When I explain to a new customer how gold plating works, I always start at the beginning: the process was invented in 1840 by the Henry and George Richards Elkington brothers in Birmingham, England. In nearly two centuries, the chemistry has changed very little. What changed was the equipment, the tolerance control, and the understanding of thickness effects. Knowing this process from the inside is what allows distinguishing a factory that respects engineering from one that merely dips pieces in yellow liquid.
Electrodeposition is one of the most elegant industrial technologies that exist. A piece dipped in a solution with metallic ions receives an electrical current, and that current makes metal atoms deposit on the piece's surface, one by one, forming a continuous and adherent layer. The process is deterministic: given the time, current, temperature, and solution concentration, the final thickness can be predicted with one-tenth-of-a-micron precision.
The counterintuitive thesis
Almost every buyer imagines gold plating as a simple immersion process — piece dipped in golden liquid, comes out gold. Wrong. Plating is precision electrochemistry, with six controlled variables that need to be in sync for the result to have adhesion, uniform thickness, and stable color.
When one of the six variables falls out of range, the result fails in predictable ways: peels in three months, stains in spots, darkens on contact with acidic skin. The defects are not mysterious. They are consequences of one of the six variables having drifted out of specification.
The six steps of the industrial process
1. Piece preparation
The base piece (in brass or 925 silver) needs to be clean, polished, and activated before entering the bath. Cleaning has three chemical stages: alkaline degreasing (removes handling grease), deionized water rinse (avoids ionic contamination), acid activation (opens the pores of the base alloy). If one of the three stages fails, subsequent plating loses adhesion and peels in months.
2. Intermediate plating (nickel or palladium)
The prepared piece first receives a thin (1 to 2 microns) plating of nickel or palladium. This intermediate layer creates a transition between the non-noble base (brass) and the noble layer that comes on top. Without it, gold slips: brass has a different crystal structure than gold, and direct atomic adhesion is weak.
On sensitive skin, palladium is the correct choice — it is hypoallergenic. Nickel is cheaper and technically equivalent in performance, but can cause contact dermatitis in some people. The European norm (EU Nickel Directive 94/27/EC) limits nickel release in jewelry to 0.5 micrograms per square centimeter per week. Herreira operates below this limit even in Brazil.
3. 18k gold plating solution
The gold plating solution is a mixture of complexed gold ions (generally potassium gold sulfite or potassium gold cyanide, chosen by desired pH), color additives (cobalt for intense yellow, silver for light yellow, copper for rose gold), brightener, leveler, conducting electrolyte.
Gold concentration in solution is typically 2 to 12 grams per liter, according to the desired thickness range and the factory's deposition rate. Higher concentration deposits gold faster — but also raises operational cost per batch, since gold sits as immobilized inventory in the solution.
4. Anode, cathode, and current
The piece is the cathode (negative pole). The anode (positive pole) is generally platinized titanium, which does not dissolve in the bath. Electrical current flows in direct current (DC) with density typically between 0.5 and 5 amperes per square decimeter of the piece's area. Too low density deposits matte porous gold; too high burns the surface.
The bath agitator (mechanical or air circulation) keeps the solution in motion and prevents gold ions from depleting in the immediate vicinity of the piece. Without agitation, deposition is uneven.
5. Bath time
The fundamental relation: final thickness is proportional to bath time, given constant current. For 1 micron of gold, depending on current density, typical time is 30 to 90 seconds. For 10 microns, typical time is 5 to 15 minutes. For 15 microns (Herreira on wedding bands), time is 8 to 20 minutes.
The piece needs monitoring and removal at exact time. In automated factories, time is timer-controlled; in smaller ateliers, manual stopwatch. Late removal thickens the layer beyond specification (wasted cost); early removal leaves the layer below norm (piece rejected on inspection).
6. Post-bath and protection
After the bath, the piece passes through sequential rinsing (deionized water → hot distilled water), drying in controlled oven, and finally — on premium pieces — receives a layer of transparent ceramic varnish (E-Coat) by cathodic electrodeposition. This varnish has a protective function: creates a barrier against sweat, perfume, chlorine, and extends the gold plating's useful life by up to three times.
Without E-Coat, 18k plating in urban environments suffers accelerated wear from pollution (sulfurous gases, chlorides). With E-Coat, it spans decades in preserved condition.
Batch-by-batch XRF inspection
Every factory operating within ABNT NBR 15242 needs to measure plating thickness. The standard industrial method is X-ray fluorescence (XRF): an analyzer fires an X-ray beam at the piece and measures the characteristic emission of each metallic element (nickel, gold, silver, cobalt). The result comes in seconds, with one-tenth-of-a-micron precision.
Herreira has operated with a Bruker S1 Titan since 2014. Every plating batch has a sample taken to XRF before release. If the sample falls outside the declared range, the entire batch goes back for redo. This rigor is what guarantees consistency across thousands of pieces produced monthly — and is what allows Herreira to declare 10 to 15 microns as a stable range.
Responsible environmental disposal
The plating solution contains heavy metals (nickel, cobalt) and residual cyanides or sulfites. It cannot be discharged into common sewage. Every serious factory operates with an effluent treatment system that reduces these substances to levels acceptable by CONAMA Resolution 357/2005 before disposal.
Herreira has maintained partnership since 2015 with a licensed industrial effluent treatment company in Goiânia. Every saturated bath is collected, neutralized, and disposed according to the norm. It is an additional operational cost, but it is the only defensible way to operate.
The transparency decision
When I learned the six steps, in 2008, I decided that every piece leaving Herreira would carry that engineering visibly. Not in the sense of displaying everything on the label (no space), but in the sense of being able to answer any technical question a customer asked, without dodging. In 2026, after nearly two decades, that became house policy: any customer who asks receives the complete technical sheet of the plating applied on her piece.
This policy has no significant execution cost. It has significant implementation cost, because it requires an organized factory, traced batches, operational XRF, and a team that understands what it is answering. When you buy Herreira, you are buying that structure behind. It is not poetry. It is engineering.
Next practical step
To understand the result of this engineering on a finished piece, read 18k plating in depth. To distinguish a piece that went through this process from one that did not, read how to evaluate a piece of semijewelry and the pillar premium semijewelry vs costume jewelry. The Fundamentos lesson on electrodeposition brings workshop video showing the six steps in sequence at the atelier.