Buhron Research & Development · Buhron, Netherlands
The polishing cloth is a product that has existed in more or less the same form for well over a century. It is also, as far as the published literature is concerned, almost entirely unstudied.
Research on polishing at the surface science level exists, but in contexts far removed from the consumer product. Chemical mechanical planarisation, the process used to flatten silicon wafers during semiconductor fabrication, has generated extensive literature on abrasive mechanics, slurry chemistry, and surface topography at the nanoscale. Museum conservation science has produced careful work on abrasive cleaning systems for silver, notably through the Getty Conservation Institute. Industrial metal finishing and optical polishing are well-characterised fields.
In August 2023, we commissioned independent surface chemistry analysis from Dr. J. Petersen at the Fraunhofer Institute for Surface Engineering and Thin Films (IST), Braunschweig — one of Europe's leading applied surface science institutes. This article documents five years of development and the full findings of that analysis.
What this independent research confirmed:
Tarnish on silver is silver sulphide (Ag₂S) — a chemical bond, not a surface deposit. Mechanical action alone cannot reliably break it.
Independent XPS analysis by Fraunhofer IST confirmed sulphide removal and reformation of the Cr₂O₃ passive layer after treatment with the Buhron solvent cloth.
The source of surface haze post-polishing is topographic, not chemical — requiring a dedicated polishing stage to reduce surface roughness (Ra) below the optical scattering threshold (~10–20 nm).
The Buhron two-step system was designed to address both problems: chemical tarnish removal in step one, topographic recovery in step two.
The cloth sold for jewellery, silverware, and watchcases is not. Despite the fact that these products make direct physical and chemical contact with the outermost nanometres of metal surfaces, and despite the fact that what happens in those nanometres determines appearance, corrosion resistance, and long-term material integrity, no independent surface science characterisation of consumer polishing cloths appears to exist in the open literature. Performance claims on such products are made without published data to support them.
This article documents what we found when we decided to look properly.
SEM micrograph of polished stainless steel substrate at 5 µm scale (15,000×, ETD detector, 10.00 kV). The surface shows directional machining marks and fine linear scratch features characteristic of the pre-treatment condition. These topographic features, spanning tens of nanometres in depth, are the primary cause of reduced specular reflectance on untreated metal surfaces.
Tarnish on silver or stainless steel is not a surface deposit in the conventional sense. It is a chemical transformation of the outermost metal layer. Silver reacts with atmospheric hydrogen sulphide to produce silver sulphide (Ag₂S), a compound that is bonded to the metal at the atomic level. On stainless steel, sulphur compounds accumulate similarly at the surface over time. The discolouration is not something sitting on top of the metal. It is the metal itself in a changed chemical state.
This distinction matters for anyone designing a tool to reverse it. A cloth that only moves contamination around the surface will not remove sulphide tarnish. Something has to break the chemical bond.
The original Buhron cloth was designed around a straightforward observation: most polishing cloths available at the time solved one problem or the other. Abrasive cloths removed tarnish but left micro-scratches. Non-abrasive cloths cleaned surfaces without damaging them but could not address genuine tarnish. We wanted a single system that did both.
Early versions combined abrasive and polishing compounds in a microfibre substrate. Under normal viewing conditions the results were consistent. Under closer examination there was a recurring finding: a proportion of treated stainless steel surfaces showed residual haze. Specular reflectance was reduced compared to the untreated surface. The tarnish was gone, but the surface looked different to the reference in a way we could not immediately explain.
The cloth itself required as much development as the polish compound. The two are not independent variables. A formulation that performs well on one substrate will behave entirely differently on another, and the substrate properties that govern polish retention, release rate, and surface contact are numerous enough that they could not be optimised sequentially. Fibre material, fibre thickness, fabric construction, weight, pile height, and impregnation conditions all interact.
We tested natural, synthetic, and semi-synthetic fibres. Natural fibres offered good compound absorption but inconsistent release and degraded faster under repeated use. Fully synthetic fibres were more durable and more uniform in their structure, but many did not retain the polish compound at the required concentration across the fibre surface. Semi-synthetic materials occupied a middle ground, but the behaviour of each candidate changed substantially depending on fibre diameter.
