The author recently had the opportunity to carry out research into the technique of more than one hundred Italian works of the 17th and 18th century working in collaboration with Dr Ladislav Daniel. Most of the pictures are the property of the National Gallery in Prague, mainly works in the depositaries to which little attention had been paid. Some important pictures belong to the Gallery of Art in Olomouc and the Archbishop's Collection which is deposited there. This article is a synopsis of the results of the research, and the data found are compared with period sources.

All pictures were X-rayed, the originality of the painting was checked. The analysis of the pigments and bonding agents was carried out in collaboration with the laboratory of the National Gallery, whose findings form a separate part of this study. Special attention was devoted to the ground layers which form the optical base of Baroque painting, whose composition and tone are, to a large extent, symptomatic. These layers were studied on microscopic sections, and the individual components were analysed. The method is described in the laboratory report.

The possibility of distinguishing certain regions or periods of time on the basis of the system of ground layers is more difficult in the Baroque period than in 16th century Italian painting where the gradual development of toning imprimatura can be traced, as we have shown elsewhere. These imprimatura, whose tone gradually darkened towards the end of the century, are, in fact, forerunners of the Baroque grounds, for they meant a basic change in the optical construction of the picture by making it possible to apply lights in the first phase of painting. In tone they do not differ from Baroque grounds that contain colour pigments in the entire matter and sometimes even exceeded it in darkness. They differed, however, by always being combined with the lower gesso that disappeared only at the turn of the 16th to 17th century. There exist rare exceptions such as two of Tintorettos pictures, where a mere mixture of pigments forms the ground. The danger of the paint darkening through the influence of toned imprimatures is compensated for in the 16th century by light underpainting. A similar system was taken over into the technique of Baroque painting where a binding feature was a ground of bole earths in modifications of grey with relatively dark underpainting. In some cases this grey underpainting was replaced by a continuous medium grey layer that served a similar function, i.e. to preserve the colour intensity of the painting and provide fine transitions from light to shadow. Michelangelo Caravaggio used such a system of a dark brown ground with a grey layer above it form his cycle of pictures in the Church of San Luigi dei Francesi in Rome in the year 1602 1. Only where stress is placed on a sharp contrast of light and shadow is the paint placed directly on the dark ground, as can be seen especially in the naturalistic current of Neapolitan painting.

Francesco de Rosa, called Pececco de Rosa: St Dorothea National Gallery, Prague DO 4309, detail in x-rays. Charakterictic canvas structure - loose weave.

The expressly chiaroscuro concept of the picture of St. Jerome by Jusepe de Ribera of the year 1646 (National Gallery) is based on a dark brown ground layer made of a rough-grained heterogenic mixture and applied in a relatively thick coat. No underpainting was found. According to the X-ray such thick layers were applied with sharp brushwork straight on to the ground, whose tone shows in the general dark tonality of the picture. A similar technique can be found in the work of Francesco De Rosa, called Pacecco, three of whose paintings in Czech collections we analysed after their attribution by Dr. Ladislav Daniel: St. Anthony with the Christchild (National Gallery), St. Dorothy (National Gallery) and St. Joseph with the Christchild (Chateau at Mnichovo Hradiště). The dark brown ground is applied to a canvas of the net type as in the case of Ribera's Jerome. The structure of the canvas shows on the surface of the painting in finerectangular crackels but the paint does not rise nor are deep cracks formed as in the technique of thick ground layers applied to dense canvas. Pacecco's brushwork of thick and sharp layers as well as the absence of underpainting are features related to Ribera's technique.

The use of black imprimatura on a dark ground, which we can meet in some works of the naturalistic Neapolitan School, leads to sharp transitions from light to shadow and to an absence of semi-shades so that the painting makes a flat impression. This phenomenon is typical of marginal, second-rate work. The subdueing of the undesirable effect of dark grounds by a continuous grey layer suited painting, it seems, for which certain Neo-Classical trends are typical. We can find a twolayered ground of this type e.g. in the technique of the picture by Simone Vouet, The Suicide of Lucretia, a work whose relationship to the art of Guido Rent was shown at an exibition in the National Gallery in Prague arranged by Dr. Ladislav Daniel and called Reniana. A similar type of ground but with a black lower layer was used by Nicolas Poussin, whose influence on the painting of Giulio Carpioni can be traced also in this technical detail, as shown by the analysis of four pictures by Carpioni in the Prague National Gallery. The relatively light-grey second layer of the ground makes a more intensive colour scheme possible and gives the picture considerable luminosity.

