Bag Hardware Metals and Plating: Brass, Zinc Alloy and Steel

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Bag hardware is one of three base metals — brass, zinc alloy or stainless steel — and the finish on top decides how fast it shows wear. Brass is copper alloyed with zinc at roughly two thirds copper, the most common zinc casting alloy (zamak 3) is 96% zinc and 4% aluminium, and stainless steel protects itself with at least 10.5% chromium; gold plating only earns the name vermeil at 2.5 microns.

Bag hardware is one of three base metals — brass, zinc alloy or stainless steel — and the finish on top decides how fast it shows wear. Brass is copper alloyed with zinc at roughly two thirds copper, the common zinc casting alloy zamak 3 is 96% zinc and 4% aluminium, and stainless steel protects itself with at least 10.5% chromium.

The three base metals in bag hardware

The base metal decides how a piece of hardware behaves once the surface is marked. Brass is an alloy of copper and zinc, usually with copper as the larger share, and it has been used for fittings precisely because it is workable and takes a good polish; its weakness is that zinc reacts with the minerals in salt water, which leaves the copper behind and is why marine grades are alloyed differently. Zinc alloy is the casting metal behind most complex shapes: zamak is a zinc family with a constant 4% aluminium, and zamak 3 — 96% zinc and 4% aluminium — is the grade more than 70% of North American zinc die castings are made from. Stainless steel works the other way round, protecting itself with at least 10.5% chromium that forms a passive film able to self-heal in air, and the 316L grade adds molybdenum at 2–3% to resist pitting.

What plating thickness actually means

Plating is a coating, and coatings are specified by thickness in microns — one micron is one thousandth of a millimetre. Gold is the finish where the floor is written into regulation: under 16 CFR 23.4, a product may be called vermeil only if a sterling silver base is plated with gold at least 2.5 microns thick. Above that floor, more gold means more wear before the base metal shows through, and below the recognised definitions a gold-coloured finish is a tone rather than a metal content. That distinction is where most catalog language stops being useful. As our Balenciaga City guide puts it for that house’s own pages, nobody publishing a product page states plating thickness, so “aged brass” or “light-gold” describes a look, not an alloy, and not the thickness of the coating that will wear off it.

Tarnish and oxidation: what changes colour

Tarnish is a surface reaction, not a defect in the shape of the hardware. Copper-bearing metals darken as the copper reacts with air and moisture, and brass can eventually show green verdigris where it sits against damp leather; a lacquer or plating layer slows that down until it wears through at the contact points. Stainless steel and titanium do not tarnish the same way, because the passive chromium layer re-forms instead of consuming the metal. Zinc-alloy hardware behaves differently again: the casting is soft, so once the plating is rubbed through at a buckle edge or a zip pull, the exposed alloy corrodes rather than developing a patina. Humidity and salt accelerate all three, which is why the same bag can look new in a dry climate and dull after one wet season. The metal itself is usually unchanged; it is the surface that has changed.

Nickel and skin contact

Metal that rests against skin is regulated separately from metal that does not. Under the EU restrictions that absorbed the Nickel Directive in 2009, the migration limit is 0.5 µg/cm²/week for products in direct and prolonged contact with the skin, and 0.2 µg/cm²/week for post assemblies inserted through the body. Release is measured by EN 1811, which holds the item in artificial sweat for a week before testing, and EN 12472 simulates wear and corrosion first. Roughly 10% of people in Western Europe and North America are sensitive to nickel, so this is the one hardware number worth asking about when a chain strap or a belt buckle will sit on skin for hours.

What to ask before comparing hardware

• Base metal: solid brass, stainless steel, or a zinc-alloy casting?
• Finish: electroplated, PVD, lacquered, or bare metal?
• Plating thickness: in microns, if the seller has it — and if not, treat the colour name as a colour.
• Wear points: what happens at the zip pull and the strap anchor, where plating rubs first?
• Skin contact: is there any nickel-release information for parts that sit against skin?

Two bags can carry the same gold-coloured finish for very different reasons, and only one of them will still look the same after a year of daily use. To compare shapes and tones in context, open the Bags Catalog and check the hardware close-ups; for how the metal is attached to the leather, see the bag leather, lining and hardware guide, and for the strap metals on watches, the watch strap materials guide.

Sources for the figures in this guide