Leather dyes are predominantly sodium sulfonates of aromatic compounds (sometimes featuring carboxyl groups, -COOH) that form colored anions when dispersed in aqueous solutions. Characterized by small molecular size and strong penetrating power, they diffuse easily into the leather, facilitating thorough dyeing. Chemically, these dyes encompass various structures, including aromatic methane, quinone-imine, anthraquinone, azo, and nitro groups. They exhibit good lightfastness; furthermore, their negative charge makes them suitable for dyeing chrome-tanned and other metal-tanned leathers, which possess positively charged surfaces. They are effective for dyeing protein fibers (such as leather, fur, wool, and silk) as well as polyamide fibers. Given the diverse properties and processing methods associated with different types of leather, the choice of dye(s) and the application method must be tailored to specific dye-bath conditions. Manufacturers often market specialized leather dyes; for instance, certain 1:2 metal-complex dyes containing chromium or cobalt are suitable for spray-dyeing applications. These dyes are capable of directly coloring fibers—such as cotton, linen, and viscose—without the need for a mordant. Some varieties operate in acidic media to interact directly with the leather. While relatively inexpensive, these dyes have high molecular weights and slower penetration rates; consequently, their performance on leather fibers is often suboptimal, leading to their phasing out in the market. However, modern eco-friendly leather dyes are also available. The product discussed here is an acidic leather dye (specifically, an acidic composite dye). This series offers excellent performance characteristics, including vibrant color, rapid penetration, and high resistance to light and washing. Free from aromatic amines and heavy metals, these products are highly eco-friendly and represent a mainstream choice in both domestic and international markets. A wide variety of such dyes exists; therefore, when selecting leather goods, consumers should possess some basic knowledge and prioritize products made using high-quality dyes.