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Many wooden artworks are contaminated by DDT (dichlorodiphenyltrichloroethane) as a result of a surface treatment by means of Hylotox-59©. The liquid preservative was used until the end of the 80s. DDT crystal structures are formed on the wood surfaces by the "blooming" of chlorine compounds. Contaminated waste wood with natural biocide ageing, gilded and wood carved elements of an old picture frame and wooden samples with paint layers were provided by the Schlossmuseum Sondershausen.
The removal of DDT was evaluated employing femtosecond and nanosecond laser radiation and cold atmospheric plasma technique using different working gases (air, nitrogen, and argon).
Before laser application, a chlorine measurement is done by X-ray fluorescence (XRF) analysis as reference. After laser processing, the XRF analysis is used again at the same surface position to determine depletion rates. Additionally, a documentation and characterization of the sample surface is done before and after laser and plasma treatment using optical microscopy. For plasma processing with various systems a chlorine measurement is done by gas chromatographic-mass spectrometry (GCMS) analysis.
For laser treatment a depletion of the chlorine concentration of 55-70% and 75% was achieved for 1064-nm nanosecond pulses and 800-nm femtosecond pulses, respectively. For the application of 30-fs laser pulses, no crystalline DDT residues remain on the sample surfaces. This holds also for the plasma processing with nitrogen as working gas.
Until the end of the 1980s many wooden artworks underwent surface treatment by liquid preservatives, e.g. Hylotox-59. DDT (dichlorodiphenyltrichloroethane) crystal structures are formed on the wooden surfaces by the "blooming" of chlorine compounds by time. In addition to an aesthetic disturbance, it is assumed that DDT represents a health risk. Therefore, the removal of DDT crystals from the surfaces is requested. Contaminated wood with natural biocide ageing, gilded and wood carved elements and wooden samples with paint layers were provided by the Schlossmuseum Sondershausen, Germany. Laser cleaning on selected surface areas on the objects was done by means of femtosecond and nanosecond laser pulses. For the same object, cleaning results using 30-fs laser pulses at 800 nm wavelength are compared to findings utilizing 10-ns laser pulses at 1064 nm wavelength. Before and after laser treatment, chlorine measurements at the same surface position were done by X-ray fluorescence analysis (XRF) as an indicator for the presence of DDT. In this way, pointwise chlorine depletion rates can be obtained for the different pulse duration regimes and wavelengths. Additionally, the object surfaces were examined using optical microscopy and multi spectral imaging analysis.