以紅外線與固態核磁共振光譜探索古代樂器木材特性

Abstract

克里蒙納提琴獨特的原因一直是科學家們試圖解答的問題，然而往往無法得到結論性的答案，在本實驗室先前的研究中提出可能是由於製琴時對木材的化學前處理，加上木材自身老化與長期高頻振動使得這些名琴的音色如此獨特。因此本篇將以衰減全反射-傅立葉變換紅外光譜（ATR-FTIR）與13C多重交叉極化核磁共振光譜（13C multiCP NMR）對木材的自然老化做更深入的研究。木材的老化自被砍伐的當下就持續進行，會受到環境條件及負重程度影響其老化速度，而本研究使用保存環境相似、且較無負重問題的多把兩、三百年提琴與千年古琴之樂器用木材樣品，試圖找出木材自然老化的規律。透過紅外光譜與碳譜分析，配合樹種鑑定、古物特徵與碳十四定年結果，本篇將楓木（Acer spp.）、雲杉（Picea spp.）、杉木（Cunninghamia lanceolata）、泡桐（Paulownia spp.）、青桐（Firmiana spp.）和梓木（Catalpa ovata）等樹種之木材老化對化學成分影響的研究延伸至千年的範圍。本研究也將現代木材進行化學處理，將之加速老化，並試圖與自然老化木材相比較。此外，先前的研究中指出部份克里蒙納名琴內有較高的鋁含量，且在27Al固態核磁共振光譜（27Al ssNMR）中更是有特殊的四配位（IVAl）及五配位（VAl），因此本篇將接續此項研究，使用現代木材與多種化學試劑，試圖獲得與名琴相似的化學環境，並初步再現了名琴木材中獨特的IVAl。

What is it that makes the instruments of Cremona school unique? Many scientists have attempted to answer this question. However, no study has found a conclusive answer. In our previous study, we pointed out that chemical pre-treatment for the violin processing may be a crucial reason. In addition, the combination of natural aging of wood and long-term high-frequency vibration of the violin may cause special chemical and structural changes in the Cremona instruments. Hence, this study will further focus on the natural aging of wood by using attenuated total reflectance (ATR) FTIR and 13C cross-polarization magic angle spinning NMR, supported by species identification and carbon 14 dating. The aging of wood begins with the cutting of the tree, and the decay rate of wood materials depends on environmental conditions, including temperature, humidity, or the exposure to mechanical stresses. The samples used in this study are violin and Chinese guqin wood samples, which are specially selected tonewoods under optional storage conditions. Several kinds of wood had been analyzed in this study, including maple (Acer spp.), spruce (Picea spp.), fir (Cunninghamia lanceolata), paotong (Paulownia spp.), qingtong (Firmiana simplex.), and catalpa (Catalpa ovata). By comparing these samples, the timeline of the chemical composition changes in wood during one thousand years of natural aging can be mapped out. Some artificial processes had also been applied to modern tonewood samples to accelerate aging and compared with the natural aging. Also, in our previous study, it has been found that some Cremonese samples have high Al content and some of the samples exist in special four- and five-coordination states according to 27Al ssNMR. This phenomenon was also examined in this study. It is observed that four-coordinated aluminum can be partially generated by soaking modern wood in alum solutions followed by alkaline treatment.