Fibre thickness turned out to be one of the more consequential variables. Thicker fibres produced a stiffer contact surface with higher localised pressure per fibre, which was useful for removing deeper surface defects but too aggressive for the polishing stage. Finer fibres distributed pressure more evenly across the workpiece and produced better surface finish results, but were more susceptible to loading, the accumulation of removed material in the fibre structure that reduces performance over successive uses. The correct fibre diameter was specific to the application and could not be borrowed from adjacent textile categories.
Fabric construction was tested in both woven and non-woven configurations. Woven fabrics consistently underperformed. The regular intersecting geometry of a woven structure creates pressure concentrations at the crossover points and valleys between them, where compound accumulates rather than distributing evenly. Non-woven fabrics, with their randomised fibre orientation, produced more isotropic contact across the workpiece surface and distributed the polish compound more uniformly. This was consistent across every fibre material tested. Non-woven construction became a fixed requirement early in the development process.
Within non-woven substrates, fabric weight, measured in grams per square metre, affected both the mechanical behaviour of the cloth and its compound-holding capacity. Lower GSM fabrics were too compliant, offering insufficient resistance for the abrasive stage. Higher GSM fabrics held more compound but were slower to release it under working conditions, which affected lubrication consistency. Pile height introduced a further constraint: beyond a threshold height the cloth surface degraded too quickly under repeated use, as the fibre tips that carry the compound were removed before the cloth's working life was exhausted. The acceptable range for pile height was narrow.
The impregnation process proved to be as critical as the substrate itself. The polish compound is not applied as a coating on the cloth surface. It is introduced into the fibre structure under controlled conditions, and the quantity retained must fall within a tight range. Too little compound produces insufficient lubrication during use, increasing the risk of the fibre substrate making unmediated contact with the metal surface. Too much compound releases unevenly, produces residue on the workpiece, and changes the mechanical behaviour of the cloth.
A central component of the polish formulation is the suspension of metal-derived nano-scale particles within the compound. The role of these particles is distinct from the primary abrasive: they operate at a scale below the conventional abrasive fraction and contribute to the final surface finish in the polishing stage. Their specific size distribution and composition are proprietary. Achieving a stable suspension of these particles, one that remains homogeneous through the impregnation process and does not agglomerate within the fibre structure during storage or use, required extensive formulation work.
Several thousand formulation variants were tested across the development programme. The majority failed on one criterion or another: insufficient tarnish removal, surface haze, particle agglomeration, cloth degradation, inconsistent release, or residue. The current formulation is not the result of incremental refinement from a single starting point. It is the result of a parallel search across substrate and compound variables that took years to resolve.
SEM micrograph of one of the Buhron cloth substrates at 10 µm scale. Specific particle size distribution is proprietary.
Rather than adjust the formulation based on assumption, we commissioned an independent surface chemistry analysis. In August 2023 we sent samples to the Fraunhofer Institute for Surface Engineering and Thin Films (IST) in Braunschweig, Germany, one of Europe's leading applied surface science institutes.
The analysis was conducted by Dr. J. Petersen using X-ray Photoelectron Spectroscopy (XPS), with Mg-Kα radiation at 1253 eV, a take-off angle of 45 degrees, and a measurement spot size of approximately 1 to 2 mm. XPS probes only the outermost 5 to 10 nanometres of a surface. For reference, a human hair is approximately 70,000 nm in diameter. The measurement is sensitive to the top few atomic layers only.
Two regions of the same steel sample were compared. Region A had been processed with the Buhron solvent-based slurry. Region B was an unprocessed reference area on the same sheet.
Full survey scans of both areas identified the same elements at both surfaces: carbon, oxygen, chromium and iron, with trace signals of nickel, manganese, sulphur, silicon and calcium. The contamination signals were slightly stronger in the unprocessed reference area, consistent with the slurry cleaning the surface.
Fine scans of the C, O, Cr and Fe signals were then measured to determine surface composition and bonding states.
