A German House Altar from the Sixteenth Century CONSERVATION AND RESEARCH OF REVERSE PAINTINGS ON GLASS

Prior to the conservation treatment of a late sixteenth-century South-German house altar with seven reverse paintings oil glass, technical and scientific research was conducted on the glass substrate, binding media, colourants and metals. Microscopic examination revealed the particularities of the so-called amelierung technique and the glass panel manufacture. For material analysis, gas chromatography-mass spectrometry, amino acid analysis, high performance liquid chromatography, as well as micro X-ray fluorescence spectrometry and scanning electron microscopy with energy dispersive X-ray microanalysis were applied. The main component of the binder was identified as a heat-treated pine resin (colophony), modified with various softening resins. The red paint layer contains cochineal and small amounts of dragon's blood. The original blue and green areas, which contain small and copper resinate, have undergone considerable colour change. The reverse paintings on glass were in a poor state of preservation: due to high moisture (flooding at the museum) and material degradation, the paint layers were severely delaminated, fractured into hundreds of small paint flakes and partially attached to silver foil and paper backing. The detached paint flakes were transferred back to their original positions oil the glass with a fine brush and secured using a hydrocarbon resin. This was followed by the application of microcrystalline wax which achieved a brilliant saturation of the reverse paintings on glass. However, the discolouration remained in the blue and green areas. A photograph of the altar's central panel after the conservation treatment was digitally manipulated to recreate the presumed original tonality.