Procedures, methods and findings
During the course of the project the entire "Decius Mus cycle" is being extensively analysed to better understand the material usage and the painting technique(s) employed. Different imaging methods are used to document the work and help detect possible, earlier, modifications or changes in the painting procedure. In this process, the works are examined using rays of varying wavelengths (Ultraviolet , Visible, Infrared, X-rays).
X-ray imaging is additionally used to analyse the weave structure of the canvases. Alongside non-destructive methods such as X-ray fluorescence analysis (XFA) to identify pigments, minimal material samples are taken to determine the binding agents (oil/glue, etc.) through gas chromatography/mass spectrometry – GC/MS. Further paint samples will be embedded in resin and sectioned to show the layering of the original paint applications, and in cases the presence of later restorations. To determine the geological origin of the lead-based white pigment in the paintings, lead isotope analysis will be used.
Condition of the paintings
The “Decius Mus cycle” has been in the ownership of the Princes of Liechtenstein since 1693. Owing to the careful treatment of the paintings down the centuries, the condition of the whole cycle has hardly altered since its acquisition. From the end of the nineteenth century, earlier documentation of the painting’s condition and treatments record the consolidation and/or stabilization of paint layers and the re-saturating of the paint surfaces by varnishing. The latest procedure was undertaken in 1974, which involved strip-lining the edges to stabilize and tension the canvas supports.
Remarkably, two of the paintings – “Decius Mus Relating his Dream” and “The Death of Decius Mus” – are unlined and have exceptionally well-preserved paint surfaces. The reverses of these works thus offer a unique insight into the original structure of Rubens’s large-format canvas paintings. “The Death of Decius Mus” consists of seven vertical sections of canvas, joined with seams, adding up to a total length of more than five metres.
Painted inscriptions on the back of the paintings (transport information) are evidence that the other paintings in the cycle had already been relined in the seventeenth century, that is, before their acquisition by Prince Johann Adam Andreas I von Liechtenstein.
These (lined) paintings exhibit typical signs of distress caused by the excess moisture from the glue-paste adhesive during the lining process. These structural deformations are made obvious through compression cleavage (tenting) of the paintfilm, caused by the shrinking of the original canvas support. In addition, localized delamination between the lining canvas and original canvas has resulted in noticeable, localized undulations within the original canvas support.
Considering the rather large size of “Decius Mus Relating his Dream”, the canvas support is made with a very fine weave canvas, having a thread count of 21 per cm2. As the reverse has never been lined, it was possible to examine the hand-woven fabric and the original seams.
X-ray imaging and infrared reflectography show that Rubens first laid down his figures with underdrawing, sometimes shifting their position. A grid system was used to transfer the composition of the modello to the larger format.
All the compositions were originally painted in reverse (mirror image), as were the cartoons of the same dimensions, which were used as models for the weavers of the tapestries. The inscriptions (“SPQR”) were subsequently later painted over (non-reversed), so that the paintings could also function (later) as autonomous works.
Cross-section analysis using reflected light and scanning electron microscopy can reveal the structure of the ground and layers of paint, and identify the pigments contained in the samples.
X-ray fluorescence analysis (XRF) allows non-destructive identification of pigments directly on the painting. The material composition of a paint passage within a single site is analysed. The elements detected serve as a basis for interpretation of the pigments and extenders within the various layers of paint, allowing conclusions to be drawn as to the working palettes(s) of the studio.
X-ray fluorescence analysis and subsequent evaluation of the results were carried out in collaboration with Professor Dr Manfred Schreiner (Institute for Science and Technology at the Academy of Fine Arts Vienna).
Structural conservation of the supports
The lining canvas used for the painting “The Dismissal of the Lictors” had a missing portion of canvas measuring 15 x 30 cm in the lower left corner. This was caused by mice trying to get at the glue/paste adhesive used for the lining. As a stabilizing measure for the lining canvas and to reconstruct a unified support for the painting, the loss was repaired using a fabric intarsia. The material used for the repair was a fabric very similar in colour and structure to the original. After being cut to fit the loss exactly, the intarsia was attached to the original support with a glue/paste adhesive. The edges of the intarsia and the lining were aligned and secured with minimal amounts of a fibre-bulked, aqueous-based adhesive using fine tweezers and spatulas. After drying, the slightly lighter-toned bonding material was retouched to match the surrounding canvas. This method allows a large missing area to be stabilized in a relatively short space of time, using age-resistant materials that resemble the qualities of those used for the original artwork.
The painting “Decius Mus Relating his Dream” was damaged by a tear measuring 60 cm to the lower right area of the picture. In an earlier restoration the tear had been secured on the reverse with a strip of fabric (patch). Gaping apart by several millimetres, the edges of the tear had not been joined successfully but simply filled with gesso. Over time, the edges of the tear had released and deformed, emphasizing the fact that the mere application of a patch is inadequate for stabilizing damage to fabric in the longer term.
After assessing the condition of the canvas surrounding the tear, it was decided to employ a technique known as thread-to-thread mending or weaving. This technique, which has become an established practice in the last twenty years, was carried out in cooperation with Atelier Gerhard Walde. This procedure allows tears to be repaired and stabilized, with each severed thread being joined to the corresponding thread on the other side. To close the tear in the fabric, new canvas threads were attached to the horizontal and vertical ends of the original threads using minimal amounts of adhesive. These are then woven together and in keeping with the original alignment of the threads, glued to the ends of the threads on the opposite edge of the tear. The new threads are chosen to match the original canvas in terms of similar material qualities (fibre, tensile strength, colour). Because of the length of the tear and the extreme fineness and dense weave of the painting’s canvas, the repair was a time and labour-intensive process, carried out under a stereomicroscope with precision tools (surgical instruments). Lighter coloured points, resulting from thread-by-thread adhesion, and from the reverse of the canvas – caused by removing the patch – were then retouched to match the tone of the surrounding canvas.
Restoration of the paint surface
The paint surface of the “The Dismissal of the Lictors” exhibits numerous localized areas of retouching that have significantly darkened, as well as much larger, obvious passages of overpainting. Areas of damage, including an extensive tear at the lower left of the painting, have been covered by overfilling and overpainting in earlier restorations. All these interventions have been masked by numerous layers of degraded varnish. These older varnish layers fluoresce strongly under UV illumination, allowing limited interpretation as to the actual extent of reworking to the original paint passages. Nonetheless, the overpainted tear must have been repaired (by sewing) before the application of the lining canvas. It is conceivable that the filling and retouching that lie above this damage were carried out at the same time, strongly suggesting that some, if not all, of the extant retouching and overpainting could date to the seventeenth century.
Several tests were carried out in preparation for the removal of the overpainting and filling. The aim was to find an effective method for removal, but one that would not adversely affect the original paint layers. To help dissolve the layers of overpainting, thickened emulsions and solvent gels were utilized. In some cases, however, these mixtures were only able to swell the overpaint, which was subsequently removed mechanically under the stereomicroscope using fine scalpels.