Energy-Dispersive X-Ray Fluorescence (ED-XRF) spectroscopy under Standard Operating Procedure SOP-750 authenticates solid 18-karat gold (Au750) watch cases by measuring characteristic Gold L-alpha (9.71 keV) and L-beta (11.44 keV) photon emissions to ±0.05% precision while confirming 0.00% tungsten (W), nickel (Ni), and iron (Fe) across six structural test coordinates.
Key Quantitative Laboratory Takeaways
- A calibrated Fischer Fischerscope X-Ray XAN 250 excites atomic inner-shell electrons using a 50 kV micro-focus tungsten/rhodium anode tube and a Silicon Drift Detector (SDD).
- Authentic 18K horological gold must register 750.0 to 754.0 parts per thousand (75.00%–75.40%) elemental gold (Au), with the remaining 24.60%–25.00% composed exclusively of Ag, Cu, Pd, or Pt.
- Testing six distinct structural zones—including inner spring-bar bores, caseback threads, and removable bracelet link cores—defeats thick electro-wrapped shells that fool single-point surface scans.
- Every specimen released by 18K Factory Geneve is accompanied by its live 4K Fischer XRF spectral printout and Mettler-Toledo 0.01g gravimetric readout.
| Chemical Element | Atomic Number (Z) | K-Alpha / L-Alpha Line | K-Beta / L-Beta Line | Required SOP-750 Reading (18K) | Pass / Reject Criterion |
|---|---|---|---|---|---|
| Gold (Au) | Z = 79 | L-alpha: 9.713 keV | L-beta: 11.442 keV | 75.00% – 75.45% by Mass | MANDATORY PASS (>= 75.0% Au) |
| Silver (Ag) | Z = 47 | K-alpha: 22.163 keV | K-beta: 24.942 keV | 2.00% – 15.00% (Alloy Dependent) | PASS (3N Yellow / 5N Rose Balance) |
| Copper (Cu) | Z = 29 | K-alpha: 8.048 keV | K-beta: 8.905 keV | 6.50% – 21.00% (Alloy Dependent) | PASS (Structural Matrix Hardener) |
| Palladium (Pd) | Z = 46 | K-alpha: 21.177 keV | K-beta: 23.819 keV | 13.00% – 15.50% (18K White Gold) | PASS (Bleaching Noble Element) |
| Platinum (Pt) | Z = 78 | L-alpha: 9.442 keV | L-beta: 11.071 keV | 1.80% – 2.20% (Everose) / 95.0% (Pt950) | PASS (Color Lock / Pt950 Case) |
| Tungsten (W) / Iron (Fe) | Z = 74 / Z = 26 | L-alpha: 8.398 / K: 6.404 | L-beta: 9.672 / K: 7.058 | 0.00% (Zero Base Metal Tolerance) | IMMEDIATE REJECT IF > 0.05% |
How Does Energy-Dispersive XRF Measure Gold Purity Without Damaging the Watch?
Unlike traditional fire assay (cupellation) or nitric acid touchstone testing—which permanently scar a polished watch case—Energy-Dispersive X-Ray Fluorescence (ED-XRF) is 100% non-destructive. When a watch case is placed inside our Fischer XAN 250 chamber, primary X-rays eject electrons from the inner K and L orbitals of the metal atoms. As outer-shell electrons drop down to fill those vacancies, they emit secondary fluorescent X-rays whose energy (measured in kiloelectronvolts, keV) is a unique atomic fingerprint for each element in the periodic table.
Our Silicon Drift Detector (SDD) counts tens of thousands of photons per second, resolving the Gold L-alpha peak at 9.713 keV and L-beta peak at 11.442 keV to calculate exact mass percentages within ±0.05% accuracy.
Why Single-Point Surface XRF Is Insufficient Without Bore and Link-Core Scanning
Because X-ray fluorescence in high-density gold alloys has an effective attenuation depth of approximately 15 to 35 microns, pointing a handheld XRF gun solely at the flat outer surface of a thick-wrapped watch can produce a false-positive 18K reading if the outer foil exceeds 25 microns. Under 18K Factory's Standard Operating Procedure SOP-750, we eliminate this blind spot by unscrewing a removable bracelet link and scanning directly inside the internal screw bore (Coord #04) as well as the internal lug spring-bar channel (Coord #03) and inner clasp hinge (Coord #05).
Because electro-wrapping and PVD cannot coat the interior of a 1.2 mm threaded screw bore without seizing the threads, any base-metal or tungsten core is unmasked immediately.
| Scan Coordinate ID | Anatomical Watch Location | Collimator Spot Size | Acquisition Time | Target Vulnerability Checked |
|---|---|---|---|---|
| Coord #01: Bezel Flank | Upper Tachymeter / Octagonal Bezel Rim | 0.6 mm Micro-Spot | 45 Seconds | Verifies solid Au750 bezel ring homogeneity |
| Coord #02: Lug Underside | Inside St. Bernard & 750 Hallmark Cavity | 0.3 mm Micro-Spot | 45 Seconds | Confirms deep hallmark coin-strike purity |
| Coord #03: Spring-Bar Bore | Internal 1.8mm Lug Pin Drilling Channel | 0.3 mm Micro-Spot | 60 Seconds | Defeats external gold-wrapping over steel cases |
| Coord #04: Mid-Link Core | Removed Bracelet Link Cross-Section Screw Bore | 0.6 mm Micro-Spot | 60 Seconds | Exposes hidden tungsten or brass link inserts |
| Coord #05: Clasp Blade | Inner Folding Deployant Blade Hinge | 1.0 mm Standard Spot | 45 Seconds | Ensures clasp is solid 18K gold, never plated steel |
| Coord #06: Caseback Rim | Threaded Caseback Sealing Shoulder | 0.6 mm Micro-Spot | 45 Seconds | Validates monobloc caseback alloy parity |
Combining Fischer XRF Spectra With Archimedes Specific Gravity Verification
To complement six-point XRF spectroscopy, every foundry batch undergoes hydrostatic specific gravity verification (ρ = mair / (mair − mwater)) alongside complete full-watch weighing on a Mettler-Toledo analytical balance. When a watch registers both 75.04% Au across all six XRF coordinates and its exact 1:1 authentic reference mass (such as 216.5g on a Daytona 116508 or 226.4g on a Royal Oak Chronograph 26240OR), its solid Au750 metallurgy is proven beyond scientific doubt.
Explore Verified Rolex Solid 18K Gold References in Our Register
Every timepiece referenced in this monograph is available for immediate allocation with pre-shipment 4K Mettler-Toledo gram weighing, Fischer XRF Au750 spectroscopy, and 6-position Witschi Chronoscope certification. Navigate directly to the 18K FACTORY Homepage Master Register, the Rolex Solid 18K Gold Collection Hub, or the Complete 774-Watch Catalogue:
M.Sc. Analytical Materials Science (EPFL Lausanne), Certified Non-Destructive Testing (NDT Level III) Specialist.
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