Iron oxide polishing rouge
Ferric oxide identity, named rouge powders and mixed compounds, particle-size terminology, and limits of composition and polishing evidence.
Tags: abrasives, polishing, iron-oxide
On this page
Identity and terminology
Ferric oxide rouge is Fe₂O₃, CAS 1309-37-1. The 2015 Formax SDS for the red cakes A-4004, A-5004 and A-40041 lists 68–75% alumina and 8–15% ferric oxide, without an explicit mass or volume basis. The ranges describe a mixed abrasive and leave the exact recipe unresolved. Formax SDS, sections 1–3 NIOSH, Rouge
Formax also calls its alumina C-3 bar 515-6110 and its alumina/chromium oxide liquid 625-21174 rouge. Use the code and formulation to identify the abrasive. Formax C-3 product table Formax B-625 brochure, liquid compounds
Terminology synthesis is that chemical identity, mineral phase, and supplied product are separate descriptions. A red color, a "jeweler's rouge" nickname, or a general polishing application does not establish Fe₂O₃ content, purity, binder, or particle-size distribution.
Iron oxides and mineral phases
The Mineralogical Society of America's Handbook of Mineralogy distinguishes these minerals. Mineral descriptions provide identity evidence, not a specification for a manufactured polishing compound.
| Mineral | Formula and structural distinction | Boundary |
|---|---|---|
| Hematite | α-Fe₂O₃, with hexagonal crystal data | One ferric oxide phase. Its colors include steel-gray and red, with a red or reddish-brown streak. Hematite, version 1 |
| Maghemite | γ-Fe₂O₃, cubic, typically with a tetragonal supercell | A different structure with the same ideal chemical formula. The handbook describes it as strongly magnetic. Maghemite, version 1 |
| Magnetite | Fe²⁺Fe³⁺₂O₄, equivalent to Fe₃O₄, cubic spinel | Contains both ferrous and ferric iron. It is a different oxide, described as black and strongly magnetic. Magnetite |
Identity synthesis is that a Fe₂O₃ assay alone does not distinguish α and γ phases. The cited commercial rouge descriptions do not report phase analysis. They therefore do not establish phase purity or permit assignment of every rouge to hematite. Natural mineral chemistry tables also describe particular specimens, not the composition of a supplied synthetic abrasive.
Powder and formulated product examples
These examples retain their producers' individual product boundaries. Their application descriptions are not interchangeable compatibility data.
| Preparation | Exact source evidence | Unresolved properties |
|---|---|---|
| Peacock Red Rouge powder | Peacock describes iron oxide rouge for block polishing and cleaning glass before silvering. Its text also describes a slurry used with its #87 cleaner. Peacock product description | No numerical grain distribution, assay, phase analysis, or working concentration appears in the description. "Very fine" is qualitative. |
| Foredom Red Rouge A-4004, A-5004, A-40041 | Foredom lists bars and a small tube. Its Red Rouge description names final polishing of gold, silver, pewter, nickel plating, and plastics. Foredom product page | The application list supplies no measured removal rate, roughness, or test conditions. |
| Formax Midget Red Rouge 515-6252, grade 75-51 | Formax lists a 4 oz bar and names precious and soft metals as applications. Formax Midget bars | Its product page supplies no numerical abrasive distribution or complete recipe. Its relative fineness language does not establish a universal abrasive ranking. |
Preparation synthesis is that a powder, a bound cake, and a liquid dispersion have different composition descriptions. A powder mixed into liquid is not thereby equivalent to a supplier's formulated paste or stabilized suspension. The reviewed evidence contains no complete Fe₂O₃ paste or stabilized-suspension specification. Formax's liquid green example above illustrates broader trade terminology, rather than an Fe₂O₃ suspension.
Foredom's page also has an unresolved package inconsistency. Its description lists A-5004 as 17 oz, while its additional-information list assigns 9.6 oz to that code. Neither value is an abrasive concentration. The disagreement prevents treating this page as an unambiguous current package-mass specification. Foredom product page.
