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D4288-02 – Standard Test Method Technical Guide
📐 Pigment Classification and Types
ASTM D4288-02 (Reapproved 2019) provides the standard specification for calcium borosilicate composite pigments. The standard defines two principal types that differ in chemical composition, with Type I further subdivided into two classes based on their oil absorption characteristics. All grades consist of a complex composite of alkaline earth silicates and borates.
| 🟦 Classification | 📏 Defining Characteristics |
|---|---|
| Type I, Class A | Standard chemical composition; Lower oil absorption |
| Type I, Class B | Standard chemical composition; Higher oil absorption |
| Type II | Alternative specified chemical composition |
⚙️ Composition and Key Physical Properties
Mass color for all conforming pigments must be white. Particle size distribution is highly controlled, with the majority of particles falling within the 1 to 10 µm range. Coarse particle content and Specific Surface Diameter (SSD) are strictly limited to ensure optimal performance in paint and coatings applications.
| 🎯 Property | 🔬 Specification Limit | ⚡ Test Method |
|---|---|---|
| Coarse Particles (45 µm / No. 325 sieve) | Retained less than 0.3% | D185 |
| Maximum Specific Surface Diameter (SSD) | 2.5 µm | D1366 |
| Dominant Particle Size Range | 1 – 10 µm | D3360 / C958 |
| Mass Color | White | Visual Observation |
| Oil Absorption (Type I) | Specific level per class | D281 |
💡 Note on Tinting Strength: If tinting strength or shade is specified, it must be evaluated against a reference sample mutually agreed upon between the purchaser and the seller.
📜 Sampling and Compliance Verification
Section 4 mandates a specific sampling protocol for compliance testing. Two samples must be taken at random from different packages for each lot or production unit. For shipments exceeding 10,000 lb (5000 kg), two samples must be taken for each 10,000 lb unit. At the discretion of the purchaser, samples from the same production unit may be tested separately or blended into a composite sample. Chemical analysis is performed according to Test Methods D4487.
✅ Test Method Compliance: This standard was reapproved in 2019. Always verify you are using the latest approved versions of the referenced test methods (D185, D281, D1366, D3360, D4487) for your conformance testing program.
❓ Frequently Asked Questions
🔍 What distinguishes Type I from Type II calcium borosilicate pigments?
The two types differ primarily in their specified chemical composition, as detailed in Table 1 of the standard. Furthermore, Type I is subdivided into Class A (lower oil absorption) and Class B (higher oil absorption).
💡 What is the maximum Specific Surface Diameter (SSD) allowed?
The maximum SSD for all types under this specification is 2.5 µm, determined using the sedimentation methods outlined in Practice D1366.
⚡ How strictly is coarse particle content controlled?
Very strictly. The standard mandates that less than 0.3% of the pigment is retained on a 45-µm (No. 325) sieve when tested in accordance with Test Methods D185.
📌 What is the required sampling plan for a large shipment?
For shipments greater than 10,000 lb (5000 kg), two samples must be taken from different packages for every 10,000 lb unit of production. For shipments under this threshold, a minimum of two samples is required.