The CI number, or Chemical Identifier number, serves as a unique numerical designation assigned to every distinct chemical substance documented in the Colour Index. This system provides an unambiguous reference that eliminates confusion arising from similar or identical common names across different regions and industries. Essentially, it functions as the standardized passport for a specific pigment or dye, ensuring clear communication in scientific literature, regulatory filings, and manufacturing specifications.
Origin and Purpose of the CI System
Developed collaboratively by the Society of Dyers and Colourists and the American Association of Textile Chemists and Colorists, the Colour Index represents a global authority on colorants. The primary purpose of assigning a CI number is to create a universal language for the identification of colorants, bridging gaps between chemistry, toxicology, and manufacturing. This systematic approach allows regulators, formulators, and researchers to track the exact chemical composition of a pigment regardless of its brand or country of origin.
Structure of the Identification Code
Visually, the identifier is presented as "CI" followed by a five-digit number, such as CI 77019 or CI 15850. This numerical sequence is not arbitrary; it is organized based on the chemical class and color of the substance. The prefix acts as a constant marker, while the digits specify the exact entity within the database. This logical structure simplifies database searches and ensures that related compounds are grouped numerically, aiding in the identification of similar substances.
Classification and Organization
Within the vast database, substances are categorized primarily as either pigments or dyes. Pigments are generally insoluble particles that provide color through surface reflection, while dyes are soluble substances that color materials through absorption. The CI system further subdivides these categories based on chemical structure, such as azo pigments, phthalocyanines, or metal complexes. This granular classification is critical for professionals who need to understand the behavior, stability, and safety profile of a colorant.
Regulatory and Safety Significance
For regulatory bodies and toxicologists, the CI number is the definitive identifier used to assess the safety of a colorant. Legislation such as REACH in Europe and the FDA’s regulations in the United States rely on this number to verify compliance and restrict specific substances. When a safety data sheet (SDS) or a label lists a CI number, it guarantees that the information pertains to the exact chemical entity, preventing errors that could arise from vague naming conventions.
Application in Industry and Manufacturing
In the manufacturing sector, precision is paramount, and the CI number provides the necessary accuracy for formulators. Whether producing a lipstick, a car paint, or a printer ink, the recipe relies on the CI number to ensure batch consistency and color matching. Suppliers specify pigments using this code to avoid ambiguity, and quality control departments use it to verify that the correct molecular structure is being used in the production pipeline.
Utility in Research and Information Retrieval
For researchers and scientists, the CI number is an indispensable tool for literature reviews and spectral analysis. Databases like PubMed, chemical registries, and spectral libraries utilize this number to index data. When comparing the properties of a specific dye across multiple studies, using the CI number ensures that the researcher is analyzing the exact compound, thereby maintaining the integrity of scientific comparison and reproducibility.
