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D29-98 – Standard Test Method Technical Guide
The ASTM D29-98 standard, officially titled “Standard Test Methods for Sampling and Testing Lac Resins,” provides the definitive framework for evaluating orange shellac, button lac, garnet lac, and bleached lac. Developed under the jurisdiction of ASTM Committee D-1 on Paint and Related Coatings, Materials, and Applications, this standard establishes uniform procedures to ensure quality and consistency in the lac resin industry. Below is a detailed breakdown of the key sampling protocols and analytical test methods defined within the standard.
📐 Sampling Procedures and Requirements
Accurate sampling is critical for representative analysis. Section 3 of D29-98 provides explicit instructions for sampling orange shellac, button lac, and garnet lac. Only original, unopened containers shall be sampled. A lot is defined as not exceeding 500 bags or packages, with a maximum net weight of 75 kg per package. A random selection of 10% of the containers in the lot must be taken, with a minimum of 5 and a maximum of 25 containers sampled.
Sampling techniques vary based on the physical form of the resin. For free-flowing resins, samples are drawn from different places in the container to accumulate a total of approximately 2.7 kg. For blocked or matted resins, pieces must be chipped from each container using an axe or pick to accumulate the same total weight (2.7 kg), which is then ground to pass a No. 4 (4.75-mm) sieve conforming to ASTM E 11.
| 🟦 Parameter | 📏 Requirement (Orange Shellac, Button Lac, Garnet Lac) |
|---|---|
| Maximum Lot Size | 500 bags or packages |
| Max Net Weight per Unit | 75 kg |
| Sample Selection Rate | 10% of containers (Min 5, Max 25) |
| Total Sample Mass Required | Approximately 2.7 kg |
| Grinding Specification (Blocked Resin) | Pass No. 4 Sieve (4.75 mm) per ASTM E 11 |
⚙️ Key Analytical Tests and Procedures
The standard outlines a comprehensive suite of test methods to characterize lac resins. These include determinations of iodine value (Sections 10-10.3), purity (11-13.2), volatile matter/moisture (14-15.2), wax content (16-16.4), matter soluble in water (17-17.2), ash (18-18.2), color (19-20.4.4), acid value (21-21.4), and saponification value (23-23.4). The presence of adulterants such as orpiment is also specifically addressed (22-22.4).
⚠️ Safety Advisory: Specific hazard statements regarding the handling of reagents (e.g., n-Butyl Alcohol per D304, 2-Ethoxyethanol per D331) are provided in Note 1 of the standard. It is the user’s responsibility to establish appropriate safety, health, and regulatory practices prior to use.
Many of these tests rely on referenced ASTM standards. For instance, the iodine value determination is based on Test Method D 1959. The color of transparent liquid lac resins is assessed using the Gardner Color Scale via Test Method D 1544. The following table summarizes some of the critical references and parameters utilized in the testing phase.
| 🎯 Test Method | 📐 Section / Reference | ⚡ Key Specification |
|---|---|---|
| Moisture / Volatile Matter | 14 – 15.2 | Determined by mass loss on heating |
| Iodine Value | 10 – 10.3 / D 1959 | Measures unsaturation |
| Color (Liquids) | 19 – 19.4.3 / D 1544 | Gardner Color Scale |
| Viscosity (Liquids) | D 1545 (Reference) | Bubble Time Method |
| Reagent Water Quality | 6 / D 1193 | ASTM D 1193 Specification |
📊 Sample Preparation and Quality Assurance
Section 3.5 of D29-98 details the meticulous preparation of samples for analysis. Whether dealing with free-flowing or ground blocked resin, the entire sample must be thoroughly mixed. The standard specifically recommends the use of a mechanical mixer for combining the resin and a riffle sampler for dividing it into representative quarters. If mechanical means are unavailable, a manual cone-and-quartering method is prescribed: the sample is heaped and divided along two intersecting diameters at right angles. The opposite quarters are then combined, mixed again, and quartered to yield the final test portions. All portions must be stored in airtight containers to maintain integrity until testing.
💡 Best Practice: The use of a mechanical mixer and a riffle sampler (as recommended in Section 3.5) is highly encouraged to minimize sample segregation and ensure the test portions are truly representative of the entire lot.
❓ Frequently Asked Questions
🔍 What specific types of natural resins fall under the scope of ASTM D29-98?
This standard explicitly covers the sampling and testing of orange shellac, button lac, garnet lac, and bleached lac.
💡 What is the maximum allowable net weight per package for a lot of lac resin sampled under this standard?
The standard stipulates that no bag or package in the lot shall exceed a net weight of 75 kg.
⚡ How is a representative sample obtained from a lot of blocked or matted lac resin?
Pieces must be chipped from multiple containers using an axe or pick until a total of approximately 2.7 kg is obtained. This material must then be ground to pass a ‘No. 4’ sieve (4.75 mm openings), which must conform to Specification ASTM E 11.
📌 Which ASTM standard is referenced for determining the color of transparent lac resin liquids?
Test Method D 1544, which utilizes the Gardner Color Scale, is the referenced standard for color determination.