Almost every customer who walks into the atelier for the first time asks me the same question in different words: "Patrícia, is this real jewelry?" In eighteen years answering, I learned no one wants a technical lecture. They want an honest criterion to decide before paying. Let me try to give that criterion.
The confusion between semijewelry and costume jewelry exists because the popular market deliberately scrambled the terms. "Plated", "bathed", "aged gold", "Turkish gold" — each name hides a manufacturing choice that defines whether the piece will last three months or three decades. When you understand the structural difference, the purchase math stops being price per unit and becomes cost per year of use.
The thesis that runs against common sense
Most buyers believe the difference between semijewelry and costume jewelry is the initial shine and the price. They are wrong on both ends.
New costume jewelry shines as much or more than semijewelry, because it usually comes with a thin half-micron plating over a cheap alloy — a layer that reflects well for thirty days. The final price can even be similar in entry-level pieces, because costume jewelry margins are very high and semijewelry margins are tight.
The real difference lies in the internal architecture of the piece and in time. Premium semijewelry has three layers: a noble base (rolled brass, 925 silver, or jewelry bronze), an intermediate plating of nickel or palladium that creates adhesion, and a high-thickness layer of 18k gold that defines its useful life. Costume jewelry has one layer — when it has any. The rest is raw painted metal.
What the technical norm says
INMETRO Ordinance 395/2021 regulates the labeling of jewelry, semijewelry, plated and costume pieces in Brazil. It defines that any piece sold as "semijewelry" must have a noble metal plating (gold, silver, rhodium, palladium) over a non-noble base, with mandatory identification of the plating type and the base alloy. Costume jewelry has no such requirement: it can be zamac (a zinc alloy) with no plating at all, or with cosmetic plating of undeclared thickness.
ABNT NBR 15242 standardizes the technical terminology of the sector: it defines micron as the mandatory unit for plating thickness declaration, distinguishes "rolled" (mechanical pressure layer) from "plated" (electrolytic layer), and requires solid gold jewelry to bear a purity marking (18k, 14k, 24k) stamped on the piece.
Sellers operating within the norm communicate three pieces of information on the tag: base alloy, plating type, and thickness in microns. Sellers operating outside it omit at least one of those three. The simplest test before buying is asking the seller for those three pieces of information in writing. A serious brand answers without hesitation.
Why thickness changes everything
Plating thickness is measured in microns, which equals one thousandth of a millimeter. To understand the scale: a human hair is about 70 microns in diameter. Average commercial costume jewelry plating ranges from 0.1 to 0.5 microns — a fraction so thin it barely covers the pores of the base alloy. Average Brazilian popular semijewelry plating ranges from 1 to 3 microns. Herreira's floor sits between 10 and 15 microns on classic pieces, reaching 15 microns on wedding bands and daily-wear rings.
The difference is not linear in perception, but it is exponential in durability. Half a micron resists about 30 days of intense wear; one micron resists 60 to 90 days; three microns hold one to two years; ten microns last five to seven years; fifteen microns last over a decade in pieces not subject to constant friction. That is the leap that separates a purchase repeated each season from one that lasts a generation.
The durability test any buyer can do
There is an empirical test I apply to every piece that enters the atelier for curation, and that I recommend to any customer who wants to validate a brand before buying multiple pieces. It is called controlled friction test, and it is simple.
Take an unworn new piece. Gently rub it with a white cotton cloth on the same spot for thirty seconds. Inspect the cloth. If a yellow or red mark appears, the plating is thin and will come off in the first week. Repeat the test after 24 hours of contact with perfume applied to the back of the hand (without direct contact, but in nearby ambient air) and after a night with the ring touching moisturizing cream. Good plating does not change. Thin plating oxidizes or peels in spots.
The most precise industrial test is X-ray fluorescence (XRF), done by equipment that measures each layer's thickness in seconds. Every serious factory has one. Herreira has operated a Bruker S1 Titan XRF analyzer since 2014 — every plating batch passes inspection before being released. For the end buyer, the at-home friction test is a reasonable substitute.
The mechanism of electrodeposition in one sentence
Gold plating in semijewelry is the result of electrodeposition: the piece is dipped into a solution with gold ions in suspension and receives an electrical current that deposits metal onto its surface, atom by atom. The longer the piece stays in the bath, and the better-prepared its prior surface (polishing, degreasing, activation), the thicker and more adherent the deposited gold layer becomes.
Costume jewelry does not undergo this process, or undergoes a brief accelerated version of a few seconds that creates only a cosmetic film. That is why the piece leaves the factory looking like jewelry but with the lifespan of a disposable.
The difference also explains the cost: 18k gold quoted on international exchanges averages around US$ 70 per gram in May 2026. To plate a single piece with 10 microns of thickness, depending on size, between 0.3 and 1.2 grams of deposited gold are required. That is the raw-material floor per piece in premium semijewelry — before labor, energy, quality control. Costume jewelry priced below that floor simply has no gold in it.
The decision I made in 2008 and still keep
When I founded Herreira in August 2008, the popular market sold pieces with half-micron plating and comfortable margins. I could have followed. I chose the eight-micron floor — three to five times above what was sold on the street. The short-term math never closed well. The long-term math gave me resellers who have been with me for over fifteen years and end customers who still wear the ring bought in 2012.
It was not vision. It was fear of having to look into the eyes of a customer who came back in three months saying the piece had darkened. In eighteen years, that fear became method.
Next practical step
If you are learning to buy — or to sell — semijewelry, start with the Fundamentos lesson on 18k plating and read the deep dive into 18k plating in layers and microns. That pair of readings gives vocabulary, criteria, and confidence to talk peer to peer with any supplier.
Before buying a new piece, ask the seller: base alloy, plating type, thickness in microns. Whoever answers without hesitation is within the norm. Whoever deflects is not. It is the simplest and most honest filter that exists.