Black Oxide Finish Service

Our black oxide finish services deliver durable rust protection and a sleek matte black look—perfect for metal parts needing both resilience and visual appeal. We apply precision black oxide treatments to boost longevity and elevate aesthetics, with results you can rely on.

Rust-Resistant Black Coatings
Sleek Matte Finish for Metal
Durable Oxide Treatments

Inquiry Now

(Click to Enlarge)

Other Surface Treatment Services

What is Black Oxide Coating & How Does it Work

Black oxide coating is a chemical process that converts the surface of ferrous metals (like steel) into a thin, matte black oxide layer—typically magnetite. Unlike plating or paint, it transforms the metal’s top layer rather than adding a separate material, creating a tight, durable bond. Other industry terms and trade names for black oxide include gun bluing, blackening, Black N, black passivating, Black Magic, and black penetrate. It’s prized for corrosion resistance, reduced friction, and a sleek black finish, ideal for tools, hardware, and industrial parts.

Black oxide coating processes are categorized by temperature: high (120–140°C), mid (70–100°C), and low (room temp to 50°C). Each uses different solutions, suited to varying part needs—from durable, high-wear components to heat-sensitive or small parts. After treatment, all are sealed with oil or coating to boost corrosion resistance, resulting in a thin, long-lasting finish.

3 Types of Black Oxide Finishing Process

Hot Black Oxide

Hot black oxide uses a hot alkaline immersion process, forming a uniform oxide layer 0.5–2 µm thick. This method is highly efficient, making it ideal for heavy-duty applications like tooling, automotive parts, and military hardware—where durability and consistent protection against wear are critical.

Mid-Temperature Black Oxide

Mid-temperature black oxide relies on lower-temperature immersion, producing a consistent 0.3–1 µm coating. With moderate-high efficiency, it’s well-suited for precision components and electronics hardware, as its milder temperature minimizes thermal stress on sensitive parts.

Cold Black Oxide (Room Temp.)

Cold black oxide involves chemical immersion at room temperature, resulting in a thin 0.1–0.5 µm coating. Operating at moderate efficiency, it’s primarily used for decorative items and small fittings, where a sleek, low-profile finish is prioritized.

(Click to Enlarge)

6-Step Process

Here’s how to apply black oxide:

Prep & deburr: First, machine parts to specification and remove burrs to ensure a smooth surface.
Clean thoroughly: Use alkaline solutions to strip oils, contaminants, or residues—critical for proper oxide adhesion.
Rinse: Wash parts with water to remove cleaning agents.
Black oxidizing: Immerse parts in a temperature-specific chemical bath (hot: 135–145°C; mid-temperature: 70–100°C; cold: room temperature) for 5 to 40 minutes, with duration adjusted based on part size and oxide type.
Rinse again: Remove excess bath solution with a water rinse.
Seal & finish: Treat the oxide surface with oil, lacquer, or wax to lock in the finish, enhance aesthetics, and boost corrosion resistance.

MIL-C-13924 Black Oxide Coating Standards

As a manufacturer specializing in black oxide coating services, we adhere strictly to industry standards to ensure consistent quality. The MIL-C-13924 standard is a key reference for our processes, outlining specific requirements for different coating types and material compatibilities. Below is a clear breakdown of its core classifications—including versions, classes, and applicable materials—to help you understand the specifications we follow in our production.

Standard Version	Details
MIL-C-13924C	No dimensional changes occur during the coating process.
Class 1	Alkaline oxidizing treatment. Suitable for wrought iron, cast/malleable irons, plain carbon steels, and low-alloy steels.
Class 3	Fused salt oxidizing treatment. (Not offered at TPP.)
Class 4	Alkaline oxidizing treatment. Exclusively for 300-series corrosion-resistant steel alloys.

cnc machined metal part with black oxide finish

Applicable Materials

Material Category	Specific Types	Key Characteristics & Notes	Model Examples (Common Types)
Ferrous Metals	Carbon Steel	Core material; forms matte-black magnetite layer; requires oil/wax post-treatment	1018, 1045, S235JR, Q235
	Alloy Steel	Compatible; high-Mn alloys may show red/brown hues	4140, 34CrMo4, 30CrMnSiA
	Stainless Steel	Enhanced corrosion resistance; typically no post-treatment needed	304, 316L, 0Cr18Ni9, X6CrNiMo17-12-2
	Cast Iron	Requires thorough cleaning of surface porosity	HT200, EN-GJL-250
	Powdered Metal	Resin impregnation mandatory to seal pores	FL-4605, FL304-260N, FX-08C20
Non-Ferrous Metals	Copper & Alloys	Forms copper selenide layer; verify post-treatment needs	C11000, C26000, T2
	Zinc & Alloys	Cold process only; high-temp causes deformation	ZnAl4, ZL043A
	Brass	Compatible only with specific alloys (e.g., low-zinc types)	C36000, HPb63-3, CuZn39Pb3
	Aluminum & Alloys	Restricted: Cold process feasible; high-temp damages material	6061-T6, 2A12, AW-6082

