Ink we use

China discovered inks first though it was in use in Egypt by 2500 B.C. Later in the 10^th century, galls and iron was used to make ink. In modern manufacture of inks, tannic acid is used, and tannin was obtained by early man through the soaking of chestnut barks and galls. The tannin and iron mixture is insoluble when exposed to air. The iron is in the form of salt, usually ferrous sulphate. Inks has helped in the recording of historic events which we appreciate today.

Today, the quality of adhesion and scuff resistance of ink to paper surfaces could be verified by the Ink Rub Tester.

If iron is not enough as content, the writing fades. Original Chinese ink was made from soot and animal glue. For secret writing, the inks consist of colorless liquid like lemon juices which darken when the paper is heated.. Special inks are used in many applications and one of the example, is the ballot paper.