Study On The Non-Destructive Analysis And Identification Of Pigments On Color Relics And Protection Materials

The main job in color relics studies and protection is to identify pigments and toconsolidate surfaces.Ideal relics analytical techniques should be non-destructive because cultural heritages havethe special characteristic of un-rebirth. Nowadays some commonly used analytical methods,such as XRD and XRF etc., need to take some samples from relics or need to prepare propersamples for identification, which brings about some damages to relics absolutely. Some kindsof fiber optics reflectance spectrophotometers have been used to identify pigments abroad, butit is difficult for the most Chinese museums and cultural relics departments to afford as theseinstruments are too expensive.Another problem to be solved urgently for color relics is surface protection andconsolidation. Although more and more organic polymers have been applied to the field ofrelics protection, there is so little systemic, scientific and complete research on materials'stability that it is blind and unilateral to choose relics protection materials.In order to meet the special demands of protecting relics, taking into account the situationin China, we have refitted a domestic instrument to a fiber optics reflectancespectrophotometer with low price and good function to identify pigments without any damage.With our self-made fiber optics reflectance spectrophotometer, we analyzed composition ofpigments on color relics in Dazu Stone Sculpture Area, Chongqing and Yangling Museum ofHan Dynasty. On the basis of investigating their stability, we have improved theanti-photoageing property of these color relics protection materials through addingUV-absorbers by a physical mix.In this thesis, we have developed a simple fiber optics reflectance spectrophotometer byrefitting from a domestic spectrophotometer, model 72G. It consists of a tungsten lamp, amonochromator, an optical fiber, a shielding chamber, a photomultiplier tube, a reading meter,a high voltage supply source. Here, (1) to assure non-destructive measurement a glassbifurcated optic fiber is used to transfer light. (2) this spectrophotometer can detect a weakreflectance signal as a photomultiplier tube substitutes for a photoelectric cell as the detector. (3) a metal shielding chamber has been designed to eliminate the light interference fromoutside, so it enhances accuracy of the measurement. Compared with Perkin-Elmer Lambda17 UV-Vis spectrophotometer, our instrument with stable performance has qualified forpigment identification on relics. Through analysis on a great variety of Chinese ancientpigments, we have deduced three reflectance spectrum shapes of pigments, bell-shaped,s-shaped and oblique line-shaped. Also, we have found out the reflectance spectrumcharacteristics of every pigment and the factors affecting on the reflectance spectra of thepigments, including the saturations, the grain sizes of the pigments, the adhesives in them,their underlying layers and the protection materials over their surfaces and so on. A basicanalytical method is established, in which we identify pigments on color relics by comparingtheir shapes of reflectance spectra and positions of reflectance peaks or first derivative peakswith those of related standard pigments.With our self-developed spectrophotometer, pigments on One Thousand Hand Buddha inDazu Chongqing, color pottery figurines of Han dynasty, frescoes from the tombs in Chang'anCounty etc. have been identified. It has been indicated that the results of relics pigments withfiber optical reflectance spectroscopy are accurate and reliable, verified by XRD and XRF.Eight polymeric materials'changes on color, molecular structures, surface configurations,hydrophilicity, physical intensities have been investigated systematically by diffusereflectance spectroscopy, FTIR spectroscopy, microscopical analysis, contact angle, hardnessduring UV-irradiation. According to these data, the anti-photodegradation abilities areassessed and the degradation mechanisms are also deduced. These relics protection materialsbelong to four kinds. They are:①polyurethanes, including TDI-polyurethane,MDI-polyurethane and HDI-polyurethane;②poly (acrylic acid)s, including poly (acrylic acid)varnish, Primal AC 33 and B72;③the organic-silicon;④the epoxy-resin. In our experiments,an UVB-lamp was selected as artificial weathering source. It has been showed that amongthese four kinds of materials poly (acrylic acid)s, especially Primal AC 33 and B72, as the bestrelics protection material, has the best anti-photodegradation property and is valuable to useextensively.In order to enhance the anti-photodegradation of these relics protection materials, B72,MDI-polyurethane and the epoxy-resin have been modified firstly with the UV-absorbers, UV-326, UV-327, UV-328, UV-531 and UV-P by a physical mix.The results have indicated that these UV-absorbers are stable with the weight loss ofmore less 1.0% under UV-irradiation for 70h. The characteristics of color, FTIR spectra,hardness, weight loss and reversibility have all been improved after the modification. The bestconcentration of UV-absorbers is 0.5%～3%. Considered above factors comprehensively, theoptimum plans about the modification of three systems have been selected, that is B72modified with 3%UV-327, MDI-polyurethane modified with 0.25% UV-327 and 0.25%UV-531 or 0.25% UV-328 and 0.25% UV-531, the epoxy-resin modified with 3% UV-328.