Other Metal Materials

Why Choose Black Passivation For Your Metal Part

Minimal Dimensional Impact

Unlike plating or painting, which introduce additional layers that can disrupt measurements, black oxide transforms the metal’s surface inherently. This avoids thick coatings and eliminates dimensional deviations, making it ideal for tight-tolerance components such as precision gears, tooling, and parts requiring exact fits.

Superior Corrosion Resistance

The oxide layer forms a natural protective barrier. If it is further sealed with oil or wax, its anti-corrosion and anti-oxidation capabilities will be further enhanced. This ensures that components used in outdoor, high-humidity or damp exposure environments can have a longer service life, thereby reducing the need for frequent replacements.

Reduced Friction & Wear

The smooth, dense oxide film minimizes friction between interacting metal parts—such as hinges, sliding mechanisms, and mechanical linkages. Reduced friction lowers galling and wear, enhancing the durability and performance of mechanical systems.

Versatile Aesthetics & Compatibility

Its matte black surface treatment combines practicality with visual appeal: it is sturdy and durable, suitable for heavy-duty tools and automotive parts; it also has smooth lines, making it suitable for decorative hardware and electronic products. It is compatible with most iron-based metals and ensures consistent performance on different sizes and types of parts.

Applications of Black Oxide Coating

Automotive Industry

Black oxide coating enhances corrosion resistance (up to 50% improvement) and maintains dimensional stability for components in complex operating conditions, such as transmission gears, half-shaft drive shafts, and chassis fixing bolts.

Military and Defense

Black oxide treatment provides long-lasting corrosion protection for equipment parts while significantly reducing surface reflection (glare reduced by over 90%) to enhance concealment, including rifle receivers, tactical helmet metal fittings, and military communication equipment terminals.

Tool and Hardware Industry

Black oxide coating improves wear resistance and extends service life (approximately 30% longer) of components while enhancing aesthetic quality, such as torque wrench bodies, door/window hinge pins, and water pipe valve handles.

Precision Instrument Field

Black oxide treatment protects part surfaces without compromising dimensional accuracy, meeting the needs of high-precision operation, including optical microscope adjustment gears, aviation instrument pointer shafts, and metal valve cores of medical infusion pumps.

Frequently Asked Questions

Is it possible to select only the areas with black oxide coating instead of coating the entire surface?webadmin2025-07-10T07:43:19+00:00

Is it possible to select only the areas with black oxide coating instead of coating the entire surface?

Yes, black oxide can be applied selectively—this is done by masking off areas that don’t need the coating before processing.

The key is using masking materials that resist the specific black oxide bath (whether hot, mid-temperature, or cold). For example:

High-temperature processes (120–145°C) often use heat-resistant materials like silicone rubber plugs (for holes) or fiberglass-reinforced high-temp tape to cover flat surfaces.
Mid or cold processes may use standard chemical-resistant tapes, wax-based masking compounds, or even custom rubber masks, as they don’t need to withstand extreme heat.

Once masked, the part is submerged in the oxide bath. Only the unmasked areas react with the solution to form the black finish; masked sections stay untouched. After treatment, the masking is removed, leaving precise, selective coating.

This technique is useful for parts needing mixed finishes—like a gear where teeth require black oxide for wear resistance, but a shaft end needs to stay bare for welding or electrical conductivity.

Is black oxide available in colors instead of black?webadmin2025-07-10T07:39:55+00:00

Is black oxide available in colors instead of black?

Black oxide treatment only creates a uniform matte black finish—you won’t get other colors from this process.

If you need different hues, though, other surface finishing methods are better options. Things like anodizing, powder coating, or electroplating can deliver a range of colors, plus extra protective properties.

To figure out which alternative works best for your needs, talk to a surface finishing provider. They can break down the options and help you choose.

How long does the black oxide treatment process take?webadmin2025-07-10T07:38:13+00:00

How long does the black oxide treatment process take?

