The dye colours the leather without producing the uniform surface of a topcoat paint or insoluble pigmented sealant, as on other leathers, and so retains the hide's natural surface.
[1] For this reason, only high-quality leather is suitable for aniline finishing.
Originally, the dyes used for this process were synthesized from aniline through chemical reactions.
In modern times, the dyes used are subject to laws and regulations in many countries, and the use of certain azo compounds is prohibited in the European Union as there are reasons to assume health risks.
Semi-aniline leather is produced through a very similar process to full-aniline, but has a thin protective top coat added to protect it from wear and staining.