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D1517-23 – Standard Test Method Technical Guide
The ASTM D1517-23 standard provides a comprehensive lexicon for the leather industry, defining general terms as well as those specific to sampling and testing. This guide covers key definitions from the standard’s General Terms section, offering clarity for professionals involved in the specification and procurement of hides, leather, and leather products.
🐂 Leather Types and Tannage Methods
The ASTM D1517-23 standard defines the diverse landscape of leather manufacturing, from historical tannages to modern applications. Alum leather, utilizing aluminum salts, was a principal mineral tannage before chrome tanning. In contrast, bark tannage relies on vegetable tannins derived from barks and wood. The standard further distinguishes material origins, such as alligator leather (from protected aquatic species) versus alligator-grained leather (embossed calf, sheep, or cattlehide).
| 🟦 Leather Type | 📐 Primary Applications / Properties | ⚡ Tannage / Source |
|---|---|---|
| Baseball Leather | Covers of baseballs | Alum-tanned horsehide; cheaper grades use kip/sheep |
| Bag Leather | Traveling bags and suitcases | Bovine hides, heavy sealskins, goatskins |
| Apron Leather | Textile machinery (Comber/Gill Box), blacksmith aprons | Steerhide, heavily stuffed and boarded |
| Alum Leather | Historical general leather goods | Alum tannage with other agents |
🔬 Instrument Calibration and Material Characteristics
Standardized testing relies on precise instruments. The definition of the barkometer provides a direct correlation to specific gravity for tanning solutions. A specific gravity (SG) of 1.000 is equivalent to 0 degrees Barkometer (°Bk), with each subsequent degree representing a 0.001 increase in SG. The standard also defines biological and chemical agents relevant to leather quality, such as aspergillus niger (a common mold) and bactericides used to control microbial growth.
📏 Technical Note: The barkometer scale is unique to the tanning industry. Use the formula
SG = 1.000 + (°Bk × 0.001) for accurate conversion.
| 🎯 Specific Gravity | 📐 Barkometer (°Bk) |
|---|---|
| 1.000 | 0 |
| 1.005 | 5 |
| 1.010 | 10 |
| 1.015 | 15 |
| 1.020 | 20 |
🏭 Application-Specific Leathers and Cuts
The standards define specific leathers based on their end-use. Baseball leather specifications differentiate grades by source. Apron leathers encompass diverse types from soft mellow steerhide for combing machinery to firm dry leather for rub rolls. The term back is defined as a specific cut—a crop with the head trimmed off behind the horn holes. General categories like bag leather cover heavy-duty materials for travel, while upholstery leather (referred to as automobile leather) represents a distinct specification class.
⚠️ Regulatory Warning: The standard explicitly notes that the American alligator “cannot be killed legally and, therefore, is not used by the United States industry.” Only legally sourced aquatic species with a similar grain can be marketed as alligator leather.
❓ Frequently Asked Questions
🔍 What is the difference between aniline dyed leather and an aniline finish?
Aniline dyed leather is colored using transparent dyes that penetrate the leather. An aniline finish is a clear surface coating with little or no pigmentation. While often used together to create premium leather, they are distinct processes defined in the standard.
💡 How do I convert Barkometer degrees to Specific Gravity?
According to D1517-23, the conversion is linear: Specific Gravity = 1.000 + (°Bk × 0.001). For example, a solution reading 8 °Bk has a specific gravity of 1.008.
⚡ Are “alligator” and “alligator-grained leather” the same