Rembrandt usaba harina de trigo para sus pinturas/Rembrandt used wheat flour in his paintings

Un reciente estudio sobre uno de los cuadros más famosos de Rembrandt, el Retrato de Nicolaes van Bambeeck ha demostrado que entre su paleta de rojos y ocres, Rembrandt usó almidón de trigo para hacer que sus pinturas fueran, entre otras propiedades, más adherentes y transparentes. Los manuales antiguos de pintura describen el uso de almidón de trigo o de harina como una capa base que se pone sobre el lienzo o el papel, pero el nuevo estudio, publicado en la revista Analytical Chemistry por Jana Sanyova y sus colaboradores, es el primero en revelar el uso de trigo antes del siglo diecinueve, como agente modificador de las propiedades de la pintura.
En este estudio, se tomaron micromuestras de la pintura que fueron embebidas en una resina sintética que se polio hasta obtener una sección transversal plana. Estas secciones permiten no solo estudiar la estructura de las capas sino también caracterizar los componentes de cada una de ellas, empleando técnicas como la espectrometría de masas de tiempo de vuelo de ion secundario (TOF-SIMS), que es la empleada en la publicación de Sanyova. Las muestras se tomaron en 2006 durante un trabajo de restauración y han demostrado que el retrato de Nicolaes van Bambeeck está pintado sobre una base doble gris sobre roja. La primera base contiene pigmentos de tierras marrón-rojizas aplicados con una espátula de imprimación. La segunda base, gris clara y formada y basada en aceite de linaza, contiene ‘plomo blanco’ y partículas ovales grandes y pequeñas de almidón. Por encima de estas capas base, la capa de pintura al oleo está compuesta principalmente por carbonato cálcico, aluminosilicatos y partículas grandes de pigmento de negro de huesos, y laca roja compuesta de aluminio y sustratos conteniendo proteínas. También se lencuentran carboxilatos de plomo localizados en la zona de contacto con la segunda base. Es probable que se usara cola animal para sellar el lienzo.
La técnica parece muy prometedora para estudiar materials complejos biológicos o muestras arqueológicas hechas de materiales híbridos con compuestos minerales y orgánicos, y podría ayudar a entender su organización espacial supramolecular y su evolución sin poner en riesgo su integridad.

A recent study of one of the more famous Rembrandt paintings, the Portrait of Nicolaes van Bambeeck (Royal Museums of Fine Arts of Belgium, Brussels) has shown that amidst his palette of reds and browns, Rembrandt used wheat starch to make his paints stickier and more transparent, among other properties. Ancient painting manuals described the use of wheat starch or flour as a base layer of support on the canvas or paper. But the new study, published in the journal Analytical Chemistry by Jana Sanyova and col. is the first to reveal the use of wheat before the 19th century as an agent for changing the working properties of paint.
In the study, microsamples taken from the picture are embedded in a synthetic resin and polished to a flat cross-section. These cross-sections allow not only the study of the layer structure but also the characterization of the components of each layer by means of different analytical instrumental techniques such as time-of-flight secondary ion mass spectrometry (TOF-SIMS), that is the one used in the Sayova's paper. The samples were taken in 2006 during a restoration work and shown that the portrait of Nicolaes van Bambeeck is painted on a grey-on-red double ground. The first ground contains red brown earth pigments applied with a 'primer's knife'. The second ground, light grey and linseed oil-based, contains lead white and large and small oval particles of starch. Above these ground layers, the oil paint layer is composed mainly of calcium carbonate, aluminosilicates, and large particles of black bone pigment, and the red lake which is composed of aluminum- and protein-containing substrates. Some lead carboxylates are localized in this paint layer on the border with the second ground layer. Animal glue was likely used for the sizing of the canvas.
The technique seems to be a very promising tool to study complex biological or archaeological samples made from hybrid materials containing both mineral and organic compounds, and may help to understand their supramolecular spatial organization and evolution without putting their integrity at risk

Resumen de la publicación/Abstract of the paper
Unexpected Materials in a Rembrandt Painting Characterized by High Spatial Resolution Cluster-TOF-SIMS Imaging
Jana Sanyova, Sophie Cersoy, Pascale Richardin, Olivier Laprévote, Philippe Walter and Alain Brunelle
Analytical Chemistry (2011) 83, 753–760
dx.doi.org/10.1021/ac1017748

ABSTRACT: The painting materials of the Portrait of Nicolaes van Bambeeck (Royal Museums of Fine Arts of Belgium, Brussels, inv. 155) painted by Rembrandt van Rijn in 1641 has been studied using high resolution cluster-TOF-SIMS imaging. In the first step, a moderate spatial resolution (2 μm) was used to characterize the layer structure and the chemical composition of each layer on account of a high mass resolution. Then, in the second step, and despite a low mass resolution, the cluster primary ion beam was focused well below 1 μm in order to reveal smaller structures in the painting sample. The study confirmed the presence of starch in the second ground layer, which is quite surprising and, at least for Rembrandt paintings, has never been reported before. TOF-SIMS also indicated the presence of proteins, which, added to the size and shape of lake particles, suggests that it was manufactured from shearings (waste of textile manufacturing) of dyed wool, used as the source of the dyestuff. The analyses have also shown various lead carboxylates, being the products of the interaction between lead white and the oil of the binding medium. These findings considerably contribute to the understanding of Rembrandt’s studio practice and thus demonstrate the importance and potential of cluster-TOF-SIMS imaging in the characterization on a submicrometer scale of artist painting materials.