In one sentence: black nickel selection should start from appearance, glare suppression or photothermal function, then confirm the underlayer protection and surface durability; “black enough” alone cannot tell you whether the whole coating system is suitable.
Literature review digest · Coatings, 2024, 14(12), 1588 · This article summarizes published research; workpiece specifications must be confirmed against the substrate, coating structure and acceptance conditions.
Three key points first
- Black nickel is a family of surface systems. Different alloys, deposition methods and blackening treatments produce different compositions and microstructures and cannot share one set of performance promises.
- The black top layer and the anti-corrosion underlayer have different roles. Surface light absorption, underlayer protection and sealing must be evaluated together; blackening does not necessarily improve corrosion resistance.
- Optical parts must specify the test wavelength band. Visual blackness, reflectance, solar absorptance and thermal emittance are different metrics and must be chosen by actual use.
What this paper studies
Ewa Rudnik’s review summarizes two routes—electroplated black nickel and blackening after electroless nickel—discussing how the black color forms and applications in decoration, optics and solar thermal collection. The author summarizes bath compositions, preparation conditions and properties from different publications and did not run a single unified verification test applicable to all black nickel. View the paper
“Black nickel” is not always pure nickel. The literature covers nickel and various nickel-based alloys, whose black color may relate to oxides, sulfides, alloy phases and surface microstructure. So samples that look equally black may still differ markedly in adhesion, abrasion resistance, corrosion resistance and spectral response.
Two process routes: where is the key difference?
1. Electroplated black nickel: a black top layer formed during deposition
The electroplating route relies on applied current. Bath composition, additives, pH, current density and temperature affect color and structure. Many of the black nickel top layers discussed in the paper are thin, and some systems have brittleness or adhesion limits, so they must be paired with a nickel underlayer and substrate pretreatment. Deep holes, edges and complex contours also require attention to current distribution; whole-part uniformity cannot be inferred from flat samples alone.
2. Blackening after electroless nickel: build the coating first, then treat the surface
The typical route discussed in the paper first deposits a Ni-P alloy, then modifies the surface by oxidative blackening. The change from grey to black relates to the formation of surface oxides and a porous microstructure; this morphology affects reflection and absorption of incident light. Phosphorus content, the original coating condition and the degree of blackening jointly affect the result; final blackness cannot be decided by the “low-, mid- or high-phosphorus” label alone.
| Item | Electroplated black nickel | Blackening after electroless nickel |
|---|---|---|
| Layer formation | Black nickel-based top layer deposited with applied current | Chemically deposited Ni-P layer, followed by surface blackening |
| Factors affecting appearance | Bath composition, current distribution, temperature and deposition conditions | Ni-P layer composition, surface condition and blackening conditions |
| Protection focus | Underlayer adhesion and protection, black top layer, sealing where needed | Integrity of the original Ni-P layer, corrosion resistance and surface durability after blackening |
| Verification on complex parts | Coverage of recesses and edges, color difference and local thickness | Solution exchange in bores, blackening uniformity and cleaning residues |
This table compiles engineering evaluation hints from the paper’s content and is not a ranking under identical test conditions. Total coating thickness, the black functional top layer and the protective underlayer must be stated separately; top-layer values cannot be taken as specifications of the whole coating system.
How performance maps to actual use
Decorative appearance: watch consistency and change in service
For decorative parts, confirm not only the depth of black but also matte or gloss, allowable color difference and viewing conditions. The paper notes that some black nickel systems need an additional organic protective layer to maintain protection and color. Protective treatments also change gloss and surface function, so color samples should correspond to the complete delivered process.
Optics & photothermal: first distinguish what to absorb and what to reflect
Optical parts usually care about reflection within a specified band; solar collector surfaces usually aim to absorb solar radiation while reducing thermal radiation losses at operating temperature. For surfaces used for radiative cooling, the emittance target may be the opposite. Visible-light photos cannot give these values directly, and the spectral results in the paper must be read together with the band, measurement method and surface condition.
Corrosion & wear: verify the complete system after blackening
A porous, rough or oxidized surface structure helps certain light-absorbing effects but does not mean corrosion protection improves at the same time. The studies cited in the paper show inconsistent corrosion performance due to differing underlayer, blackening and post-treatment conditions. Heavy sliding contact may also damage the black top layer, so exposure of the underlayer and changes in reflection can become problems before the whole coating fails.
Paper source & reading notes
Author: Ewa Rudnik. Published in Coatings, December 19, 2024, 14(12), 1588. DOI: 10.3390/coatings14121588.
This page reorganizes the open-access paper into a Chinese-language digest with AUTRA’s engineering views added; it is not a sentence-by-sentence translation. The original is licensed under CC BY 4.0 per the journal’s open-access policy; the original author does not thereby endorse AUTRA products or services. Third-party images in the paper with separate copyright notices are not reproduced on this page.
Read the paper via DOI ↗ MDPI original · Journal open-access policy
English · original title & abstract
Black Nickel Coatings: From Plating Techniques to Applications.
This review compares electrodeposited black nickel with blackened electroless nickel coatings, covering colour formation, optical functions and practical limitations. The Chinese explanation separates literature findings from AUTRA’s engineering commentary.
Source: original paper ↗ · compiled: 2026-09-30
AUTRA technical commentary
Conclusion: rewrite “we want black” as specific functional requirements and accept samples in the final delivered state—only then can the right black nickel process be chosen.
The following are AUTRA’s engineering judgments and evaluation suggestions based on the literature and do not mean the company has completed the tests in the paper.
When consulting us, first clarify the part’s main task. For decorative parts, provide color and gloss samples; for anti-glare parts, state the working band, reflection requirement and key optical surfaces; if outdoor corrosion protection is also needed, add the environmental media, service temperature and corrosion acceptance conditions. These three goals can coexist, but mark the priorities so engineers can handle the trade-offs.
Writing only “black nickel, thickness X μm” on a drawing is usually not enough. Specify whether the thickness refers to the total coating or a functional layer, and state dimensional tolerances, mating surfaces and no-plating locations. The protective underlayer, black top layer and sealing layer jointly affect final performance; quotation and sampling should target the complete structure rather than comparing a blackening step in isolation.
Sample verification is suggested in two steps: first confirm coverage and appearance on the actual substrate, surface roughness and heat-treatment condition; then put the samples through expected wiping, assembly contact or environmental tests and remeasure color and function. Where sealing or protective treatment is applied, measure reflectance in the final treated state; otherwise the tested object differs from the delivered object and the conclusion is hard to use for acceptance.
For working surfaces subject to repeated sliding, frequent disassembly or friction, check in particular how long the black top layer lasts. If both wear resistance and anti-glare requirements are high, zoning of working surfaces, masking or other surface solutions can be discussed and then decided through sampling. AUTRA’s selection focus should be a verifiable combination of color, function, durability and cost, not substituting a best value from the literature for actual workpiece verification.