Anodizing dyes
Supplied dyes for porous anodic alumina, with named-product chemistry, physical-property bases, metal-free claim limits, and conditioned color-fastness evidence.
Tags: chemicals, anodizing, dyes, aluminum
On this page
Identity and process boundaries
Heubach’s SDS identifies Sanodal Deep Black HBL liq 102027 as an aqueous azo dye with a chromium complex. Sanodure Fast Bronze L 102260 is a powder with a copper complex. The L suffix does not identify its supplied form. Black HBL SDS Bronze SDS These dyes adsorb into porous anodic oxide before sealing. OKUNO TAC DYESTUFF
Omya lists the Sanodal, Sanodure and Sanodye families under adsorptive coloring, separately from electrolytic coloring, printing and coating. Omya process chart, p. 2
The Aluminum Anodizers Council distinguishes integral coloring, which forms and colors the oxide together, from subsequent dye adsorption. Its electrolytic-coloring description instead involves current-driven deposition from metal salts at the pore bases. A metal-complex organic dye is not interchangeable with that metal-deposition chemistry. AAC coloring FAQ
OKUNO likewise distinguishes TAC dyes from its buffers, antifoam, light-resistance improvers, and TOP SEAL products. Its nickel-acetate sealers and nickel-free sealers are separate products from the dye. A nickel-free seal does not establish the metal content of the colorant. OKUNO process description
Named products and disclosed chemistry
The following examples are references to exact names and source versions. They do not establish equivalent shades, supply forms, or formulations across manufacturers.
| Named product | Disclosed identity and supplied form | Evidence boundary |
|---|---|---|
| Sanodal Deep Black HBL liq, material 102027 | Anionic azo dyestuff/chromium complex. Blue-black aqueous solution. | Heubach USA SDS, version 5-5, revision printed as 06/05/2022. No dye CAS number or active-content assay disclosed. SDS, sections 1, 3, and 9 |
| Sanodure Fast Bronze L, material 102260 | Anionic azo dyestuff/copper complex. Brown powder. | Heubach EU SDS, version 4-3, 3 June 2022. The suffix L does not make this documented form a liquid. SDS, sections 1 and 9 |
| Alumon Brown A2RL | Dry, dark-brown powder described as a metalized azo dye. The finished shade is described as copper. | The undated Oswal Udhyog page does not name the complexing metal or a molecular identity. The shade name does not identify copper as an ingredient. Product page |
| Alumon Black LSB | Black-to-dark-grey powder described as metalized azo dyes. The finished shade is described as neutral black. | No metal identity, component proportions, or quantitative active-strength specification appears in the page. Product page |
| TAC DYESTUFF GR series | Organic dyes for anodized aluminum, described as made without heavy metals such as chromium. | OKUNO's family page supplies no individual shade identities, supply forms, CAS numbers, or assay limits. Its statement does not describe every conventional TAC dye. GR series page |
Explanatory synthesis. Azo describes a chemical class, whereas metal-complex identifies an additional coordination-chemistry feature. Neither term specifies a complete commercial formulation. No chemistry is inferred here from a trade name, color, or neighboring shade.
Sudarshan's SPA 3001 EN, 07.2025 shade card lists Fast Bronze L as granules, whereas the 2022 SDS calls it powder. The source difference remains unresolved. Shade card, p. 2 Bronze SDS, section 9
Physical properties and their measurement bases
These SDS values concern the named supplied product or a stated analytical sample. They are not working-bath settings.
| Property | Sanodal Deep Black HBL liq, USA SDS | Sanodure Fast Bronze L, EU SDS |
|---|---|---|
| Density | 1.16 g/cm³ at 20 °C and 1,013 hPa. | Density not determined. Bulk density 800 kg/m³, with no packing method stated. |
| Water solubility | Miscible at 20 °C. No numerical saturation limit stated. | Approximately 100 g/L at 20 °C. The litre denominator is not further defined as solvent volume or final solution volume. |
| pH measurement | 7–8 at 20 °C, with concentration printed as 100%. | Approximately 10 at 20 °C for a 3 g/L analytical sample. |
Sources are the complete section 9 tables, including their conditions and unavailable values. HBL SDS, pp. 4–5 Bronze SDS, pp. 7–8
Explanatory synthesis. Bulk density includes spaces between powder particles. It cannot substitute for liquid density or solid-material density. The HBL pH entry's 100% sample basis does not mean 100% active dye. Miscibility does not establish active strength, and neither SDS gives a complete solids or dye-content assay. A solubility datum also does not define a recommended bath concentration.
Ingredient disclosures and metal-free claims
The Bronze SDS lists 2-methylpentane-2,4-diol, CAS 107-41-5, at ≥1 to <10% w/w. It also lists the 3:1 mixture of chloromethylisothiazolinone and methylisothiazolinone, CAS 55965-84-9, at ≥0.0002 to <0.0015% w/w. These are supplied-mixture mass fractions, not bath concentrations. The larger percentages in the adjacent classification column are hazard-classification thresholds, not ingredient amounts. The table does not quantify the copper-complex dye. Bronze SDS, section 3, p. 2
The HBL USA SDS states that no components require disclosure under its cited OSHA standard, while identifying the product as a chromium-complex mixture. An empty disclosure list therefore does not demonstrate absence of metal or reveal a complete formulation. HBL SDS, sections 1 and 3
OKUNO explains that some conventional dyes use trivalent-chromium complexes. Its GR claim is broader than a statement restricted to hexavalent chromium, but the page supplies no analytical detection limits, total-metal assay, or shade-specific impurity results. OKUNO GR series
Explanatory synthesis. "Chromium-free," "hexavalent-chromium-free," "nickel-free," and "heavy-metal-free" have different scopes. A claim about one species does not establish absence of every metal, cobalt, or amine. None of these descriptions alone demonstrates customer approval, regulatory acceptance, or suitability for food-contact or medical use.
