lundi 29 Mar 2021

Photogrammetry is a low-tech technique that can be used to create a precise 3D rendering of an artefact without having to resort to traditional molding techniques. It is of particular interest for very delicate structures that cannot be handled during the process. Objects of all sizes can be treated. The resulting 3D model can be used for the off-location study of the artefact, for establishing condition reports, for monitoring surface alterations, for creating adapted supporting structures for storage and transport as well as the recreation of missing parts.

Equally of interest is the exact rendering of the surface topography that can be viewed with or without colour, allowing a greater precision when assessing surface textures. UV and infra-red images can be integrated in a second step and superposed on the existing surface topography.

For the DOA project the aim was to carefully document the initial condition of the cartonnage case before any intervention was made. This was done in order to document possible changes during transport or handling and to permit a high resolution restitution of the complex surface for an initial condition report. For that 800 high-resolution photographs were taken from various angles by Andreas Hochuli (HKB). These were uploaded to the Metashape (Agisoft) software that reconstructed each photograph, transforming them into scaled models with approximately 120 million surface points. The result is a high-precision virtual model that can be examined from all sides and allows to zoom into areas of particular interest.

The technique will also be used at the end of the project when an adapted supporting structure will have to be made for the upper cartonnage case.

Visualisations will be uploaded soon

Temporary stabilization

mardi 23 Mar 2021

When the cartonnage case was cut open at the beginning of the 20th century its structural integrity was lost. Years of manipulation uncontrolled storage have left a distorted and weakened two-piece cartonnage case with the mummy . The result was delamination, creases and tears in the cartonnage case as well as lifting and loss of paint (Figs. 1 & 2). The extreme fragility of the cartonnage case made handling and transport from Brissago to Neuchâtel impossible.

Not wanting to introduce a consolidant into the paint layers before having the opportunity to study them we looked for a temporary consolidant that could be removed at a later date without leaving any residues. Preliminary analysis of the polychrome layers at the HKB by Dr. S. Zumbühl & Dr. N. Scherrer confirmed the absence of non-polar components. As a result, cyclododecane (C12H24) was chosen as a temporary consolidant. At room temperature cyclododecane, a saturated cyclic alkane, is a white waxy solid with slight odor. Applied in a melt or dissolved in a non-polar solvent it can consolidate fragile surfaces for a finite amount of time. As it sublimates at room temperature, the adhesive will diminish over days and completely disappear over weeks.

Cyclododecane was applied to the polychomy of the cartonnage with micropipettes in a melt (58°C) with small addition of petroleum ether (100-140°C boilng point) to slow down its solidification (Fig. 3). It was applied before transport and again some weeks later when the upper part of the cartonnage was lifted off the mummy with the help of a custom-made frame (Fig. 4).

Figure 1. Creases and loss of paint in the middle section of the cartonnage case
Figure 2. Creases and flaking paint in the chest area
Figure 3. Students of the HE-Arc CR consolidating the paint layers and cartonnage case with cyclododecane
Figure 4. Removal of the upper part of the consolidated cartonnage case with a custom made support frame
Figure 5. The interior of the much flattened lower part of the cartonnage case after removal of the mummy

Figure 1 et 2 : photographs Schreyer
Figures 3, 4 et 5 : photographs HE-Arc CR