Jusepe de Ribera: St Jerome cross-sections
from the right edge

a/ background
3 - dark mixture of brown, black and red
pigments 0,057 mm
2 - brown ground: yellow and red ochres, lead white and colourless siliceous particles 0,263-0,350 mm
1 - fibres of the canvas

b/ white leaf
3 - varnish layer 0,012 mm
2 - white painting: lead white and carbon black 0,026-0,050 mm
1 - brown ground: yellow and red ochres, lead white and colourless siliceous particles 0,386 mm


Luca Giordano:
St Sebastian white drapery from the lower right corner

3 - varnish layer 0,01 mm
2 - white painting: lead white, smalt and carbon black 0,042 mm
1 - yellow-brown ground: yellow and red ochres, lead white and colourless siliceous particles 0,350-0,440 m

Grey underpainting of varying intensity was found in the technique - a very sophisticated one - of Bernarda Cavallino. The apparently flowing painting of his Virgin Suckling the Infant Christ in the Olomouc Art Gallery is applied in layers, the lowest of which, in regard to brushwork, can be seen only on an X-ray photograph. The Neapolitan technique of dark ground layers in brown tone on a loose canvas of the net type was not limited to the naturalistic current. We can find a similarity also in the work of Massino Stanzione, as shown by his St. Catherine in the Olomouc Art Gallery. Another example is the Neo-classical picture by a Neapolitan painter c. 1650, The Archangel Michael Who Fights a Fallen Angel (National Gallery). But the brushwork of the painting is different, apparently smooth on the surface applied in thick layers. An X-ray reveals a loose stroke of the brush in the lower layer. The skilful colour scheme is proof of a different, a new style.

In Neapolitan painting of the High Baroque style of the second half of the 17th century, as represented by Lucca Giordano, a further change of brushwork took place. Typical of the loose concept are long brushstrokes that do not hide the marks of the brush. Such a concept was revealed on an X-ray picture of St. Sebastian, belonging to the National Gallery, originally attributed to Ribera. Dr. Ladislav Daniel is convinced that it is the work of Lucca Giordano. The optical base of this picture is traditional: a dark brown ground on netting. Giordano's looseness of concept and his stress on the beauty of form has, it seems, its continuation in Neapolitan painting of the first half of the 18th century when Francesco Solimena became the leading figure.

Luca Giordano: St Sebastian, National Gallery, Prague

Lot's Flight from Sodom, a picture belonging to the Prague National Gallery, which was unknown and only recently restored, is painted in soft brushwork, and its colour scale has a strikingly broad range of full tones. Dr. Ladislav Daniel is of the opinion that it is very close to Solimena. Here, too, the traditional brown ground on a netting canvas is to be found.

Naples holds an important place in our collections and therefore deserved attention was devoted to it. A numerically far smaller share belongs to Bologna, which, as is known, greatly influenced the beginnings of the Italian Baroque style. Bologna painting is likewise represented in a number of outstanding works in our country. Among these should probably be counted the small picture of the Virgin Suckling the Infant Christ by Elisabetta Sirani, dated 1663, which was fairly recently acquired for the National Gallery and then restored. The X-ray shows the loose brushwork of this young paintress, who died at an early age. The rather complex technical composition is based on an optical addition of a brown ground and two grey layers of the background with an intermediary layer of red varnish. The classical concept of painting of Elisabetta Sirani was influenced by the example of Guido Reni.

After this brief survey of some examples of Italian Baroque technique we present a summary of data of more or less statistical character as gained in the course of research into one hundred pictures. These technical data are given according to a system that traces the process in which the paintings originated.

Support: 96% canvas predominantly in plain weave, only in 4 cases from the 17th century was twill weave found. The relatively loose fabric is typical especially of the 17th century, where it appeared 54 %, but it was frequent even in the first half of the 18th century. Very loose fabric of the net type with a structure of only 5x5 threads/sq. cm. was greatly popular around the middle of the 17th century. The density of c. 20 threads per cm was quite exceptional. (G. Carpioni) The ground is always coloured in the entire material, in a broad range of warm tones from ochre yellow to dark brown and almost black colour. According to period sources potters earths were used a  basic material which contain apart from ferric compounds that give the earth colour also colourless siliceous parts. An important source of information is the work by Giovanni Battista Volpato (1633 - 1677) Modo di tener nel Dipinger, in which the author describes the Venetian technique of the middle of the 17th century. For the preparation of the ground on the canvas he recommends potters earth called terra di boccali, ground in water and bonded with oil. It is applied with a spatula in two layers, with the upper one more finely ground. Local names for potters earths used for the preparation of the ground on the canvas are also given in the work of Francisco Pacheco, Arte de la Pintura, published in Seville in the year 1649. In the fifth chapter of Book III there is a mention of Seville earth, almagra comun. Palomino in part II of his book of 1724 describes on page 48 the preparation of the ground of earth called tierra de Esquivias and at the same time recommends, like Pacheco, the addition of lead white or umbra as a siccative in view of the fact that the medium of the ground contained oil An admixture of lead white was indeed found in the laboratory in a strikingly large number of grounds, although it does not show in the tints. The typical colour of the ground layer of 17th century Italian painting in our sample was deep brown, found in 45 %, a red to red-brown ground was found only in 19 %, a smaller share. The rest was formed of relatively light, ochre yellow grounds and, on the other hand, extreme dark almost black shades as well as a combination of two or more layers of different tone. The most frequent of the two layered grounds were made up of a combination of grey at the top and brown or red at the bottom. An exceptional find was a red intermediate layer placed between two brown coats. In the technique of panel painting, which is rather occasional, gesso with an admixture of chalk continued to the early 17th century. Light yellowish grounds could be localized to northern Italy and Venice, very dark ones were found in the Naples region. The mixture of yellow and brown ochres was often accompanied by an admixture of gypsum and chalk. In 18th century painting there was a predominance of a red ground of variously intense shades, found in 54 %. After the middle of the century the colour turned to bright orange tones especially in the region of Venice (Gasparo Diziani, Francesco Fontebasso). In the 18th century occasionally a light, yellowish ground of a mixture of gypsum and chalk began to be used (Sebastiano Ricci).

