A hardener is a chemical used during the fixing stage of photographic processing to strengthen and toughen the film's emulsion. This makes the emulsion more durable and less susceptible to scratches or physical damage during handling and drying.
Hardeners are particularly useful in traditional darkroom work, especially when processing film or prints that require extra protection. Understanding the role of a hardener helps photographers maintain the integrity and longevity of their negatives and prints, ensuring high-quality results.