Table 1, Surface composition in atomic percent
| Area | C (%) | O (%) | Cr (%) | Fe (%) |
|---|---|---|---|---|
| A, processed | 56.4 | 30.1 | 1.8 | 11.7 |
| B, reference | 59.9 | 28.2 | 3.0 | 8.9 |
Source: Fraunhofer IST XPS analysis, Dr. J. Petersen, 07.09.2023
What this shows: The processed surface shows lower carbon content (consistent with removal of hydrocarbon contamination) and a higher chromium-to-iron ratio, indicating emergence of the Cr₂O₃ passive protective film.
The processed surface showed lower carbon content, consistent with removal of hydrocarbon adsorbates by the slurry. It showed higher iron and lower chromium, which Fraunhofer interpreted as consistent with the abrasive step temporarily disrupting the native chromium oxide passive layer.
The most significant finding came from the oxygen fine scan. The O1s signal shows two components: one associated with metal oxides at lower binding energy, and one associated with hydroxides, organic compounds and water at higher binding energy.
Table 2, Oxygen bonding states
| Area | Metal oxide fraction | Hydroxide / organic / water |
|---|---|---|
| A, processed | 42% | 58% |
| B, reference | 32% | 68% |
Source: Fraunhofer IST XPS analysis, Dr. J. Petersen, 07.09.2023
What this shows: The 10 percentage point increase in metal oxide fraction in the processed surface confirms that the Cr₂O₃ passive layer is actively forming — the surface is more protected after treatment, not less.
The processed surface had a 10 percentage point higher metal oxide fraction in its topmost nanometres than the untreated reference. Both Cr and Fe signals showed fully oxidised character in both areas, with no detectable metallic component.
Fraunhofer's conclusion: no clear chemical cause for the surface haze could be identified. The appearance difference was likely topographic rather than chemical in origin.
This finding changed the direction of the work substantially.
Until that point, formulation effort had focused on compound chemistry: the abrasive particle composition, the solvent carrier, the surface-active components. The XPS data indicated the chemistry was performing correctly. The surface was being cleaned. The passive layer was reforming, arguably more completely than on the untreated reference. The optical difference was mechanical: the abrasive phase was leaving a surface texture that scattered light differently from the original machined finish.
This is a known phenomenon in surface finishing. Abrasive action removes material preferentially from surface peaks, which reduces deep scratches but introduces a finer, more isotropic roughness that can reduce specular reflectance. Recovering the original reflectance requires a subsequent polishing step capable of smoothing that secondary roughness below the scale at which visible light is scattered, broadly below 10 to 20 nm for specular surfaces.
The polishing stage in the existing formulation was not achieving this consistently.
To quantify the surface state before treatment, Atomic Force Microscopy (AFM) was used to map topography at nanometre resolution across a 30 by 30 micrometre scan area. The height scale was 60 nm.
The scan showed a surface with directional machining marks from the original metalworking process and a background roughness of approximately 5 to 10 nm Ra. Individual scratch features reached depths of approximately 40 nm below the mean surface plane, with widths of 1 to 2 micrometres.
A surface with Ra in the 5 to 10 nm range sits within the range of visible light scattering. The wavelength of visible light is approximately 400 to 700 nm. Topographic features at scales of 10 to 100 nm influence reflectance measurably. A mirror finish is not chemically distinct from a dull surface; it is physically flatter at this scale.
AFM height map of untreated stainless steel substrate. Background roughness approximately 5–10 nm Ra. Discrete scratch features reaching approximately 40 nm depth.
Energy Dispersive X-ray Spectroscopy (EDS) was used to compare elemental weight composition between polished and unpolished stainless steel surfaces directly.
Table 3, EDS elemental composition, weight percent
| Element | Unpolished | Polished | Change |
|---|---|---|---|
| Sulphur (S) | 0.69% | 0.32% | -0.37% |
| Oxygen (O) | not detected | 0.48% | +0.48% |
| Chromium (Cr) | 15.66% | 16.99% | +1.33% |
| Iron (Fe) | 68.55% | 70.41% | +1.86% |
| Nickel (Ni) | 11.76% | 7.96% | -3.80% |
What this shows: The sulphur reduction (0.69% → 0.32%) directly confirms sulphide tarnish removal. The emergence of oxygen and chromium increase confirms Cr₂O₃ passive film formation. The polished surface is chemically cleaner and more corrosion-resistant than the untreated reference.
