Presto Black STEEL PC9 concentrate - Deep blue/black finish

In this review of Presto Black STEEL PC9 the bottom line is simple: this concentrate is for makers, restorers and metalworkers who need a quick, controllable way to produce a deep blue/black patina on ferrous metals. The single biggest reason to buy is its flexibility as a concentrate that can be mixed for brush-on or immersion use, allowing small touch-ups or full-part immersion with predictable blackening. The reviewer found it fast to begin working on clean steel and useful for producing a uniform black oxide look when followed by a proper post-seal step.

Key Features

• Concentrate formulation: Mix at 50/50 with water for brushing or about 10% for immersion to control penetration and color depth.
• Versatile application methods: Can be applied by immersion, swab-on, or spray so it adapts to both small repairs and larger parts.
• Fast-acting reaction: Black color begins to develop instantly on clean steel surfaces, enabling small projects to finish in minutes.
• Customizable finish: Stronger concentrations produce faster, darker blackening and allow handling difficult-to-blacken surfaces.
• Compatible with sealants: The conversion black surface accepts oil, wax, clear coats and lacquers to lock in appearance and slow rusting.
• Made in the USA: From a long-standing brand used in architectural and artistic work since 1948, offering predictable manufacturing quality.

Who It's For

This product suits hobbyists restoring tools, machinists touching up parts, artists creating patinaed pieces, and DIYers building small black oxide kits. The concentrate format is particularly good for users who want to dial in concentration for either delicate swab-on work or full immersion of parts.

Those who need corrosion protection out of the bottle should look elsewhere; the coating itself does not prevent rust and requires immediate drying and a separate sealer. Also, this is not intended for stainless steels so buyers working primarily with stainless should choose a different process.

Pros & Cons

Pros

• Easy to mix and apply with predictable blackening on iron and non-stainless steels.
• Flexible application methods make it useful for both small touch-ups and larger parts.
• Fast color development reduces project time for small jobs.
• Accepts a wide range of sealants so the finish can be preserved once sealed.

Cons

• Does not provide rust protection by itself and requires immediate drying and sealing to avoid flash rusting.
• Color results can vary by steel type and prep; some users report a dull or grey/blue tone rather than a deep black on certain surfaces.

Specifications

Product type	Blackening concentrate for ferrous metals
Mix ratios	50/50 water for brush-on; ~10% in water for immersion
Suitable metals	Steel, iron, cast iron (not stainless steel)
Application methods	Immersion, swab-on, spray
Finish	Blue/black patina similar to cold blue
Origin	Made in the USA
Post-treatment	Requires drying and sealing with oil, wax, clear coat, or lacquer

Our Verdict

Presto Black STEEL PC9 is a practical, value-oriented blackening concentrate for anyone working with ferrous metals who needs control over application method and color intensity. It is fast and versatile for touch-ups and small production runs, but users must plan a follow-up drying and sealing step because the conversion finish itself does not stop rusting.

Frequently Asked Questions

Will this blacken stainless steel?
No. It works on iron and non-stainless steels, but it will not blacken stainless steel.

Do I need to seal after blackening?
Yes. The conversion does not protect against rust; parts should be dried and sealed with oil, wax, clear coat or lacquer to prevent flash rusting.

Can I use it for small touch-ups?
Yes. The concentrate can be mixed 50/50 for brush-on or swab application, making it convenient for small repairs and details.