Black oxide treatment, from cleaning to sealing, usually takes 1 to 3 hours. How long exactly depends on the process type—hot, mid-temperature, or cold—and the size of the parts. Plus, we can handle batches, so multiple components get processed efficiently at the same time.

Is black oxide coating environmentally friendly?webadmin2025-07-10T07:36:09+00:00

Is black oxide coating environmentally friendly?

Black oxide coating is fairly eco-friendly with today’s processes.

We use tightly controlled alkaline or acidic solutions, recycling baths to cut waste and treating leftovers to neutralize harmful stuff before disposal. This means way fewer heavy metals or toxins compared to some plating methods (like chrome plating, which makes risky byproducts).

It also beats paint finishes, which often release volatile chemicals. And by sticking to strict environmental rules, we keep its impact low.

How long does a black oxide finish last?webadmin2025-07-10T07:33:10+00:00

How long does a black oxide finish last?

The lifespan of a black oxide finish varies significantly based on environmental conditions and post-treatment methods, with general ranges as follows:

Dry, indoor environments (e.g., machinery in climate-controlled facilities): When properly sealed with oil or wax, black oxide finishes typically last 5–10 years. The low moisture and minimal exposure to corrosive elements slow degradation, and periodic re-sealing (e.g., annually) can extend this further.
Moderate humidity environments (e.g., workshops, non-coastal outdoor shelters): With regular maintenance (re-sealing every 6–12 months), the finish usually endures 3–7 years. Humidity accelerates micro-corrosion, but proper sealing mitigates this.
Harsh conditions (e.g., coastal areas with salt spray, high-moisture outdoor exposure, or frequent abrasion): Lifespan shortens to 6 months–2 years without frequent re-sealing. In such settings, re-applying oil/wax every 3–6 months is critical to maintain corrosion resistance.
Unsealed finishes: Without post-treatment, even in dry environments, black oxide may degrade in 1–6 months due to oxidation and moisture absorption, losing its protective and aesthetic properties rapidly.

These ranges assume standard ferrous metals (e.g., carbon steel) and typical process parameters; high-alloy steels or specialized sealants (e.g., dry film lubricants) may extend longevity by 20–30%.

How does black oxide differ from plating or painting?webadmin2025-07-10T07:26:24+00:00

How does black oxide differ from plating or painting?

Black oxide differs fundamentally from plating or painting through its chemical transformation process and measurable performance metrics:

Coating Thickness & Dimensional Stability
Black oxide forms a 0.5–5 micron thick oxide layer directly on the metal surface, with no appreciable dimensional change. In contrast, plating (e.g., zinc, nickel) adds 3–50 micron-thick metallic layers, while paint or powder coatings typically range from 25–100 microns. For precision parts like gears or medical tools, black oxide’s near-zero dimensional impact (e.g., ±0.00002″ thickness) preserves tight tolerances, whereas plating/painting may require post-processing to maintain fit.
Corrosion Resistance (Salt Spray Testing)
Sealed black oxide provides 45–250 hours of salt spray resistance (ASTM B117), depending on post-treatment (e.g., oil, wax). Plating like zinc with chromate sealants achieves 300–1,000+ hours, but at higher cost and thickness. Paint systems may last 200–1,000 hours but require periodic reapplication and are prone to chipping. For indoor or low-moisture environments, black oxide offers a cost-effective balance.
Friction & Wear Performance
Black oxide’s smooth magnetite layer reduces friction by 15–30% compared to bare steel, with a coefficient of friction (COF) of 0.1–0.3 . Plating (e.g., nickel, chrome) typically has a COF of 0.15–0.4, while paint/coating COF varies widely (0.2–0.8) depending on surface texture. This makes black oxide ideal for sliding components like hinges or bearings, where reduced galling and wear are critical.
Adhesion & Durability
Black oxide bonds chemically to the metal substrate, achieving ASTM D3359 5B adhesion (no peeling). Plating relies on mechanical adhesion and may delaminate under stress, while paint adhesion depends on surface preparation and can chip or flake.
Cost & Process Efficiency
Compared to plating and painting, black oxide costs a lot lower and provides faster turnaound time.

In summary, black oxide offers chemically bonded corrosion resistance, minimal dimensional change, and superior tribological performance at a lower cost than plating or painting—making it ideal for precision, high-wear, or aesthetically critical applications.

Help You Turn An Idea Into A Product

Popular Plastic Injection Molding Materials