Internal EDS characterisation. Substrate: austenitic stainless steel.
The sulphur reduction confirms sulphide tarnish removal. The emergence of oxygen in the polished sample, together with chromium enrichment at the surface, reflects formation of a fresh Cr₂O₃ passive film. The nickel reduction is consistent with preferential surface dissolution during abrasive treatment, a well-documented behaviour in austenitic stainless steels.
Taken together with the XPS oxygen bonding data, the EDS results show a surface that is both chemically cleaner and more completely passivated than the untreated reference. The optical haze was occurring despite this, not because of it.
EDS spectrum (Spectrum 11) of unpolished stainless steel reference surface. Powered by Tru-Q®.
Scanning Electron Microscopy (SEM) was used to examine the cloth structure at two magnification levels.
At the 50 micrometre scale, individual fibres had diameters of approximately 30 to 40 micrometres. Fibre surfaces showed a longitudinal corrugated texture. This increases contact surface area per fibre and creates micro-channels along which removed material is transported away from the workpiece during the wiping action.
SEM micrograph at 50 µm scale. Single non-woven fibre, diameter approximately 30–40 µm, showing longitudinal corrugated surface texture.
At the 10 micrometre scale, particulate matter was visible distributed across the fibre surfaces: sub-micron nodules physically fixed to the fibre matrix rather than carried in a loose paste or liquid. This controls their distribution density, contact geometry, and the pressure applied to the workpiece surface per particle. Specific particle size distribution is proprietary.
The fibre weave geometry generates contact vectors at multiple angles relative to the wiping direction. This produces more isotropic material removal than a linear abrasive tool, which generates new directional scratches parallel to the stroke.
Tarnish cannot be removed by a simple wipe. It is a chemical bond between the metal surface and sulphur. Any tool designed to reverse it has to break that bond — which requires specific chemistry, not just friction.
Scratch removal cannot happen without a controlled abrasive, but uncontrolled abrasives introduce new surface damage. The abrasive that removes tarnish and deep scratches creates sub-micrometre ridges that scatter light and make the surface look hazy.
The only way to address both problems is to separate them into two steps with different particle sizes and substrates. Step one removes the chemistry and the deeper damage. Step two recovers the surface topography to below the optical scattering threshold.
This is why most polishing cloths do half the job. They solve either the chemistry or the physics of the surface problem — not both. That is the gap the Buhron two-step system was designed to close.
The two-step architecture of the Buhron system comes directly out of this research.
Step one: sulphide removal, hydrocarbon cleaning, mechanical levelling of deeper surface defects. Step two: fine topographic recovery, passive layer stabilisation, and reduction of surface roughness below the optical scattering threshold (if starting point allows).
Following the Fraunhofer analysis, development focused on the particle size distribution and hardness of the second-stage compound and the contact mechanics of the polishing substrate. The target was a measurable reduction in post-treatment surface roughness.
Step one: abrasive action removes sulphide tarnish but transiently disrupts the Cr₂O₃ passive layer and introduces sub-micron roughness. Step two: buffing leftover polish recovers surface planarity, reduces Ra below the optical scattering threshold, and allows passive layer reformation.
The XPS analysis was commissioned to investigate a specific problem, not to validate a product. Their conclusion that no clear chemical cause for the haze was found is accurate; the subsequent topographic interpretation and the development work that followed it are our own.
The EDS and AFM measurements were conducted separately as part of the internal characterisation programme. All data tables in this article are drawn directly from those measurements without modification.
Buhron is a Dutch manufacturer of precision metal polishing cloths, developed and produced in the Netherlands.
Independent XPS analysis: Dr. J. Petersen, Fraunhofer Institute for Surface Engineering and Thin Films (IST), Braunschweig. Report dated 07.09.2023.