Centre for Sustainable Heritage, University College London, Gower Street, London WC1E 6BT, UK.
Talanta. 2010 Apr 15;81(1-2):412-7. doi: 10.1016/j.talanta.2009.12.017. Epub 2009 Dec 22.
Iron gall inks are of extraordinary historical significance considering their widespread use for over a millennium. Due to their corrosiveness, which is a consequence of their acidity and content of transition metals, iron gall inks accelerate the degradation of the writing or drawing support, which in this study is rag paper. Characterisation of acidity (pH) and degree of polymerisation (DP) of cellulose in paper is thus of high interest as it enables the estimation of material stability and assessment of risks associated with its handling. Based on a well-characterised set of samples with iron gall ink from the 18th and 19th centuries, we developed a near infrared spectroscopic method with partial least squares calibration for non-destructive determination of pH and DP of both inked areas and paper. Using this method, 27 18th and 19th century iron gall ink drawings from the British Museum collection were analysed and in all cases, inked areas turned out to be more acidic and degraded than the surrounding paper. Based on the obtained DP data, we were able to estimate the time needed for the inked areas to degrade to the point when they become at risk of damage due to handling. Using the average uncertainty of the calculated lifetime, we propose a quantitative stability classification method which could contribute to the curatorial and conservation decision-making process.
铁胆墨水由于其酸性和过渡金属含量的腐蚀性，在过去的一千年中被广泛使用，具有非凡的历史意义。铁胆墨水会加速书写或绘画支撑物（在本研究中是棉纸）的降解。因此，对纸张中纤维素的酸度（pH）和聚合度（DP）进行表征非常重要，因为这可以估计材料的稳定性并评估与其处理相关的风险。基于一组具有 18 世纪和 19 世纪铁胆墨水的特征良好的样本，我们开发了一种近红外光谱方法，通过偏最小二乘校准进行非破坏性测定墨水区域和纸张的 pH 和 DP。使用该方法，分析了大英博物馆收藏的 27 幅 18 世纪和 19 世纪的铁胆墨水绘画，在所有情况下，墨迹区域都比周围的纸张更酸，降解程度更高。基于获得的 DP 数据，我们能够估计墨迹区域降解到因处理而受损的风险点所需的时间。使用计算出的寿命的平均不确定性，我们提出了一种定量稳定性分类方法，这可能有助于策展和保护决策过程。
