Looking for Novel Natural Gels to Improve Cleaning Methods for Bronze Leachates on Marble

Marble is one of the materials most susceptible to copper leaching, resulting in easily identifiable turquoise stains on the marble. This problem is particularly relevant when we are talking about marble structures of heritage value. For this reason, conservators look for cleaning materials that are specific to the structure to be treated without damaging the original surface. Materials such as agar have been studied for a long time. Agar creates a controlled water release system that adapts to the needs of conservators who seek the greatest possible cleanliness without damaging the material to be treated. To improve the cleaning, chelating agents such as EDTA are added to the agar composition. However, the microbiological growth and the damage it produces to the original material are disadvantages to take into account. In order to solve these problems, other natural materials with cleaning potential such as kudzu and konjac gels were studied in combination with other chelating agents such as citrate, oxalate, and gluconic acid. For the characterization and evaluation of copper cleaning, various analytical techniques were used, including Raman spectroscopy, colorimetry, X-ray fluorescence (XRF), and inductively coupled plasma mass spectrometry (ICP-MS). In this study, both konjac and kudzu emerged as promising alternatives to agar, revealing distinctive features such as simplified preparation methods and inherent antimicrobial properties. The EDTA chelator was found to be the most harmful for marble surfaces, as it extracted a greater amount of calcium from the marble during application of the gels doped with it. Citrate and gluconic acid have been identified as a promising substitute to prepare doped gels for the removal of copper stains. These compounds exhibit comparable or potentially superior cleaning capabilities than EDTA, with no negative side effects.This work has been supported by the project DEMORA (Grant PID2020-113391GB-I00) funded by MCIN/AEI/10.13039/501100011033 and by “ERDF A way of making Europe” (EU)

Estudio de la viabilidad de la limpieza de manchas metálicas generadas por lixiviados de bronce sobre mármol utilizando geles naturales

[ES] El patrimonio cultural es un ámbito que requiere un buen cuidado de sus bienes. Tanto su conservación como restauración deben hacerse de la forma menos invasiva posible, a fin de no estropear las obras de arte. Pero esta tarea no siempre es fácil. En lo que implica la aparición de manchas de lixiviados de cobre en superficies de mármol, una de las alternativas más novedosas para su limpieza es el uso de geles semirrígidos de Agar. Estos geles, gracias a su adhesividad y poder de absorción, permiten la extracción de los metales sin provocar daños en la superficie. Por ello, es un campo de interés, en el cual se encuentran opciones similares como el Kudzu y el Konjac. Además, el añadir quelantes a estos geles, puede incrementar su capacidad de extracción. Este trabajo comprueba la efectividad en la limpieza de lixiviados de cobre con geles semirrígidos de Agar, Kudzu y Konjac, realizándose dos aplicaciones de 8-h cada una. Los aditivos que presentaron mejores extracciones fueron el citrato sódico, EDTA y ácido glucónico. Se utilizaron técnicas como colorimetría, XRF y espectroscopía Raman para la caracterización de las probetas de mármol, así como ICP-MS para analizar el contenido de los diferentes geles.[ENG] Cultural heritage is an area that requires good care of its assets. Both its conservation and restoration must be done in the least invasive possible way, so as not to damage the artworks. But this task is not always easy. In what involves the appearance of copper leachate stains on marble surfaces, one of the newest alternatives for their cleaning is the use of semi-rigid Agar gels. These gels, due to their adhesiveness and absorption power, allow the extraction of metals without causing damage to the surface. This is therefore a field of interest, in which similar options such as Kudzu and Konjac are found. Moreover, the addition of chelating agents to these gels can increase their extraction capacity. This labwork tests the effectiveness in the cleaning of copper leachates with semi--rigid Agar, Kudzu and Konjac gels, with two applications of 8 h each. The chelating agents that showed the best extractions were sodium citrate, EDTA and gluconic acid. Techniques such as colorimetry, XRF and Raman spectroscopy were used to characterize the marble mock-ups, as well as ICP-MS to analyze the content of the different gels