Acid Blue 90, also known as Acid Blue AS, serves as a dye and coloring agent in various industries. Its primary function is to impart a blue color to a wide range of materials, especially protein-based fibers such as wool, silk, and nylon. Some of the key functions of Acid Blue 90 include:

1. Dyeing: Acid Blue 90 is used for dyeing textiles and fibers, including wool, silk, nylon, acetate, and polyester. It can create various shades of blue, depending on the concentration and application method used. The dye molecules attach to the fibers through ionic and hydrogen bonding, resulting in a durable and wash-resistant color.

2. Printing: Acid Blue 90 is also used for printing designs and patterns on fabrics. It can be applied through techniques such as screen printing, roller printing, or digital printing to create intricate and vibrant blue designs on textiles.

3. Leather Dyeing: Acid Blue 90 finds application in the leather industry for dyeing leather products, including shoes, bags, belts, and garments. It can give a blue color to different types of leather, enhancing their aesthetic appeal.

4. Paper Dyeing: Acid Blue 90 is sometimes used to impart a blue color to paper products, such as specialty papers, crafts, and artworks.

5. Indicator: Some acid dyes, including Acid Blue 90, can also act as acid-base indicators. They change color in response to changes in the pH of the surrounding environment. However, Acid Blue 90 is primarily used as a dye and does not serve as a highly accurate pH indicator like specific indicator dyes.