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D6020-00 – Standard Test Method Technical Guide
The D6020 −00 (Reapproved 2020) standard practice provides a definitive method for calculating the combined (non-mineral) tanning agents and the degree of tannage in vegetable-tanned leather and leather containing organic retannages. It is essential for quality control and material characterization within the leather industry.
📐 Scope and Significance
This practice is designed to determine the non‑protein or non‑nitrogen containing organic matter in leather that is not extractable with water or hexane. Typical examples include vegetable tannins and acrylic lubricants. It specifically does not apply to wet blue. The practice relies on a summation approach where known extractable components and the hide substance are subtracted from the total mass to derive the combined tannin content.
⚙️ Procedure and Calculations
The procedure requires the determination of chloroform‑soluble material, water‑soluble material, insoluble ash, and hide substance using the referenced ASTM test methods. All component values must be calculated strictly on a moisture free basis (mfb).
The percentage of combined tannin (T) in the specimen is calculated using formula (1):
Combined Tannin, % = 100 – (A + B + C + D)
where A = Chloroform‑Soluble Material, B = Water‑Soluble Material, C = Insoluble Ash, and D = Hide Substance.
The Degree of Tannage is calculated using formula (2):
Degree of Tannage = (T / D) × 100
| 🟦 Component | 📏 Test Method | 🔍 Symbol (mfb) |
|---|---|---|
| Chloroform‑Soluble Material | D3495 (Hexane Extraction) | A |
| Water‑Soluble Material | D2876 | B |
| Insoluble Ash | D2875 | C |
| Hide Substance | D2868 (Kjeldahl) | D |
⚠️ User Advisory: This standard was adopted from Federal Test Standard No. 311 Method 6631 and was approved before precision and bias statements were mandated. Users are cautioned to verify reproducibility by the use of reference materials where available.
📊 Key Measured Properties and Reporting
The standard strictly defines reporting precision to ensure consistency. The combined tannin in the specimen must be reported to the nearest 0.1%. The degree of tannage must be reported to the nearest 0.5°.
| 🎯 Property | ⚡ Calculation | 📌 Reporting Precision |
|---|---|---|
| Combined Tannin (T) | T = 100 – (A + B + C + D) | Nearest 0.1% |
| Degree of Tannage | (T / D) × 100 | Nearest 0.5° |
✅ International Compliance: This international standard was developed in accordance with the principles on standardization established by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
❓ Frequently Asked Questions
🔍 What types of leather can this practice be applied to?
This practice covers vegetable‑tanned leather and leather with organic retannages. It does not apply to wet blue.
💡 What does “Combined Tannin” represent in practice?
It represents the percentage of non‑protein organic matter fixed in the leather that is insoluble in water and hexane. Examples include vegetable tannins and synthetic acrylic lubricants.
⚡ What is the correct reporting precision for the Degree of Tannage?
As per Section 6.2 of the standard, the degree of tannage in the specimen must be reported to the nearest 0.5°.
📌 Why is a moisture free basis (mfb) required for this calculation?
Calculating all components on an mfb ensures that the results are independent of the natural moisture content of the leather, providing an accurate mass balance and consistent comparison between different specimens and laboratories.