Color and fastness are properties of a defined finish
Powder appearance and finished-coating shade are different descriptions. Alumon Brown A2RL illustrates the distinction with a dark-brown powder and a copper-colored finish. Its light and heat ratings are qualitative, with no numerical scale or exposure method. Oswal Udhyog
For Alumon Black LSB, the supplier prints light fastness as 8+ and weather and heat fastness as excellent. The page recommends exterior use and associates its best-result claim with ANO SEAL C-200. It does not identify the light-rating scale, standard edition, exposure duration, color-change endpoint, alloy, or a test-panel seal history. These remain supplier claims with incomplete test context. They are not a demonstrated ISO rating or an outdoor-life guarantee. Alumon Black LSB
Sudarshan's shade card reports these light-fastness values. Tables and footnote 1, pp. 2, 4, and 7
| Named dye | Printed rating and oxide thickness |
|---|---|
| Sanodure Fast Bronze L | 7–8, with the general 12 µm basis. |
| Sanodal Deep Black HBL liq | >8 at 12 µm. >10 at 25 µm. |
Footnote 1 cites ISO 2135 and ISO 105B02 without editions. Its general basis is deep shades at 12 µm. Paler shades, thinner or softer layers, and lower seal quality tend to reduce fastness. Ratings need not describe the illustrated plaques, which are unsuitable for coloristic comparisons. The card supplies no exposure duration, alloy, or rating-specific seal history. Its solubility header pairs 20 °C with 60 °F, an inconsistent conversion. The SDS temperatures above retain their own basis. Shade card, pp. 7–8
Explanatory synthesis. A color name is not a measured CIELAB coordinate, spectral-reflectance curve, or color-difference tolerance. The sources above do not establish cross-brand color equivalence. A defensible numerical color comparison would also need a defined alloy, oxide coating, surface texture, seal, and optical measurement basis. AAC identifies alloy, coating thickness, texture, illumination, and observation angle as influences on appearance. AAC appearance FAQ
Light, weather, heat, and bleed resistance describe different changes. Bleeding concerns dye loss from the coating, rather than color change under light alone. The accessible product pages provide no standardized bleed rating. OKUNO identifies retained acid as one possible cause of dye bleeding and distinguishes sealing from dyeing. That does not establish a universal bleeding mechanism or a correction recipe. OKUNO process description
What the public test scopes establish
ISO's public abstract for ISO 2135:2024, edition 5, describes accelerated artificial-light testing of colored anodic oxidation coatings. It limits the method's role to production control where outdoor exposure has already established light fastness. It excludes coatings with an outdoor-established light-fastness number below 6. Exterior performance still depends on outdoor exposure comparable with service conditions. ISO 2135 public scope
The public scope of ISO 6581:2018, edition 3, describes a comparative test combining ultraviolet light and heat. ISO lists the edition as confirmed in 2024. Heat-sensitive colored coatings are outside its suitability, and dark specimens normally become hottest. A comparative result is not an absolute service-temperature limit. ISO 6581 public scope
Explanatory synthesis. A numerical supplier rating without a stated scale and method cannot be assigned to either standard. An accelerated exposure cannot be converted into years of outdoor color retention from these sources. Supplied-powder decomposition or ignition data also cannot establish the heat fastness of a dyed and sealed coating. No universal UV life, weathering life, or permissible finish temperature follows from this evidence.
Source coverage and supply limits
Reviewed 29 October 2026 PDT. The two Heubach SDS files are historical, region-specific documents printed in December 2022. They support the identities and property bases reported above, not a verified current formulation. The HBL revision date retains its printed numeric format because the document does not spell out the month.
Omya's current, undated announcement identifies it as the exclusive distributor of Sudarshan's aluminum-finishing portfolio across EMEA and Southeast Asia. It names Sanodal, Sanodure, and Sanodye. This establishes current portfolio representation, not availability of every historical shade or package in every region. Omya announcement
The OKUNO and Oswal pages are undated public product descriptions. The full relevant page text, property tables, SDS ingredient columns, and SDS section 9 conditions were reviewed. The complete nine-page Sudarshan shade card was read, including its notes and disclaimers. Its older Heubach filename does not override the printed 07.2025 identifier. Shade card
Several indexed Reliant technical PDFs were unavailable at retrieval, and some indexed Sudarshan product URLs redirected to a general finder. Cached numerical claims from those pages are not adopted here.
Coverage does not include complete proprietary formulations, current shade-specific TDS and SDS pairs, standardized heat or bleed test reports, or measured cross-brand color matches. This reference contains no dye or seal makeup, operating recipe, or customer capability. Surface-finishing processes describes the broader process distinctions.