How to specify, plate and inspect every surface finish a brass component might need — electroplating (Ni, Sn, Au, Cr, Ag, Cu), electroless nickel, chromate passivation, lacquer, polish and shot peen. Thickness classes per ASTM B689 / B545 / B488 / MIL-G-45204, Ra targets, barrel vs rack process choice, RoHS impact, and how to specify a finish cleanly on a 2D drawing.
Last reviewed: May 2026 · For: design engineers, procurement managers, QC, plating-shop coordinators
Bare brass is corrosion-resistant under most ambient conditions but it does change colour over time. Atmospheric oxidation produces a brown-then-green patina (copper carbonates and copper acetates) that is cosmetically distracting and, in regulated industries, often unacceptable. A surface finish on brass typically achieves one or more of four engineering goals:
This guide walks through the practical surface finishes Brassland applies on production lots — what each is for, what to specify on the drawing, and what to inspect at goods-in.
Electroplating is the deposition of a metallic layer from a solution of metal ions onto the brass substrate by passing direct current through an electrolyte. The brass part is the cathode; an anode of the plating metal (or an inert anode) dissolves into the bath. The deposit is a coherent metallic layer typically 1 µm to 50 µm thick.
Nickel is by far the most common plating on brass. It deposits cleanly, has excellent adhesion to brass, blocks dezincification, accepts subsequent plating layers (gold, silver, chrome), and survives most cleaning chemistries. Two industry-standard service specifications cover the great majority of brass-nickel work:
Brass-with-nickel is also the most common underplate for tin, silver and gold finishes. A 2–5 µm nickel underplate stops zinc (from the brass) diffusing through and contaminating the top coat — that diffusion is what causes "whisker" growth on bare tin-on-brass and dull-spot formation on silver-on-brass. Two practical thickness recipes Brassland runs daily:
Tin is the dominant electroplate on brass for electrical-contact applications where the part is expected to be soldered or to mate with a tinned counterpart. Tin is soft, takes solder readily, and is RoHS-compliant when deposited from a pure-tin (matt or bright) bath. Two specifications govern most work:
A critical point unique to brass: tin deposited directly onto brass tends to grow tin "whiskers" over time as zinc diffuses into the tin layer. Whiskers can short circuits in dense electronics. To prevent this, Brassland's standard recipe for brass-tin uses a nickel underplate (typically 2–4 µm Ni followed by 4–8 µm Sn). The NASA Tin Whisker Project is the open reference for understanding why this matters.
Gold is used wherever the long-term electrical contact resistance of a brass surface must not drift — RF connectors, low-current logic-level contacts, edge connectors, biomedical electrodes. Three grades cover most engineering use:
Specifications: ASTM B488, MIL-G-45204, AMS 2422. Gold on brass always requires a nickel underplate (typically 2–5 µm Ni); a flash of gold (0.05–0.25 µm) is often acceptable for low-stress contacts, while pluggable RF connectors typically specify 0.5–1.0 µm minimum on the contact surface.
Silver has the highest electrical conductivity of any element (~106% IACS), the highest thermal conductivity, and superb solderability. The trade-off is sulfide tarnish — silver darkens in atmospheres containing sulfur (rubber outgassing, urban air, packaging materials) and the dark sulfide layer increases contact resistance over years. Where the application is high-current power transmission inside an enclosed housing, silver wins decisively. Specification: ASTM B700. Typical thickness 5–25 µm.
Two distinct chrome processes on brass should not be confused:
Note the regulatory direction on chrome: Hexavalent chromium (Cr-VI) is a REACH-restricted substance. Most brass chrome plating uses trivalent chromium (Cr-III) chemistry, which is RoHS / REACH compliant and visually almost identical to Cr-VI but with a slightly cooler tone.
Copper plate (typically 2–10 µm) is occasionally deposited on brass when later operations need a uniform copper surface — e.g. before electroforming, or to bury an inscription before re-plating. Specification: ASTM B734. Rarely the final finish on a Brassland part.
Electroless nickel (EN) deposits a nickel-phosphorus alloy onto brass by chemical reduction — no external current is used. Because the deposit forms uniformly over every surface independent of current density, EN gives perfectly uniform thickness on complex geometries — internal bores, blind holes, threads, undercut features. Three specifications govern:
EN thickness on brass typically 5–50 µm. Phosphorus content controls the properties:
| P content | Crystallinity | Hardness as-plated | Hardness after bake (400°C / 1h) | Corrosion resistance | Use |
|---|---|---|---|---|---|
| Low-P (1–4%) | Crystalline | 700 HV | 900 HV | Moderate | Hardness / wear; magnetic uses |
| Mid-P (5–9%) | Mixed | 550 HV | 1000 HV | Good | General engineering, automotive |
| High-P (10–13%) | Amorphous | 500 HV | 900 HV | Excellent | Marine, chemical, food-contact |
EN is more expensive than electroplated Ni per micron, but for components with complex geometry (manifold blocks, valve bodies with deep cross-bores) it is the only way to get a uniform coat.
