The recently acquired Inmaculada by Pedro de Mena is being examined in the conservation workshop of the Liebieghaus Skulpturensammlung as part of a multiyear project sponsored by the Ernst von Siemens Kunststiftung. The primary goal is to free the sculpture’s high-quality original painting from its inferior overpainting. Damage to the carving and painting will also be treated, and the figure’s lost base construction and aureole will be reconstructed on the basis of comparative examples.

As in surgery, a detailed anamnesis and numerous preliminary examinations are carried out on the “patient” to be treated before the actual intervention. Only after the results have been analyzed can a conservational and art-technological diagnosis be made, on the basis of which a conservation concept is developed that is as gentle as possible.

The first step is a preliminary visual examination. In the case of the Inmaculada in the Liebieghaus, this was done both with the naked eye and under a stereo microscope. As a result, it was possible to get a rough idea of the elaborate construction and the state of preservation of the wooden structure. It also turned out that the polychromy underneath the overpainting was the original Baroque painting. This was a stroke of luck, as older layers of paint were often removed or damaged beyond recognition when sculptures were repainted.

The visual examination was accompanied by photographic documentation and a three-dimensional recording of the damage using photogrammetry. The digital 3D model has the great advantage of being able to capture areas of the sculpture that are heavily undercut or difficult to see.

The video shows how the initial condition and the damage to the sculpture before the interventions are recorded in three dimensions using photogrammetry.

One disadvantage of the optical preliminary examination is that it only records the exposed surface of the sculpture. However, many insights can only be gained by looking at the internal structures. The use of computer tomography and X-rays is particularly recommended for complex wooden constructions such as that of the Frankfurt Inmaculada. Thanks to the medical care centre Dr. Neumaier & Kollegen in Regensburg, CT scans could be made. These showed all the joints in the work block, which is made up of many wooden parts.

The video shows a computed tomography image through the side view of Pedro De Mena's Inmaculada.

In Pedro de Mena’s sculptures, this technique is perfected by hand. It can be seen that the separately carved skull of our figure, which measures only 5.5 centimetres in diameter and is inserted into the torso, is made up of several pieces of wood glued together.

Also clearly recognizable is the mask-like, hollowed-out front piece of wood with glass hemispheres glued to the back and painted from behind with an iris drawing. Such glass eyes were a common design element in Spanish Baroque, used to enhance the realistic effect of sculptures.

The many separately carved strands of hair and the onion-skin-like parts of the robe drapery attached to the work block could also be clearly identified and their attachment checked for originality. The numerous nails and puttying used in later conservation work can also be precisely located using the CT scans.

This information is invaluable to us conservators so that we can remove these later additions as carefully as possible. With the help of computer tomography (CT), it was also possible to clearly determine that the cloud on which the Frankfurt Inmaculada stands is a later addition: not only is it made from a single piece of wood, but it also runs over the original mounting channel through which the figure was once attached to its base by a threaded iron rod.

Particularly noteworthy is the CT scan of the crescent moon, which shows a face that is obscured by the cloud, a feature typical of Pedro de Mena’s Inmaculada type sculptures.

With the help of computer tomography, we can also assess the state of preservation of the Baroque colour scheme under the later layers of overpainting. The scans show a strong eyebrow drawing in the face, typical of de Mena’s Marian faces, and only a few imperfections in the skin painting.

In order to select or develop appropriate conservation methods, it is necessary to know the materials used in the production and subsequent conservation of the sculpture. This is done by taking very small samples of the material and analyzing them scientifically.

To determine the types of wood used, thin sections were analyzed macroscopically and under a light microscope at the Thünen Institute of Wood Research in Hamburg and compared with reference specimens. It was established that the robe drapery, the Virgin’s head and the crescent moon are made of pine wood (Pinus cf. sylvestris/nigra), a material frequently used in Spanish sculptors’ workshops in the 17th century. On the hands and hair strands, the wood species oleander (Nerius cf. oleander), previously unknown in Mena’s sculpture, has been identified.

The samples for the determination of the paint materials and binding agents of the original colour scheme and the later puttying and overpainting were prepared by the art technological laboratory of the Bern University of the Arts. For this purpose, the sample material was cast in a special synthetic resin and sanded. These so-called cross-sections were then analyzed and documented using light microscopy (VIS/UV) and scanning electron microscopy (SEM-BSE) under different lighting conditions. The various pigments and binders were analyzed using infrared spectroscopy (FTIR-ATR), IR spectroscopy (chemical imaging) FTIR-FPA and X-ray spectroscopy (REM-EDS).

The results confirmed that the lowest layer of paint is the original Baroque painting, done in a style which can also be found on other sculptures by Pedro de Mena. At the same time, the exact layer structure and the composition of the primer and paint layers were determined, which is essential for the development of the complicated removal of the overpainting using mechanical and chemical processes. The investigations show that the later reworking of the sculpture must have taken place at different times. The most recent can be dated between the mid-19th and early 20th centuries, based on the choice of materials and the porcelain doll-like aesthetic of the skin painting.

After the preliminary art-technological and scientific analyses, it is clear that the Baroque painting not only differs from the later overpainting in its colour concept, but also far surpasses it in terms of its artistic and technical quality. Beneath the sculpture’s glossy, plastic-like layers of overpaint, an outstanding example of Pedro de Mena’s virtuoso painting technique has been preserved. This will be described in more detail in a forthcoming article and illustrated with the first exposure probes. The methods developed to remove the overpainting will also be explained in detail there.