| Silk cultural relics are not only important part of Chinese traditional cultural legacy, but also the useful datas to study our ancient cultures. However, silk cultural relics are easily to be damaged by light in exhibition for its weak character. The first step of light aging tends to be the fade of dyes in the surface of silk cultural relics. And therefore effective actions must be taken to protect the dyes from fading. So we carried out a series of systematic tests to study the lightfastness of the dyes—madder, sappan, cork tree bark, flos sophorae buds, indigo, gardenia and alkanna, which were very common in the history. Commercial silk was dyed by the seven dyes mentioned above, and then lightfastness of dyed silk was studied, which contained ultraviolet accelerated aging and general simulate aging. Finally, HPLC was used to analyze the internal mechanism of light aging of the chosen dyes.The rules of UV accelerating aging were similar to that of general simulate aging in irradiation of halogen lamp and LED lamp. It showed that UV accelerating aging can well simulate the light aging of dyes in irradiation of lights in museum. And the corresponding relationship between UV accelerated aging and halogen lamp aging is gained. In UV accelerated aging, the fading rules of dyes were analyzed comprehensively, which contained from jumping-off point of fade to the end. What's more, this paper analyzed the difference between continuous and discontinuous ageing. In general simulate light aging, LED lamp and halogen lamp aging were carried out to find the difference of light aging of dyes beween the two lamps. And possible effects were analyzed if dyes were in irradiation of fluorescent lamp. The energy of LED lamps focused on 450nm and 550~650nm, which will cause badly damage to the dyes absorbed lights in this wave band. So LED lamps were not suitable in illumination of silk cultural relics. Fluorescent lamps also focused on 450nm and 550~650nm, so it was not suitable in illumination of silk cultural relics either. Halogen lamps can be used as the light source in exhibition of the dyed silk cultural relics. But it released too much energy in part of infrared ray. Infrared antireflection can be used to reduce the irradiation of infrared ray. So that it can be more suitable in illumination of silk cultural relics.In halogen lamp aging, noticeable color shift of each dye was gained, and the lighting exposure in time of noticeable color shift was accounted. So fading of dyes can be avoided if the lighting exposure of dyed silk comes within its noticeable color shift. The lighting exposure in time of noticeable color shift was different from dye to dye. Madder: 30000lx·h; cork tree bark: 200000lx·h; flos sophorae buds: 3000lx·h; indigo: 300000lx·h; gardenia: 100000 lx·h; alkanna: 6000lx·h.The main colorant of each dye was identified by HPLC, and the relative curve between coloring matter and time was gained. The result showed that change of peak area of HPLC was consistent in the change of color difference. On these bases, a process was established to exactly analyze the degree of light aging of dyes in silk cultural relics by HPLC, which mainly depends on the change of peak area. When silk cultural relic is badly destroyed or its surface is not flat, the color difference is not easy to measure. In this condition, HPLC can be used to analyze the light aging of dyes, which is more exact and less sample is used in the test. The process of indigo light aging was brought up: indigo was attacked by singlet molecular oxygen under UV light, and it turned into peroxide intermediate product. The peroxide intermediate product was not steady, so it would break into Isatin quickly. The mechanism gained can provid more help in protection of silk cultural relics dyed by indigo. |
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