How is litmus paper made?

Litmus paper is made from lichens. Lichens are unique in that they are actually two distinct organisms, a fungus and an alga, living as one. Botanists classify lichens as fungi because it is the fungi that are considered to be responsible for sexual reproduction.

Approximately 15,000 different types of lichens have been identified. Lichens can be found growing on rocks, trees, and walls, in the soil and even under water in virtually all types of climates. Lichens are commonly used as gauge for environmental quality because they are sensitive to various pollutants. Several varieties of lichen are used to produce litmus. In fact, the Netherlands is one of the largest producers of litmus paper products.

The production of litmus paper has many features in common with paper manufacturing. In this process, the wood pulp is converted to paper, the paper is infused with the lichen solution, and the paper is dried and packaged.

Litmus paper is available in both red and blue varieties. The natural color for litmus paper is blue. When put in an acidic solution the blue paper turns red. Red litmus paper is first mixed with an acid when it is made. This causes the paper to appear red. When put in the presence of a base, the paper returns to its natural blue color.