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

在更接近纸质材料实际保存条件的条件下，进行了纸张的插入加速老化试验。本试验表明，酸性纸和碱性纸的界面变色较大。这一结果驳斥了传统的认为碱性纸更适合于酸性纸的保护处理的观点，受到了保护界的重视，当相对湿度增加到80%RH时，酸性纸发生了较大的变色。但在95%RH加压的情况下，变色率较低。在80°C和95%RH的压力下加速老化后，发现酸性纸中的SO4和Al组分迁移到相邻的中性或碱性纸质手册中。此外，当酸性纸插入碱性纸小册子时，钙也从碱性纸中转移出来。在较高的压力下观察到这些组分的迁移速度更快。酸性组分和碱性组分的迁移导致酸性纸的pH值升高，降低了酸性纸在湿热老化过程中的变色程度。通过碱性纸册的插入加速老化试验，即使在相同的纸的pH值下，含有硫酸铝的纸也比不含硫酸铝的纸表现出更大的变色趋势。鉴于几种商业碱性纸主要用于环保领域，我们考察了碱性纸和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pH值较低会导致插入的酸性纸变色较少。

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.