Mixed-abrasive chemistry and percentage limits
The Formax-authored SDS hosted by Foredom identifies A-4004, A-5004, and A-40041. Its April 23, 2015 edition describes a premolded red cake. Section 3 discloses the following ranges under a percentage heading, without explicitly identifying a mass or volume basis. SDS, sections 1–3.
| Listed ingredient | Reported % range |
|---|---|
| Aluminum oxide | 68–75 |
| Stearic acid | 15–20 |
| Iron oxide, CAS 1309-37-1 | 8–15 |
| Tallow | 5–15 |
The footnote withholds exact concentrations as a trade secret. Section 9 supplies no numerical particle size or distribution. SDS, sections 3 and 9.
Composition synthesis is that this is a mixed-abrasive preparation, not pure ferric oxide. Range endpoints are not one recipe and cannot be combined into an exact composition. The table does not quantify each abrasive's contribution to cutting or finish. It also does not establish another Formax grade's formulation.
A pigment or reagent assay answers a chemistry question. It does not establish the coarse-particle population, dispersion behavior, or polishing response of an abrasive grade. The generic Fe₂O₃ identity and the named product descriptions above leave those relationships unresolved.
Particle size, concentration, and density
Particle dimensions need a defined object and measurement. An individual grain, a cluster of grains, and a crystal phase are different descriptions. A chemical formula does not provide any of their dimensions. The producer sources reviewed here do not establish primary-grain size, agglomerate size, or crystallite dimensions for the named rouges.
HORIBA explains that particle-size results can use number, volume, weight, surface-area, or intensity distributions. Laser diffraction reports volume-based results. D50 denotes a median rather than a maximum, and a single middle value does not describe distribution width. HORIBA, distribution basis and distribution points.
Measurement synthesis is that a nominal micron label cannot be silently read as D50, D90, a maximum, or a finished-surface roughness. A percentile requires its distribution basis and test method. For units, 1 µm equals 1,000 nm. This conversion adds no missing distribution or measurement definition.
Concentration likewise requires a denominator. As a hypothetical mass-balance example, 10 g of powder plus 90 g of water gives 10% powder by total mixture mass. If that powder contains 80% Fe₂O₃ by mass, the mixture contains 8 g Fe₂O₃, or 8% of its total mass. This is explanatory synthesis, not a named rouge's formulation or working recipe. Grams per litre of added water and grams per litre of final suspension describe different volume bases.
ICSC 1577 reports ferric oxide density as 5.24 g/cm³. That substance value supplies no loose or tapped powder bulk density or compound density. ILO/WHO, physical information. Synthesis is that interparticle void space, carrier, and composition remain unresolved by a substance-density value. The same value cannot determine package fill volume or abrasive concentration.
Application and safety limits
The application evidence above consists of named producer descriptions. It contains no original comparative experiment with a specified substrate, pad, pressure, speed, and finish measurement. It therefore establishes no universal polishing mechanism, finest-abrasive ranking, removal rate, scratch-free result, mirror finish, or compatibility across metals, glass compositions, and coatings. These are limits of this reference's evidence, not customer capability statements.
NIOSH identifies eye, skin, and respiratory irritation as possible effects of rouge exposure. ICSC 1577 describes airborne-particle exposure when powder disperses and possible lung effects from repeated dust inhalation. NIOSH Rouge; ILO/WHO, exposure information.
The 2015 SDS calls the supplied cake nonhazardous under the cited OSHA standard, but also discusses buffing debris and ventilation. It says environmental effects are incompletely investigated. Those statements do not establish safe process exposure or environmental harmlessness. SDS, sections 2, 8, 10, and 12.
Source coverage and versions
The sources were reviewed on October 29, 2026 PDT. NIOSH's Rouge page gives an October 30, 2019 review date. ICSC 1577 is dated October 2004. Hematite and maghemite sheets carry 2001–2005 copyright dates and version 1. The magnetite PDF has no explicit revision identifier. The mineral sheets describe minerals rather than supplied abrasive lots.
The complete seven-page Foredom-hosted SDS is dated April 23, 2015. Formax brochure B-625 states 2017. Its upload-directory date is not its edition date. The cited Peacock, Foredom, Formax, and HORIBA webpages provide no explicit technical revision identifier. Their relevant descriptions, tables, and qualifications support the bounded claims above. No lot certificate, current formulation confirmation, or controlled comparative polishing study is included.