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D237-57 – Standard Test Method Technical Guide
This specification, designated ASTM D 237 – 57 (Reapproved 1997), defines the requirements for orange shellac and other lacs. It is under the jurisdiction of ASTM Committee D-1 on Paint and Related Coatings Materials and Applications.
📐 Scope and Classification
This specification covers three types of lac: Type I (Orange Shellac) under Grades A, B, C, and D; Type II (Button Lac); and Type III (Garnet Lac). Stick-lac and seed-lac are excluded from this specification.
⚙️ Physical Properties and Requirements
The material shall conform to the requirements prescribed in Table 1. Type II button lac typically occurs as circular disks about 3 in. (76 mm) in diameter and 1/8 in. (3.2 mm) in thickness. Type III garnet lac is dark garnet in color. Note that garnet lac may be manufactured in admixture with rosin or as a dewaxed lac, but such products are not covered by this specification.
| 🟦 Property | 📏 Type I Grade A | 📐 Type I Grade B | 🎯 Type I Grade C | ⚡ Type I Grade D | 🔍 Type II | 💡 Type III |
|---|---|---|---|---|---|---|
| Matter insoluble in specified hot solvents, max % | 1.00 | 1.25 | 1.50 | 3.00 | 1.00 | 0.50 |
| Iodine number, max | 15.0 | 15.0 | 15.0 | 15.0 | 15.0 | 18.0 |
| Moisture, max % | 2.0 | 2.0 | 2.0 | 2.0 | 2.0 | 2.0 |
| Wax, max % | 5.5 | 5.5 | 5.5 | 5.5 | 5.5 | 3.5 |
| Orpiment, max % | 0.03 | 0.03 | 0.03 | 0.2 | 0.03 | 0.03 |
| Matter soluble in water, max % | 0.5 | 0.5 | 0.5 | 0.5 | 0.5 | 0.5 |
| Ash, max % | 1.0 | 1.0 | 1.0 | 1.0 | 0.5 | 0.5 |
| Rosin | none | none | none | none | none | – |
💡 Note: Color, when specified, must be no darker than a mutually agreed reference sample. Type II and III have specific trade forms as pure button and garnet lac, respectively.
📊 Test Methods and Compliance
The material shall be sampled and the properties enumerated in this specification shall be determined in accordance with Test Methods D 29. This ensures consistency and reliability across all tested batches.
✅ Compliance: Adherence to the limits in Table 1 is mandatory. For type III, rosin presence is not specified, but other properties must meet the tabulated values.
❓ Frequently Asked Questions
🔍 What is the scope of ASTM D237-57?
This specification covers orange shellac and other lacs, including Type I (Grades A-D), Type II (button lac), and Type III (garnet lac). Stick-lac and seed-lac are excluded.
💡 What are the physical property requirements for Type I orange shellac?
Type I must meet limits for insoluble matter, iodine number, moisture, wax, orpiment, water-soluble matter, ash, and rosin as per Table 1. Color is agreed upon between parties.
⚡ What is the maximum iodine number for Type III garnet lac?
According to Table 1, the maximum iodine number for Type III is 18.0, compared to 15.0 for Types I and II.
📌 How are samples tested for compliance?
Sampling and testing must follow ASTM D29 Test Methods for Lac Resins, as referenced in the specification.