The alloy, the base and the allergy nobody wanted to explain

Herreira Academy

Patrícia's letter

Every week someone sends me a photo of a reddened wrist with the caption: "the demi-fine jewelry caused an allergy." And every week I would have to explain the same thing that no label in the market explains: the allergy is not from the demi-fine piece. It is from the free nickel in the base. The piece itself — if well made — rarely causes a reaction. What causes it is what lies beneath the plating once the plating wears off.

I am going to explain the real mechanism in this letter, with a table and everything. Because a reseller who understands this sells differently — and defends the brand she chose to work with far better.

Is brass the villain? Not exactly

Brass — an alloy of copper and zinc — is the most commonly used base in quality demi-fine jewelry in Brazil. It has excellent surface finish, accepts plating with uniformity and is structurally stable. The problem people associate with brass is rarely about brass itself: it is about the addition of nickel as a stabilizer in cheaper alloys.

Suppliers who use high-nickel alloys achieve a lower purchase price per kilogram of raw material. The savings show up in the cost of the unfinished piece — but they disappear on the wrist of the customer who develops contact dermatitis. European Directive 94/27/EC limits nickel release to 0.5 μg/cm²/week for skin-contact items. Few Brazilian suppliers test this. Even fewer disclose it.

Herreira has used brass with a controlled alloy — very low free nickel — since 2008. Not because the market made it fashionable. Because of a technical choice I made when I was still assembling pieces alone in a forty-square-meter room.

What actually causes allergies (spoiler: free nickel)

The mechanism is straightforward: sweat is mildly acidic. When the gold plating wears away — especially on thin platings of 1 to 3 microns — the skin begins to touch the base alloy. If that alloy releases nickel ions, the immune system of sensitive individuals responds with allergic contact dermatitis: redness, itching, flaking. The reaction can take months to appear — and years to clear, because nickel hypersensitivity is irreversible.

Three variables control the risk:

1. Base alloy composition — how much free nickel is available to migrate to the skin.
2. Plating thickness — how long the base alloy stays protected from the skin. An 8-micron plating lasts 3 to 5 years of daily wear; a 2-micron plating, 3 to 8 months.
3. Individual sensitivity — roughly 10 to 15% of adult women already have established nickel hypersensitivity. For these women, any contact with free nickel triggers a reaction.

How to recognize a hypoallergenic base

A manufacturer who controls the base alloy will be able to answer specific questions. If the answer is evasive — "it is quality brass," "it is hypoallergenic" with no data — the risk of free nickel is real. Below are the five questions I have used as a supplier filter since 2010.

1. "What is the percentage composition of the base alloy?" — A serious supplier has a data sheet. The answer should include Cu, Zn and, critically, Ni content (must be below 0.05% by weight for controlled alloys).
2. "Is the alloy tested for nickel release per EN 1811?" — This is the European reference standard. Not required in Brazil, but it is the technical benchmark for premium market.
3. "What is the minimum gold plating thickness in your catalog?" — Below 3 microns, the risk of base exposure in less than one year of daily wear is high.
4. "Is there a recent laboratory certificate for this batch of alloy?" — Alloy compositions can vary between raw material batches. Batch-level certificates protect the reseller and the end consumer.
5. "Does the brand offer a formal twelve-month warranty against oxidation?" — The warranty is the most practical commitment: those who do not offer it know the piece will not last.

"The allergy is not from the demi-fine piece. It is from the free nickel that nobody wanted to pay to control. Once you know that, you stop accepting supplier excuses."

In the Herreira Academy lessons on alloys and bases, I go deep on this topic with real lab reports, a photographic comparison of accelerated oxidation in a salt-spray chamber and a supplier audit protocol you can use before placing any order. If you want to make purchasing decisions with the same confidence I had to develop over eighteen years of production, that is where it starts.

— Patrícia

Founder of Herreira Semijoias · Goiânia, since August 2008

Herreira Semijoias — Goiânia, Goiás, Brazil
Factory, wholesale and resale: +55 (62) 3091-5858
Retail: +55 (62) 98173-0039

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