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D360-12 – Standard Test Method Technical Guide
📜 Scope and Classification of Shellac Varnishes
This specification, ASTM D360-12 (Reapproved 2019), defines the requirements for shellac varnish, which is a solution or “cut” of a specific dry lac resin in specially denatured alcohol. The primary solvent approved is 95% (190 proof) ethyl alcohol denatured under ATF Formula No. 1. The standard covers Orange Shellac Varnish (Grades A and B) and Bleached Lac Varnish (Regular and Refined grades). Each type can be produced in one of six body designations: Very Light, Light, Medium, Heavy, Very Heavy, or Extra Heavy. The standard emphasizes that values in inch-pound units are the standard, with SI units provided for information only.
🎨 Specifications for Color and Drying Time
Color: The color of the finished shellac varnish must not exceed a standard mutually agreed upon by the purchaser and seller, considering the nonvolatile matter content. Per the standard, the evaluation method must be one of those described in Test Methods D29.
Drying Time: Shellac varnish is required to dry hard within 1 hour. For varnishes with a body heavier than Light Body, the sample must first be thinned to the nonvolatile matter content of a Light Body varnish before the test is performed. Special conditions for this test may be established by mutual agreement between the purchaser and the seller.
📊 Body, Cut, and Nonvolatile Matter Requirements
The “body” and “cut” of the varnish are fundamentally determined by the percentage of nonvolatile matter. The following minimum requirements must be met for each type and grade:
| 🟠 Body Designation (Cut) | 📏 Orange Varnish (Grades A & B) % Min | 🧪 Bleached Varnish (Reg. & Refined) % Min |
|---|---|---|
| Very Light Body (3-lb / 1.4-kg cut) | 28.5 | 28.0 |
| Light Body (4-lb / 1.8-kg cut) | 35.0 | 34.5 |
| Medium Body (4.5-lb / 2.0-kg cut) | 37.5 | 37.0 |
| Heavy Body (5-lb / 2.3-kg cut) | 40.0 | 39.5 |
| Very Heavy Body (6-lb / 2.7-kg cut) | 44.0 | 43.5 |
| Extra Heavy Body (8-lb / 3.6-kg cut) | 51.0 | 50.5 |
💡 Understanding the “Cut”: The term “cut” refers to the number of pounds of dry lac resin added to 1 gallon (3.8 L) of solvent. The minimum nonvolatile values shown in the table inherently account for allowances of 2% maximum moisture and volatile matter plus 3% insoluble matter in orange shellac, and 6% moisture and volatile matter in bleached lac.
⚡ Testing Advisory for Drying Time: When assessing drying time for varnishes with a body greater than Light Body (e.g., Heavy or Extra Heavy), the varnish must be thinned to the nonvolatile percentage of a Light Body varnish (35.0% for Orange, 34.5% for Bleached) before commencing the 1-hour drying test.
❓ Frequently Asked Questions
🔍 What solvent is specified for making shellac varnish per D360?
The most common solvent is 95% (190 proof) ethyl alcohol, specially denatured using ATF Formula No. 1. Other specially denatured alcohols and proprietary solvents are also permitted for this purpose.
📏 What is the exact drying time requirement for shellac varnish?
The varnish must dry hard within 1 hour. It is critical to note that for heavier bodied varnishes, the sample must be thinned to a light body consistency before the test is conducted to ensure accurate evaluation.
💡 How is the “body” of a shellac varnish defined in this standard?
The “body” is strictly based on the minimum percent of nonvolatile matter. The “cut” defines the pounds of resin added per gallon of solvent. The standard specifies six distinct bodies, ranging from Very Light (3-lb cut) to Extra Heavy (8-lb cut).
📌 What types and grades of varnish are covered under ASTM D360-12?
The specification covers two major categories: Orange Shellac Varnish (Grades A and B) and Bleached Lac Varnish (Regular and Refined grades). Each of these can be ordered in any body designation.