{"id":18264,"date":"2020-01-23T12:52:49","date_gmt":"2020-01-23T13:05:00","guid":{"rendered":"https:\/\/blog.museunacional.cat\/?p=18264"},"modified":"2020-06-19T10:03:31","modified_gmt":"2020-06-19T10:03:31","slug":"the-periodic-table-through-the-rooms-of-the-museum-ii","status":"publish","type":"post","link":"https:\/\/blog.museunacional.cat\/en\/the-periodic-table-through-the-rooms-of-the-museum-ii\/","title":{"rendered":"The periodic table through the rooms of the museum II"},"content":{"rendered":"\n

N\u00faria Oriols<\/strong><\/p>\n\n\n\n

\"Identification<\/a>
Identification of chrom yellow and tin in a stratigraphy from the work by Annibale Carracci, Apostles around the Empty Sepulchre<\/a><\/em>, 1604-1605.<\/figcaption><\/figure>\n\n\n\n

We continue our visit to the museum\u2019s rooms\nthat we began in last\nweek\u2019s article<\/a>.<\/p>\n\n\n\n

Renaissance and Baroque art rooms <\/h3>\n\n\n\n

Preparations with clays <\/h4>\n\n\n\n

As we move into a new room, we observe another change in the type of format. In the different sections of this period the majority of paintings are on canvas. In the palaces of the period, with walls filled with works of art, it was necessary to find a way of reducing the weight of the paintings. <\/strong>Replacing wooden supports with canvas ones was the first step in this direction. Nevertheless, the plaster traditionally used for the preparatory layer was still too dense. For this reason, the different workshops of schools and painters, located in particular geographical areas, began investigating and trying out new, lighter materials, using above all clays<\/a> or earth from the surrounding area. This practice means that the chemical composition of preparations in this period has become a sort of identity code related to the provenance of the works.<\/strong> A preparation from Seville is nothing like one from Madrid, for example, in terms of composition and colour.<\/p>\n\n\n\n

As aluminosilicates<\/a>, clays contain an important proportion of silicon and aluminium, elements present in abundance, therefore, in the preparations of the canvases painted by Ribera<\/a>, Vel\u00e1zquez<\/a>, Ribalta<\/a>, Van der Hamen<\/a>, Ma\u00edno<\/a> and Goya<\/a>, among others. In the preparations one also detects minor elements such as calcium, potassium or iron, the latter responsible for the characteristic reddish colour of Baroque preparations. If manganese (Mn)<\/a> is present in it, as has been detected in the preparatory layer of the work Still life with basket of plums and melon piece<\/a><\/em>, by Zurbar\u00e1n,<\/a> then the colour of the clays is almost black. But let\u2019s get back to the colours.<\/p>\n\n\n\n

\"Francisco<\/a>
Circle of Francisco de Zurbar\u00e1n, <\/a>Still life with basket of plums and melon piece<\/a><\/em>, 1640-1650.<\/a><\/figcaption><\/figure>\n\n\n\n

From ultramarine to cobalt blue <\/h4>\n\n\n\n

We normally\nassociate the name <\/strong>cobalt (Co)<\/a> with blue. <\/strong>Cobalt\nblue as used by contemporary artists dates back to the late seventeenth century<\/strong>,\nwhen Jean Antoine Chaptal, a minister \u2013 and chemist \u2212 in the French government,\nasked Louis\nJacques Th\u00e9nard<\/a> and Jean-Fran\u00e7ois\nL\u00e9onor Merim\u00e9e<\/a> to do research in order to improve\nthe pigments in use up to then. From what he had observed in the manufacturing\nof porcelain in S\u00e8vres, Th\u00e9nard experimented with mixtures of cobalt arsenate, cobalt\nphosphate and aluminium oxide, heating them until he managed to obtain a new\npigment, which\nwas called cobalt blue<\/strong>. He\npublished these results in the Journal\ndes mines <\/em>in 1803-1804, with the title \u00abSur les couleurs, suivies d\u2019un proc\u00e9d\u00e9 pour\npr\u00e9parer une couleur bleue aussi belle que l\u2019outremer\u00bb<\/em><\/a>. Throughout\nthe entire history of art the blue of the semi-precious stone lapis lazuli has\nbeen especially appreciated; it was also called ultramarine, because the Italians\nimported it from overseas, from mines in what is now\nAfghanistan. Cobalt blue, however, did not manage to\nreplace it completely, because years later, also in France, the Soci\u00e9t\u00e9\nd\u2019Encouragement pour l\u2019Industrie Nationale offered a prize of 6,000 francs to\nwhoever could come up with a way of manufacturing artificial ultramarine blue that\ndid not exceed 300 francs per kilogramme. Jean Baptiste Guimet<\/a>\nwon the competition on 4 February 1828, and from then on the high cost of lapis\nlazuli ceased to be an impediment for obtaining its characteristic colour.<\/p>\n\n\n\n

