A jewelry designer reported that gold-tone pieces began losing color after only one or two months, while the supplier could not clearly explain the coating thickness. The designer wanted a product that could look good through two years of normal wear.
This is not only a thickness problem. “Long-lasting gold color” must be translated into a complete production specification: substrate, surface preparation, coating system, color reference, thickness definition, test method, acceptance criteria and care conditions.
Start by defining what the thickness number means
In our stainless steel jewelry production experience, the complete PVD coating system for many 14K- and 18K-tone processes is about 0.03 μm. In some of the 24K-tone processes we use, the complete PVD coating system can be about 0.05 μm.
These are factory-process observations, not universal industry standards. Another factory may use a different layer construction, chamber process, target material, surface preparation or measurement definition. A buyer should never assume that every supplier's “0.03 μm” describes exactly the same coating system.
The purchase specification should say whether the value refers to the complete multilayer system, one color layer, or another defined layer. It should also name the measurement method and the locations to be tested.
14K, 18K and 24K describe color direction—not guaranteed durability
Factories often use 14K, 18K and 24K as commercial shade descriptions. They are not universal color standards, and they do not by themselves define coating thickness or wear life.
A 24K-tone process does not automatically guarantee a thicker coating or two years of color retention. If a particular factory uses a thicker complete coating system for its 24K tone, that is a feature of that factory's process and should be documented as such.
For color consistency, approve a physical master sample and define the surface finish. Where tighter control is needed, add L*a*b* measurements, a Delta E tolerance and agreed viewing conditions. Our separate guide explains why PVD gold color can look brassy or olive even when a thickness has been specified.
What our wear experience can—and cannot—support
With a stable process, proper surface preparation and normal care, we have observed a 0.03 μm complete system retain its color for one year or longer in normal wear, but that is not an unconditional warranty. Results vary with product shape, friction, perspiration, climate, cleaning, cosmetics, chemicals and how often the piece is worn.
Long exposure to seawater, perfume, cleaning chemicals or other aggressive substances can shorten the service life. Rings and bracelets also face different abrasion conditions from necklaces or earrings.
A two-year claim should be treated as a development and validation target, not something established by choosing a color label or one nominal thickness value.
Parameters the purchase specification should include
- Base metal grade and surface condition
- PVD process and layer construction
- Total coating thickness and tolerance
- Approved physical color master
- Surface finish: polished, brushed or textured
- Thickness measurement method and test points
- Adhesion acceptance requirement
- Wear, perspiration or corrosion test plan
- Nickel-release or RSL requirement
- Batch sampling and inspection record
- Packaging that prevents transport abrasion
- Care instructions and excluded conditions
How to verify coating thickness
A professional laboratory can measure coating thickness and issue a report. ISO 3497 describes X-ray spectrometric methods for measuring coating thickness. Before testing an ultra-thin or multilayer PVD system, confirm that the laboratory's instrument, calibration and detection capability are suitable for the specific materials and thickness range.
Thickness will not be perfectly uniform across every point of a curved jewelry piece. Flat areas, edges, recesses and complex geometry can produce different readings. For an important order, define a multi-point thickness plan, list the test locations, record the individual readings and agree in advance whether acceptance is based on minimum values, a range or an average.
Thickness alone does not prove a two-year wear life
A useful validation plan can combine several checks, selected for the product and target market:
- Visual approval: compare production samples with the approved color and finish master.
- Thickness measurement: verify the defined coating system at agreed points.
- Adhesion testing: check that the coating remains bonded to the prepared surface.
- Corrosion or artificial perspiration testing: evaluate performance under defined exposure conditions.
- Abrasion or wear testing: select a method that reflects the contact pattern of the product category.
- Nickel-release and RSL testing: test the finished item when required by the target market or brand specification.
- Controlled wear trial: compare real-use results against the care conditions and acceptance criteria.
No single accelerated test can be translated automatically into an exact number of years in consumer use. For example, ISO 9227 standardizes salt-spray test conditions but specifically does not provide a direct prediction of long-term corrosion resistance. Test results are most useful for comparing controlled samples and monitoring process consistency.
Questions to ask a supplier before ordering
- Does the stated thickness refer to the complete PVD coating system or only one layer?
- What range and tolerance can production hold?
- Which points will be measured, and will the report show each result?
- Can you reproduce the approved physical color master in bulk production?
- Which adhesion, wear, perspiration, corrosion and nickel-release tests are suitable for this item?
- How many production pieces will be sampled from each batch?
- Which wear conditions are excluded from the color-retention expectation?