What is "adding alum" when painting and calligraphy are mounted?

Boil flour or starch into paste with water, which is paste.

Paste has a certain viscosity, and is mostly used to bond paper, cloth or articles. Modern production is mostly chemical paste made of cellulose and glue.

Using wheat starch as raw material, the consistency of the paste is starch ∶ water = 1 ∶ 6, the properties of the paste are relatively stable, and the cooking temperature is better than 80℃.

The purpose of adding alum to starch water is to promote the better precipitation of starch. Alum is not added to prevent corrosion when making paste.

It has three purposes:

First, dyeing silk with alum paste can prevent fading;

Secondly, the ink color of calligraphy and painting can be fixed with the paste supported by alum;

Thirdly, adding alum to paste inlay can avoid cracks. The author believes that alum should be used with caution in mounting new paintings, uncovering old paintings and restoring old paintings and calligraphy.

If alum is used too much, the mounted piece will be alum, which will increase the brittleness and hardness of the mounted piece, and make it difficult to uncover the mounted piece in the future, which is extremely unfavorable to the long-term inheritance of calligraphy and painting.