Brass parts that will not be plated are often dipped in a chromate-conversion solution after CNC machining to retard the formation of patina and provide a stable, faintly amber surface. Two formulations are common:
An alternative for export to regulated markets is benzotriazole (BTA) post-dip — an organic conversion coating that forms a self-assembled molecular film on the brass surface. BTA is RoHS/REACH compliant, gives 30-60 days of indoor tarnish resistance, and is invisible. Brassland uses BTA on raw-brass lots for European customers who specify "no chromate".
For polished brass that must retain its mirror finish indefinitely — architectural hardware, instruments, exhibition fittings — a clear protective lacquer is applied over the polished brass. Common formulations:
For a much harder protective layer on visible brass, Physical Vapour Deposition (PVD) zirconium nitride (ZrN) or titanium nitride (TiN) is occasionally used — these deposit a 1–4 µm ceramic layer that looks like satin brass but is dramatically harder than the underlying metal. Marine and high-traffic architectural hardware sometimes specifies this.
Achieved by progressive mechanical buffing on cloth wheels with abrasive compounds (typically a Tripoli stage then a rouge stage). Surface roughness drops below Ra 0.1 µm. Susceptible to fingerprint marks and tarnish — always lacquered after polish.
Linear scratches at controlled grit (typically 240 to 600 grit Scotch-Brite or wire-brush wheel). Produces a "directional" surface that hides handling marks. Ra typically 0.4–0.8 µm.
Loose ceramic or porcelain media plus brass parts plus water-soluble compound tumble in a vibratory bowl. Used to deburr and homogenise the surface of CNC-turned parts. Cycle 30–240 minutes depending on burr severity. Output Ra 0.4–1.6 µm with rounded edges.
Spherical steel or ceramic shot blasted at controlled velocity. Induces compressive residual stress in the surface layer that dramatically improves fatigue life — used on brass marine propeller hubs, rotating shafts, fatigue-critical parts. Specification: SAE J442 / SAE J443 for shot peening intensity (Almen strip). Ra typically rises to 3–6 µm but the underlying fatigue benefit far outweighs the cosmetic cost.
The mechanical loading of parts into the plating bath affects cost, uniformity and minimum-feature plating.
| Aspect | Barrel plating | Rack plating |
|---|---|---|
| Part loading | Loose, tumbling in a perforated barrel | Hung individually on wire racks |
| Best for | Small, robust parts: nuts, inserts, standoffs, screw plugs, set screws | Large, fragile, complex, threaded-internally or aesthetic surface parts |
| Typical part mass | under 50 g | 50 g – 10 kg |
| Cost per part | Low (high throughput, no fixturing) | 5–20× higher (manual hanging, lower throughput) |
| Thickness uniformity | ± 30% (parts in corners get less) | ± 10% (controlled current density) |
| Surface marking | Possible barrel marks on visible faces | Single rack-contact mark (often plated through) |
| Risk | Part-to-part contact during plating; not for high-cosmetic finishes | Higher per-piece cost; risk of contact-mark on visible surface |
Brassland barrel-plates the standard catalogue (nuts, inserts, standoffs) and rack-plates engineered components where dimensional precision or visible-surface quality demands it.
The achievable Ra (arithmetic mean roughness) on a brass part depends on the upstream operation plus the finish. Typical industrial targets:
| Process | Achievable Ra (µm) | Comparable ISO 1302 N-grade | Typical use |
|---|---|---|---|
| As-machined (CNC turning, sharp tool, brass) | 0.8 – 1.6 | N6 – N7 | General engineering brass |
| As-machined (Swiss CNC, high-feed precision) | 0.4 – 0.8 | N5 – N6 | Tight-tolerance precision turning |
| Polished + buffed | 0.05 – 0.2 | N3 – N4 | Mirror cosmetic finish |
| Brushed / satin | 0.4 – 0.8 | N5 – N6 | Architectural hardware |
| Vibratory finished | 0.4 – 1.6 | N5 – N7 | Deburring + cosmetic |
| Shot peened | 3.2 – 6.3 | N9 – N10 | Fatigue-critical surfaces |
| Hot forged (as-forged) | 3.2 – 12.5 | N9 – N11 | Before secondary CNC |
| Electroplated (typical Ni / Sn) | follows substrate ± 0.1 | — | Adds ~the deposit thickness, then follows underlying Ra |
A complete finish callout on a brass-component drawing should answer five questions:
A clean drawing block looks like this:
FINISH: Electroplated nickel over brass
per ASTM B689, Class 2, type 6
thickness: 5 µm min on all surfaces
except internal threads
Inspection: X-ray fluorescence (Fischerscope)
per ISO 3497 on 5 pcs per lot
NOTE: No hexavalent chromium permitted (RoHS)
Three regulatory considerations apply to finishes on brass:
The European Copper Institute publishes regularly updated guidance on RoHS-compliant plating for brass.
This guide is cross-referenced against the following publishing bodies. Open any link to verify a specific claim.
Last reviewed: June 2026. Specifications are updated periodically by their issuing bodies; for procurement-critical decisions verify against the current published edition of each cited standard. This guide is general engineering reference only and is not a substitute for the published standard.
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