What is the role of ammonia in hair coloring?

The role of ammonia in hair coloring is primarily to open the hair cuticle for color penetration. When ammonia is present in a hair dye formulation, it increases the pH level, causing the hair cuticle to swell and lift. This swelling allows the color molecules to penetrate more effectively into the hair shaft.

By opening the cuticle, ammonia enables the hair dye to reach the inner layers where the actual coloring occurs. This process is essential for achieving a more permanent and vibrant result, as it allows the color to bond within the hair structure rather than just coating the surface. As the cuticles close during the oxidation process, the color becomes locked in, resulting in a long-lasting hair color.

In contrast, the other options do not accurately represent the role of ammonia. It does not provide color, condition the hair, or thicken the product, making the understanding of ammonia's primary function critical for effective hair coloring techniques.