Study of the Discoloration Mechanism at the Interface between Alkaline and Acidic Paper

在更类似于纸材料的真实的保存条件的条件下进行纸的插入加速老化试验。该测试表明，在酸性和碱性纸张的界面处经常发生较大的变色。研究结果反驳了传统观点认为碱性纸更适合酸性纸的保护处理，并受到保护界的重视。但在95%RH加压条件下，变色程度降低。在80°C和95%RH的压力下加速老化后，发现酸性纸张上的SO_4和Al组分向相邻的中性或碱性纸张上迁移。此外，当酸性纸插入碱性纸小册子中时，Ca也从碱性纸转移。在较高压力下观察到这些组分的更快迁移。酸性和碱性组分的迁移有助于酸性纸张的pH值升高，并降低酸性纸张在湿热老化过程中的变色程度。通过使用碱性纸张小册子的插入加速老化试验，即使在相同的纸张pH值下，含硫酸铝的纸张也显示出比不含硫酸铝的纸张更大的变色趋势。因此，可以说，不含硫酸铝的纸是最好的保护使用。由于几种类型的商业碱性纸主要用于保护领域，我们研究了碱性或中性纸对酸性纸变色的影响。因此，可以说，即使是质量好的碱性纸也会导致插入小册子中的酸性纸变色。假设碱性纸的较低pH值导致插入的酸性纸的较少变色。

Insertion-accelerated ageing test of paper in a condition that more resembles the real preservation condition of paper materials was conducted. This test showed that greater discoloration often occurs at the interface of acidic and alkaline papers. The result refutes the conventional idea that alkaline paper is preferable for conservation treatment of acidic paper and was received seriously by the conservation community.Larger discoloration of acidic paper occurred with the increase of relative humidity up to 80%RH. But in the case of 95%RH with pressure, discoloration was lowered. After accelerated ageing at 80°C and 95 %RH with pressure, it was found that SO_4 and Al components from the sheets of acidic paper moved to the adjacent sheets of neutral or alkaline paper booklets. Additionally, when acidic paper was inserted into an alkaline paper booklet, Ca was also transferred from the alkaline paper. Faster migration of these components was observed under higher pressure. The migration of acidic and alkaline components contributes to the pH increase of acidic paper and reduces the degree of discoloration of acidic paper during moist heat ageing.By insertion-accelerated ageing test using an alkaline paper booklet, paper containing aluminium sulphate showed a tendency for greater discoloration than one without it even at the same pH of paper. Thus, it may be said that aluminium sulphate-free paper is preferable for use in conservation.Since several types of commercial alkaline paper are predominantly used in the conservation field, we examined the effect of alkaline or neutral paper on the discoloration of acidic paper. As a result, it may be said that even good quality alkaline paper causes discoloration of acidic paper inserted in a booklet. It is assumed that lower pH of alkaline paper causes less discoloration of inserted acidic paper.