What is the difference between hot and cold blackening? - The difference between hot and cold blackening lies primarily in the temperature, process complexity, finish quality, and application suitability. Here's a detailed comparison: both hot blackening and cold blackening are metal finishing processes used to form a thin, black oxide film on the surface of steel (sometimes other ferrous alloys). The main differences lie in the process temperature, coating quality, durability, and cost. 1. Hot Blackening - Also known as: Hot black oxide, hot chemical bluing - Temperature: ~135–145°C (275–290°F) 1. Produces a deep, uniform black finish 2. Highly durable and wear-resistant 3. Excellent corrosion resistance (especially with oil sealing) 4. Suitable for industrial and high-performance applications 2. Cold Blackening - Also known as: Room-temperature blackening, cold black oxide. 1. Easy to use – no heating required 2. Ideal for small workshops, DIY, or touch-ups 3. Lower cost and safer handling 4. Simpler equipment setup. #Blackening Chemicals Manufacturer.