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Blackens steel and iron parts (not stainless steel). Parts must be sealed after blackening. Use our Penetrating Sealer or Caswell Sealer.
Thoroughly clean the part to be blackened by either sandblasting, wire brushing, wire wool abrasive cleaning, or by scrubbing in ‘VIM’ or ‘COMET’ household abrasive cleaner. Make sure you have removed all rust, paint, oil and grease. Must be used on Clean bare metal. NOTE: Mill scale or heat treat scale must be removed prior to blackening in order to achieve the best and most uniform finishing results.
Mix 1 part Concentrate with 9 parts distilled water. 1 pint of concentrate makes 1.25 gallons of blackening solution. Parts Coverage – 600 to 1200 sq. ft. of surface area blackened per gallon of concentrate.
Immerse the part in the mixed Black Oxide Solution and swirl around for between 30 seconds and 5 minutes. Alternatively, the part may simply be placed in the solution for 5 – 10 minutes. Remove the part from the solution and rinse in fresh water. Use at room temperature.
Some hardened or specialized steels will not readily accept the blackening process. Activation can be done using a 10% sulfuric acid (not sold by Caswell) and distilled water etch 2 to 5 minutes, then thoroughly rinse before immersing into the black oxide. To enhance blackening effect warm the part to approx. 120 deg F, or warm the liquid to 80 deg F before use.
Some hardened and specialized steel alloys may blacken to a deeper black finish when activated using our Black Oxide Activator.
Make a small test batch first to ensure the 9:1 dilution will work with your process, some parts may require a stronger mixture i.e. 4:1 or 2:1. Brush on or spray method may also require a stronger mixture.
Black oxide is not a high corrosion-resistant coating. The corrosion resistance comes from the top coat, which can be one of the following, penetrating oil, sealer concentrate, wax or clear coat can all be used. It is not suitable for severe outdoor applications or corrosive environments.