Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
D50-90 – Standard Test Method Technical Guide
🧪 Scope and Preparation of Samples
ASTM D50-90 (Reapproved 2023) provides a comprehensive set of test methods for the chemical analysis of yellow, orange, red, and brown pigments containing iron and manganese. The standard specifically applies to synthetic hydrated yellow iron oxide, yellow ocher, red and brown iron oxides, raw and burnt umber, raw and burnt sienna, and venetian red (Section 1.1).
Proper sample preparation is critical for accurate analysis. According to Section 4, the sample must be thoroughly mixed and any lumps reduced to a fine powder. A key requirement for extracted pigments is grinding to a fineness that passes a No. 80 (180 µm) sieve, as defined in ASTM Specification E11.
| 🟦 Pigment Category | 🔬 Iron Oxide Test | 🎯 Calcium Compounds | ⚡ Manganese Test |
|---|---|---|---|
| Yellow Ocher | Section 11-12 | Section 13-14 | — |
| Red & Brown Oxides | Section 11-12 | Section 13-14 | — |
| Raw & Burnt Umber | Section 11-12 | Section 13-14 | Section 19-20 |
| Raw & Burnt Sienna | Section 11-12 | Section 13-14 | Section 19-20 |
| Venetian Red | Section 11-12 | Section 18 (CaCO₃) | — |
🚀 Technical Tip: Always use a representative portion of the ground sample. For moisture-sensitive tests, ensure the sample is stored in a sealed container until analysis to avoid absorbing atmospheric moisture, which can affect the results for Moisture and Volatile Matter (Section 6).
📏 Referenced Analytical Methods and Procedures
The analytical procedures outlined in D50 are organized into a logical sequence for Dry Pigments (Sections 6-20) and Pigment Pastes in Oil (Sections 21-26). The standard relies on several companion ASTM standards for specific determinations.
The following table summarizes the key referenced standards and their application within D50-90.
| 📐 Standard | 📏 Purpose in D50 | ⚡ Related Section |
|---|---|---|
| ASTM C25 | Calcium Carbonate Analysis | Section 18 |
| ASTM D185 | Coarse Particles in Pigments | Sections 8, 25 |
| ASTM D280 | Moisture and Volatile Matter | Sections 6, 22 |
| ASTM D562 | Consistency (Stormer Viscometer) | Section 26 |
| ASTM D1193 | Reagent Water Specification | Section 2 |
| ASTM D1208 | Common Properties of Pigments | Sections 9, 21, 22, 23, 24 |
| ASTM E11 | Woven Wire Test Sieve Specification | Section 4 (No. 80 / 180 µm) |
⚠️ Safety Note: Per Section 1.4, this standard does not address all safety concerns. It is the responsibility of the user to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. Always review Safety Data Sheets for reagents, particularly those used in acid digestions.
🔬 Significance and Key Analytical Determinations
These test methods serve to compile, in one place, the recommended procedures for analyzing the composition of inorganic colored pigments (Section 3.1). Given their extensive use in paints, understanding the precise chemical composition of these pigments is vital for formulators and quality control laboratories.
The standard outlines critical determinations including:
- Moisture and Loss on Ignition: Assessing volatile content and thermal stability (Sections 6-7).
- Organic Coloring Matter: Detection of toners or organic extenders (Section 10).
- Total Iron Oxide: The primary colorant component in these pigments (Sections 11-12).
- Calcium Compounds: Reported as CaO, with specific methods for carbonates in Venetian Red using ASTM C25 (Sections 13-14, 18).
- Sulfates and Lead Chromate: Determining soluble sulfates and specific tests for Lead Chromate in Ochers (Sections 15-17).
- Manganese: Essential for characterizing siennas and umbers (Sections 19-20).
✅ Key Application: The results from ASTM D50 allow paint and coatings manufacturers to verify the quality, consistency, and purity of incoming pigment lots, ensuring that color performance and chemical composition meet formulation specifications.
❓ Frequently Asked Questions
🔍 What pigments does ASTM D50-90 cover?
The standard covers the chemical analysis of yellow, orange, red, and brown pigments containing iron and manganese. This includes synthetic hydrated yellow iron oxide, yellow ocher, red and brown iron oxides, raw and burnt umber, raw and burnt sienna, and venetian red (Section 1.1).
💡 How should samples be prepared for testing according to this standard?
Samples must be thoroughly mixed and lumps ground to a fine powder. Extracted pigments specifically must be ground to pass a No. 80 (180 µm) sieve, as defined in Specification E11 (Section 4). This ensures a representative and homogenous test portion.
⚡ What is the significance of the Manganese test in this standard?
The determination of Manganese is crucial for characterizing raw and burnt siennas and umbers (Sections 19-20). Manganese content is a defining characteristic of these specific pigment types and influences their color and drying properties in paints.
📌 Which units are used in the standard?
The values stated in SI units are to be regarded as the standard per Section 1.3. No other units of measurement are included in this standard, ensuring consistency across international applications.