Electroplated Finishes · October 27, 2026
Gold Plating on Zinc Alloy Die Castings: Thickness, Colors and Durability
The copper-nickel-gold stack, thicknesses from flash to heavy gold, 1N-5N color grades and the factors that drive durability: a technical guide to designing zamak parts for gold plating.
Gold plating on zinc alloy is one of the most requested finishes for fashion accessories, leather goods, fragrance packaging and furniture hardware. It turns a zamak die casting into a component with a precious look, at a fraction of the cost of solid metal. The result, however, does not depend on the gold alone. Thickness, color and durability come from a multilayer system and, even before that, from the quality of the die-cast part itself. In this guide, the Micrometal editorial team walks through the plating sequence, the industry reference values and the checks worth writing into your finishing specification.
What gold plating on zamak is, and why gold never goes directly onto zinc
Gold electroplating, also called electrolytic gilding, is the electrochemical deposition of a layer of pure 24k gold or a gold alloy (Au-Co, Au-Ni, Au-Ag) from cyanide, acid or neutral baths. Its purpose can be decorative or functional: electrical conductivity and corrosion resistance.
Zinc, however, is a difficult substrate. It is highly reactive, and a noble metal deposited directly onto the casting would give poor adhesion and blistering. That is why gold plating on zamak is always built on a “stack”: a cyanide copper strike for adhesion, acid copper for leveling, bright nickel as a barrier and mechanical support, and finally the gold. This is the same principle described by the International Zinc Association in its guidelines on polishing and plating zinc die castings, and covered in ASM Handbook Vol. 5 on Surface Engineering.
A historical note: the technique was born in Italy. In 1805, at the University of Pavia, the first electrolytic gilding experiment was carried out using the newly invented voltaic pile.
A commercial caveat: a gold-plated zamak item is not gold and has no value as a precious metal. In the EU it cannot be sold as “gold”.
The complete sequence: degreasing, cyanide copper strike, acid copper, bright nickel and gold
The process, carried out by specialist plating shops, follows the same copper-nickel sequence already well established as a base for chrome and silver plating. For decorative Cu+Ni+Cr coatings on zinc, the reference standards are EN ISO 1456 (which replaced EN 12540) and ASTM B456.
Surface preparation
The casting is deburred and pre-polished, following the same logic as polishing zamak before chrome plating, and then degreased. Electrocleaning must finish in the anodic phase; acid pickling must be mild, just enough to remove the surface zinc film without attacking the casting.
Copper and nickel
The cyanide copper strike on zamak provides the anchor: without copper, the nickel would attack the zinc. Industry reference values reported on specialist technical forums (finishing.com) indicate at least 25-30 µin, roughly 0.6-0.75 µm, for the strike. The same source notes that the ASTM B252 guide recommends at least 5 µm of cyanide copper before subsequent layers: this is a guide recommendation, not a specification value, and in practice total copper (strike plus build-up copper) runs from 5-10 µm upward. Acid copper follows, leveling the surface and improving final brightness, and then bright nickel: the industry reference is at least 1.3 µm (50 µin), as a continuous layer.
Gold and protection
The sequence ends with an optional gold strike, the final deposit (24k or hard gold) and, on thin gold coatings, a clear protective lacquer.
Zamak casting → Deburring / pre-polishing → Degreasing → Electrocleaning (anodic finish) → Mild pickling → Cyanide Cu strike → Acid copper → Bright nickel → Gold plating (24k or hard gold) → Lacquer / drying → XRF thickness check
Yes → consider EN 1811 testing on the finished part and evaluate nickel-free alternatives at the design stage.
No → standard Cu-Ni-Au sequence.
Blistering and peeling almost always come down to three mistakes: insufficient cleaning, overly aggressive pickling and a copper strike that is too thin.
Thickness in microns: flash, standard gold plating and heavy gold
The gold color is clearly visible below 0.25 µm (10 µin), but at that thickness it wears off quickly on parts that are handled frequently. In short: a few tenths of a micron give you the color; thickness gives you the durability.
| Class | Thickness (µm) | Equivalent (µin) | Reference | Typical use | Indicative durability |
|---|---|---|---|---|---|
| Flash | < 0.18 | < 7 | Commercial jewelry practice | Display items | Color only, wears quickly on contact |
| Strike/flash | < 0.25 | < 10 | MIL-DTL-45204 | Adhesion layer, color effect | Low |
| Commercial gold plating | 0.25-0.5 | 10-20 | Commercial practice | Fashion accessories, costume jewelry | Medium, better with lacquer |
| Technical hard gold | ~0.8 | ~30 | Typical value over nickel | Technical components, contacts | Good wear resistance |
| Micron gold | ~1 | ~40 | Jewelry practice | Frequently handled accessories | Good |
| Heavy gold electroplate | ≥ 2.5 | ≥ 100 | Jewelry practice | Handles, hardware, heavy-wear parts | High |
Industry reference values, not normative; durability also depends on the nickel layer and the lacquer. For engineering gold, thickness classes are defined by ASTM B488 and ISO 27874, which replaces the withdrawn ISO 4523.
The choice follows the application: a display item may only need a lacquered flash, a fashion accessory calls for a few tenths of a micron, and handles and hardware move toward one micron and beyond. Because gold consumption rises in proportion to thickness, it pays to specify the minimum functional thickness only on the significant surfaces identified on the drawing.