Throughout the history of art, blue has always been a particular\ncolour, appreciated, but hard to obtain, due to the scant availability of\nnatural substances that present it permanently.<\/strong> Although\nscarce in nature, cobalt is contained in some minerals. Cobalt oxide has been incorporated\ninto the manufacture of materials at different times in the history of ancient\nand modern civilizations, giving glass, enamels and ceramics a deep blue colour.\nIn this context, it is easy to understand why the step was taken from crushing\nblue glass in order to use the powder obtained to paint with. This is the case\nwith the pigment known as blue enamel,<\/strong>\na potassium glass that contains cobalt, used particularly in painting from the\nsixteenth to the eighteenth century.<\/p>\n\n\n\n

El blau esmalt<\/h4>\n\n\n\n

Annibale Carracci<\/a> (1560-1609) used blue enamel in the skies of the mural paintings in the The Herrera Chapel. Church of San Giacomo degli Spagnoli<\/a> <\/em>in Rome, commissioned in 1602 by Juan Enr\u00edquez de Herrera, and which can now be seen in room 36. We also find it in the sky in the work The Conversion of Saint Paul<\/a><\/em> painted by Juan Bautista Ma\u00edno (1581-1649), but on this occasion its presence is not obvious. It is applied in a base layer, underneath the azurite, a pigment far more appreciated and expensive. It has also been identified in the layers underlying the blue azurite in the work King Wenceslaus IV Sentences Saint John of Nepomuk<\/a><\/em> by Paolo de Matteis (1662-1728). During the restoration of this work, some fissures appearing only in the areas painted dark blue were observed, which must have been caused by the presence of blue enamel. Potassium glass is chemically less stable than sodium glass. When blue enamel is mixed with an agglutinant such as linseed oil, the fatty acids this contains are able to react with the potassium in the glass and form salts, potassium soaps. This chemical reactivity, on a microscopic scale, eventually brings about, at a macroscopic level, a change in the texture of the agglutinant, causing breakages that explain the fissures. At the same time, the absence of potassium in the structure of the glass determines that this is also affected and it becomes totally transparent. Therefore, blue enamel is a pigment with a rather unstable colour that tends to turn grey or even become clear.<\/strong> Some of the colours now present in paintings by El Greco<\/a>, for example, can be explained by the alteration of this pigment. And in the polychrome sculpture Wilgefortis<\/a> <\/em>of 1689, recently restored and exhibited, at the same time as the bearded figure was identified with a Saint Liberata, it was discovered that its clothes, now a vague brownish colour, must originally have been blue: its polychromy is full of the elements silicon, potassium and cobalt.<\/p>\n\n\n\n

\"Estratigrafies<\/a>
Stratigraphies of micro-samples that contain the pigment blue enamel. On the left, the sample comes from the sky in the work Apostles Around the Empty Sepulchre<\/a><\/em> by Carracci, 1604-1605. On the right, the sample comes from the work Penitent Magdalene<\/a><\/em> by El Greco, c.<\/em> 1590 (Museu del Cau Ferrat, Museus de Sitges).<\/figcaption><\/figure>\n\n\n\n
\"Annibale<\/a><\/figure>
\"Paolo<\/a><\/figure><\/div>
\"Juan<\/a><\/figure>
\"Andreu<\/a><\/figure><\/div><\/div><\/div><\/div>\n\n\n\n