the SGIker service. In the first section of her thesis, Tarilonte worked on and set up a preventive conservation plan for the Orbegozo Foundation’s collection of paintings. Currently, the researcher is involved in the restoration of the works of art in this collection.

The Orbegozo Foundation houses one of the most important private collections of contemporary art in the Basque Country; it includes more than 350 works by important Basque and Spanish artists, such as Zumeta, Ortiz de Elgea, Santos Iñurrieta, José Barceló, Juan Mieg, Gallo Bidegain and Díez Álava.

Bibliographic reference

Erika Tarilonte, Oskar González-Mendia, Ilaria Costantini, Kepa Castro, Itxaso Maguregui

A multi-analytical approach for the identification of surface whitening phenomena in contemporary oil painting and its application to metal soaps

Journal of Cultural Heritage

DOI: 10.1016/j.culher.2025.06.007