Our samples show that there were two bonding media of the ground in Italian Baroque painting. Laboratory tests confirmed the presence of oil as the main component, at the same time a frequent share of proteins was found. That means that a mixture of emulsion character was often used. That corresponds to historical sources which relate to the Italian region. Francisco Pacheco, who studied in Italy, recommended glue and oil as medium of the ground. The laboratory also searched for the presence of starch, which is mentioned in several sources, but without result. The medium was determined by staining the microscope section with a histochemical dye. In the National Gallery these analyses were carried out by Dorothea Pechová.

The materials of the ground layers are of considerable variety as research showed. It is difficult to distinguish artifical mixtures of ferric pigments of the type of ochre of different shades from natural earths, for in both cases the mixture contains siliceous components, even though of different grain.

We devoted special attention to the ground as the optical base of Baroque painting since the general tone of the picture is to a large extent dependent on this. In painting flesh, where semi-glaze coats appear in the modelling, on dark brown grounds there arise, according to the law of a turbid setting, optical greys that on red layers turn into a purplish tint. The painting on dark grounds presents a certain risk of the loss of semi-shades by raising the index of the refraction of the oil medium by aging if this phenomenon is not compensated for with light underpainting.

Baroque grounds, even if they contain ferric compounds, are relatively easily penetrable by X-rays. In two-layered grounds lead white contained in the grey layer shows a  more striking differentiation of the structure of the canvas. The painting and the brushwork can therefore be well studied on an X-ray picture. Valuable comparative material was gained in this manner the X-ray photos revealed also numerous changes made by the artist and marks of brushwork treatment of the lower layers of apparently smooth painting. The medium was studied only to a limited extent, mainly histochemically (see laboratory report) ... The analysed samples showed oil as the main component but the presence of protein was also proved.

The system of ground layers of Italian Baroque painting seems to be specific with their brown colouring of the basic layer which was predominant in the 17th century. A recent detailed analysis of French painting of the 17th and 18th century, on the contrary showed that in the course of these two centuries the red shade dominated in France 2. To judge by numerous minor studies 3 the same is true of Czech Baroque painting. But account must be taken of the frequent combination with a grey surface layer, which plays an important role in the optical structure of the picture.

  
1 Bolletino del Instituto centrale del restauro, Rome 1966

2 Alain R. Duval, Les préparations colorées des tablaux de l´école francaise des dix-septieme et dix-buitieme siecles Studies in Conservation 37, 1992, p. 239 - 258

3 V. Frömlichová, Malířská technika Karla Škréty (K. Škrétas Technique of Painting), in: Karel Škréta, exhibition catalogue, 1974

  JUSEPE DE RIBERA, ST. JEROME, DO 4374

All samples were taken from the right-hand margin of the picture. After being sealed in resin microscope sections were prepared. The layer system was dyed with black amide for proteins and Sudan Black B for oil. The pigments were demonstrated by microscope observation of their optical qualities and microchemical tests were added. In one case, sample No. 2, spectral analysis was added carried out in the restoration studio by Dr. Králová.

Ground: The yellow-brown ground contains yellow and red ochres, lead white and siliceous parts. The histochemical proof by dyeing on cross sections and the foam test are positive for oil.

Paint:
Sample No. 1 - background - the dark colour of the background is formed by a mixture of brown, black and red pigments.
Sample No. 2 - red draperies - the layer of red colour contains mercury red with an admixture of ferric red, red organic varnish, lead white and charcoal black. The mercury red was demonstrated in the spectral analysis by a conspicuous line on the spectral board in the area of mercury.
Sample No. 3 - white paper - the white painting was created with lead white and an admixture of black particles, probably charcoal black.

The medium of the colour layers was demonstrated by dyeing the sections widi histochemical dyes to which a foam test for oil was added. These tests proved the presence of oils and proteins.

  LUCA GIORDANO (1634 - 1705),
ST. SEBASTIAN, O 2421

Analysis of the ground layer from a sample of white drapery in the bottom right-hand corner of the picture and blue of the draperies.

The yellow-brown ground contains yellow and red ochres, lead white and siliceous parts. The histochemical proof by dyeing on a cross section and the foam test are positive to oil medium. On this ground layer lies the painting containing lead white and traces of smalt and charcoal black.

The analysis of the blue pigment of the draperies showed smalt (resistance to acids and alkali, isotropic in polarised light).

Smalt appeared in European painting roughly from the second half of the 15th century in one per cent of works. From 1500 to 1600 c. 22 %, and until 1750 20 %. After 1800 it appeared only in 1 % and then disappeared. (H. Kuhn, Doerner Institut).

  author
Mojmír Hamsík, AHVT A 041