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D1223-93 – Standard Test Method Technical Guide
📊 Key Measured Properties and Standards
Specular gloss is reported in gloss units (GU) based on a theoretical perfect mirror assigned a value of 384.4 GU. The practical working standard is a polished black glass surface with a refractive index of 1.540 at the Sodium D line, calibrated to the same value. This test method provides a partial measure of surface quality and shiny appearance for coated and uncoated papers.
| 🟦 Standard Type | 📐 Refractive Index | 🎯 Gloss Value |
|---|---|---|
| Ideal mirror (theoretical) | — | 384.4 GU |
| Polished black glass | 1.540 (Sodium D line) | 384.4 GU (assigned) |
⚙️ Apparatus and Geometric Configuration
The gloss meter consists of a light source, converging lens, aperture stop, suction plate, and detector enclosed in a light‑tight matte black housing. The illuminated spot on the specimen must be rectangular with dimensions controlled by the aperture. To obtain a representative value, multiple measurements covering a total area of approximately 2000 mm² are required.
| 📐 Geometric Parameter | 📏 Specification |
|---|---|
| Illuminated spot width | 0.10d ± 0.01d (for d=100 mm: 9.0–11.0 mm) |
| Illuminated spot length | 0.05 ± 0.005d × 1/cos 75° (for d=100 mm: 17.4–21.3 mm) |
| Illuminated area per spot | 156–234 mm² (for d=100 mm) |
Ten separate sheets or ten different areas on one sheet are measured and averaged to achieve the necessary total illuminated area.
📐 Specimen and Sampling Requirements
This test method is primarily intended for coated papers but is also suitable for uncoated papers. It is not recommended for cast‑coated, highly varnished, waxed papers, or high‑gloss ink films. Sampling shall follow Practice D585, and specimens must be conditioned according to Practice D685.
⚠️ Not for high‑gloss surfaces: For cast‑coated, lacquered, or waxed papers, use TAPPI T 653 (20° method) instead of this 75° method.
💡 Sampling note: Measure 10 separate sheets or 10 different areas on one sheet and average the results. This ensures a total evaluated area of approximately 2000 mm² for a representative gloss value.
❓ Frequently Asked Questions
🔍 What is the theoretical gloss standard for this method?
The theoretical standard is an ideal, completely reflecting plane mirror with an assigned gloss value of 384.4 gloss units.
💡 How should test specimens be conditioned?
Specimens must be conditioned in accordance with ASTM Practice D685, which specifies standard atmospheric conditions for paper testing.
⚡ How many measurements are needed for a representative value?
Measure 10 separate sheets or 10 different areas on one sheet and average the readings to cover a total illuminated area of about 2000 mm².
📌 Is this test method applicable to uncoated papers?
Yes, although its chief application is for coated papers, this test method may also be used for uncoated papers as stated in Section 1.2.