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D262-81 – Standard Test Method Technical Guide
The ASTM D262-81 (Reapproved 1999) specification defines the rigorous requirements for the manufactured inorganic pigment known as ultramarine blue. Recognized for its distinctive hue and chemical stability, this pigment is primarily intended for use in architectural paints, industrial enamels, printing inks, and lacquers. The standard provides comprehensive criteria covering the pigment’s composition, physical properties, sampling protocols, and standardized test methods to ensure a consistent, high-quality product.
🧪 Product Composition and Conformance Requirements
The pigment is produced through the calcining of a precise mixture of clays (such as kaolin), silicas, sodium salts, sulfur, and carbonaceous material. The resulting product must be a soft, dry, finely ground powder, completely free from any admixtures of color substances. The following table details the mandatory chemical and physical limits established by the standard.
| 🟦 Property | 📏 Requirement | ⚡ Test Method |
|---|---|---|
| Matter Soluble in Water (max, %) | 1.5 | ASTM D1135 |
| Moisture & Other Volatile Matter (max, %) | 4.0 | ASTM D280 (Method A) or D1208 |
| Coarse Particles (No. 325 / 45-µm sieve, max, %) | 1.0 | ASTM D185 |
| Organic Colors or Lakes | None | ASTM D1135 (Section 18) |
🟢 Important Distinction: The requirement for “Organic Colors or Lakes: None” is a defining characteristic of this standard. It ensures the pigment’s inherent lightfastness and resistance to solvents, differentiating the manufactured inorganic product from organic blue pigments.
📋 Sampling Protocols and Standard Test Procedures
Conformance testing under this standard relies on strict statistical sampling. Two random samples must be taken from different packages for each lot, batch, or day’s pack. For shipments where markings do not distinguish production units, samples must be taken from different packages in a ratio of two samples for every 5 tons (or equivalent SI unit). For shipments of less than 10,000 lb (approximately 4,500 kg), two samples are required. The purchaser may test these samples separately or, at their option, combine equal quantities from the same production unit to form a composite sample.
| 📐 Property | 🎯 Conformance Criteria |
|---|---|
| Mass Color & Character of Tint | Within mutually agreed limits of a standard accepted by purchaser and seller (ASTM D387). |
| Tinting Strength (with White Pigment) | Within mutually agreed limits of a standard accepted by purchaser and seller (ASTM D387). |
⚠️ Procedural Guidance: All mandatory tests are linked to specific ASTM methodologies. Identification, soluble matter, and the absence of organic colors are verified per ASTM D1135. Moisture content is determined via ASTM D280 (Method A) or D1208. Coarse particle fineness is measured by ASTM D185. The critical performance attributes of color and tinting strength are validated against a standard using a mechanical muller as outlined in ASTM D387.
❓ Frequently Asked Questions
🔍 What specific product categories does ASTM D262-81 cover?
This specification covers the dry pigment commercially known as ultramarine blue. It is specifically intended for use as a colorant in paints, enamels, lacquers, and similar coating products.
💡 What are the maximum allowable limits for impurities and moisture in the pigment?
Per Section 3.1 of the standard, the pigment must not exceed 1.5% matter soluble in water, 4.0% moisture and other volatile matter, and 1.0% coarse particles retained on a No. 325 sieve. The presence of organic colors or lakes is strictly prohibited.
⚡ How is the fineness of the ground powder evaluated under this standard?
Fineness is measured by the coarse particles test, which determines the total residue retained on a No. 325 (45-micrometer) sieve. The specification mandates a maximum residue of 1.0%, ensuring a consistent, soft powder suitable for high-quality finishes.
📌 Why do the color and tinting strength requirements reference “mutually agreed upon limits”?
Unlike the fixed chemical and physical limits, color and tinting strength are subjective to the target application. The standard therefore requires the buyer and seller to agree upon a physical standard reference, ensuring the final product meets the specific hue and opacity requirements of the intended use.