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

在更接近纸质材料真实保存状态的条件下，对纸张进行了插入加速老化试验。该试验表明，酸性和碱性纸张的界面往往发生较大的变色。这一结果推翻了传统的碱性纸更适合酸性纸的保护处理，受到了保护界的重视。当相对湿度达到80%RH时，酸性纸张的变色程度越大。但在95%RH和压力的情况下，变色程度降低。在80℃、95%相对湿度和压力下加速老化后，发现酸性纸张中的SO_4和Al组分转移到相邻的中性或碱性纸张上。此外，当酸性纸张插入碱性纸张小册子时，Ca也从碱性纸张转移。在较高的压力下，这些组分的迁移速度更快。酸性和碱性组分的迁移有助于酸性纸的pH值升高，降低酸性纸在湿热老化过程中的变色程度。通过插入加速老化试验，用碱性纸小册子，含硫酸铝的纸比不含硫酸铝的纸，即使在相同的纸张pH值下，也有更大的变色趋势。因此，可以说，不含硫酸铝的纸张更适合用于环保。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张，也会导致插入小册子的酸性纸张变色。假设碱性纸的pH值越低，插入的酸性纸变色越少。

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.