Color and karat: 24k gold, Au-Co/Au-Ni hard gold and 1N-5N shades
Electroplated 24k pure gold has an intense yellow tone but is a soft metal: it suits decorative use, preferably with a protective lacquer. Hard gold (bright hard gold) contains 99.7-99.9% Au with small additions of cobalt and/or nickel, reaching a Knoop hardness of 120-300 and offering markedly higher wear resistance. Au-Ag and other alloys produce paler or greenish shades; cadmium-bearing formulations, restricted under REACH, are no longer an option.
To avoid disputes over color, there is a common language: ISO 8654 defines a range of gold alloy colors, from 1N (pale yellow) to 5N (red), along with a spectral reflectance measurement method that explicitly applies to coated items as well. Citing it in your specification is far more effective than a generic “yellow gold”.
Durability, wear and discoloration: the role of nickel and porosity
Copper diffuses into gold, and so does zinc from the substrate. Without a barrier, these metals eventually reach the surface and the gold turns dull and brownish. That is why nickel must always be deposited over the copper, before the gold.
According to industry reference values, the nickel underlayer serves several functions: it inhibits pore corrosion and creep corrosion, acts as a diffusion barrier and gives the gold mechanical support that improves its wear resistance. It should be at least 1.3 µm thick and, above all, continuous.
Thin gold is also porous: the pores expose the underlying layers to the environment. Porosity decreases as thickness increases and over a well-leveled nickel layer. For wear, the choice of deposit matters: at contact and handling points, hard gold over nickel performs far better than soft 24k gold. Sweat, perfumes and detergents accelerate degradation; on thin gold coatings, clear lacquer is the simplest protection.
Gold, brass or silver plating: cost, tarnishing and appearance
All zinc die casting alloys can be polished and electroplated. According to the International Zinc Association, among the common decorative finishes (chrome, nickel, brass, silver, gold), only chrome and gold are immune to tarnishing, i.e. surface oxidation. This is the strongest technical argument in favor of gold plating.
| Criterion | Gold plating | Brass plating | Silver plating |
|---|---|---|---|
| Tarnish resistance | Immune | Low | Low, tends to darken |
| Lacquer required | Only on thin coatings | Yes | Recommended |
| Relative cost | Medium-high (thickness and gold price) | Low | Medium |
| Appearance | Warm, ISO 8654 shades | Gold-like, less stable | Bright white |
| Maintenance | Minimal | Lacquer protection | Periodic cleaning |
| Typical underlayer | Cu-Ni | Cu-Ni | Cu-Ni |
| Typical applications | Luxury, fashion, fragrance | Furniture hardware, promotional items | Giftware, accessories |
Batch-to-batch color consistency is easier to specify for gold, thanks to the ISO 8654 scale. For a deeper comparison, see our guide to silver electroplating on zamak.
Designing the die casting for gold plating: ZP alloys, surfaces and defects to avoid
The quality of a gold finish starts in the foundry. The alloy is selected according to EN 12844 (castings) and EN 1774 (ingots): ZP3 (Zamak 3) offers the best platability and dimensional stability; ZP5 (Zamak 5) or ZP2 (Zamak 2) when higher hardness is needed; ZP8 for more highly stressed parts. The full comparison is in our guide to the differences between ZP3, ZP5, ZP2 and ZP8 zamak alloys.
Gold plating makes casting defects visible: subsurface porosity, cold shuts, parting lines and flash turn into blisters, pitting and stains during the plating cycle. Gates and overflows should be positioned to keep visible surfaces sound, and the same applies to ejector pin locations and rack contact points. For causes and countermeasures, see our article on
Geometry matters too: sharp edges attract more deposit, while deep cavities and recesses receive less. Generous radii and clearly marked “significant surfaces” on the drawing make thickness predictable and measurable.
Micrometal, based in Erbusco (Brescia), Italy, since 1991 and serving customers across Europe and worldwide, operates 11 hot-chamber zinc die casting units (7 presses and 4 robotic cells) from 20 to 90 t, a setup well suited to small, thin-walled parts. Our die-casting dies are designed by our technical department and built under our direct supervision. Finishes, including gold plating, are carried out by qualified plating partners, whom we coordinate on the components we die-cast.
Quality control and standards: XRF thickness, porosity and nickel release
Thickness is measured by X-ray fluorescence according to ISO 3497, a non-destructive method, or by the coulometric method according to ISO 2177. Measuring points and sampling frequency per batch should be agreed in the specification, on the significant surfaces.
Porosity is checked with the electrographic test ISO 4524-3; adhesion by visual inspection for blisters and peeling, including after aging tests.
For parts in contact with skin, REACH (Annex XVII, entry 27) sets nickel release limits, verified with the EN 1811 test after simulated wear and corrosion according to EN 12472. A thin gold layer over nickel does not guarantee compliance. Alternatives with a nickel-free underlayer, such as Cu-Sn white bronze, are options to be evaluated and verified case by case.
On traceability, Micrometal operates an ISO 9001 certified quality system, with dimensional inspection by CMM, micrometer and microscope on the components we supply.
Technical review: Marco Sega
Content produced with the assistance of artificial intelligence systems and subject to technical oversight by our editorial team. Editorial responsibility: Micrometal S.r.l.