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D332-87 – Standard Test Method Technical Guide
📐 Overview and Scope of ASTM D332-87
ASTM D332-87 (Reapproved 2020), “Standard Test Method for Relative Tinting Strength of White Pigments by Visual Observation,” defines a referee procedure for determining the relative tinting strength of white pigments. The method involves visually comparing blue-tinted pastes of a test pigment against a reference standard of precisely the same type and grade. This test is specifically for visual observation of blue tints; instrumental evaluations of black tinted samples are covered under Test Method D2745. All values stated in SI units are regarded as the standard.
⚙️ Apparatus and Test Procedure
The test requires meticulous preparation and specific equipment. The required apparatus includes a laboratory balance sensitive to 0.1 mg, a 1-mL buret graduated in 0.1-mL divisions (accurate to 0.05 mL), and a special glass hand muller. Specified amounts of the white pigment and blue tinting pigment (typically ultramarine blue per Specification D262) are dispersed together in a vehicle (usually oil) on a ground glass rubbing surface using the muller.
It is critical to recognize that results from a muller do not necessarily correlate directly with industrial dispersion processes. Nevertheless, this method offers a fast, inexpensive, and reproducible approach for routine quality control and referee assessments.
Both the test and standard pigment dispersions are treated identically. The resulting pastes are drawn down together on a panel and visually assessed for tinting strength under standardized conditions.
📊 Key Specification Data and Calculations
The following table summarizes the critical apparatus specifications required to ensure compliance with the standard.
| 🛠️ Apparatus Element | 📏 Specific Requirement |
|---|---|
| 🟦 Balance Sensitivity | 0.1 mg |
| 🎯 Buret Capacity & Accuracy | 1 mL, 0.1 mL grad., accurate to 0.05 mL |
| ⚡ Hand Muller Weight | 6.8 kg (15 lb) |
| 📐 Muller Grinding Face | 70 to 75 mm (2 3/4 to 3 in.) diameter |
| 🧪 Rubbing Surface Dimensions | At least 355 by 510 mm (14 by 20 in.) |
| 🔎 Surface Reconditioning Medium | No. 303 optical emery and turpentine |
To derive a numerical tinting strength value, the weight of the tinting pigment used in the reference standard dispersion is carefully adjusted until the lightness of the standard paste visually matches the test pigment paste. The relative tinting strength is then calculated proportionally from the different weights of tinting pigment used.
While the standard specifies oil as the vehicle and ultramarine blue as the tinting pigment, any deviation from these materials must be formally agreed upon between the involved parties (purchaser and seller).
❓ Frequently Asked Questions
🔍 What does ASTM D332-87 measure?
This standard measures the relative tinting strength of white pigments by visually comparing blue-tinted pastes of the test pigment against a reference standard of the same type and grade.
💡 Why is the muller specification strictly defined?
The strict specification for the glass hand muller (6.8 kg weight, 70–75 mm face) ensures consistent shear force and dispersion energy is applied, which is required for generating reproducible and comparable tinting strength results.
⚡ Can this test method use any vehicle or tinting pigment?
The standard specifies oil as the vehicle and ultramarine blue (per Specification D262) as the tinting pigment. The standard explicitly states that any changes to these materials must be mutually agreed upon by the purchaser and the seller.
📌 How is the numerical tinting strength rating obtained?
A numerical rating is obtained by varying the weight of the tinting