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D6045-20 – Standard Test Method Technical Guide
🎯 Scope and Applicability
Test Method D6045-20 specifies an automatic tristimulus method for determining the color of a wide variety of clear, liquid petroleum products. This includes undyed motor and aviation gasoline, aviation turbine fuels, naphthas, kerosine, pharmaceutical white oils, diesel fuel oils, heating oils, and lubricating oils. The method is designed to report results in terms of the well-established visual scales from Test Method D156 (Saybolt Color) and Test Method D1500 (ASTM Color).
The standard explicitly excludes solid samples, products containing dye, and materials exhibiting extreme fluorescence. Additionally, cloudy samples are strictly excluded from the scope and must be filtered until clear prior to measurement. While the method could potentially be applied to petroleum waxes with appropriate sample handling, waxes were not included in the interlaboratory round robin study; therefore, the precision of this test method for waxes is currently unknown.
⚠️ Crucial Sample Requirements: The automatic tristimulus method demands a clear, transparent sample. Dyed, cloudy, or highly fluorescent specimens are outside the scope of this standard. Cloudy samples must be filtered until clear prior to analysis.
⚙️ Test Principle and Optical Configuration
The automatic tristimulus method utilizes the CIE (Commission Internationale de l’Eclairage) system for color measurement. The instrument measures the tristimulus values X, Y, and Z of a sample using a defined light source and geometric observer. The specific conditions required by the standard are outlined below.
| 🟦 Optical Parameter | 📏 Specification |
|---|---|
| Standard Illuminant | CIE Standard Illuminant C (Correlated Color Temperature of 6774 K) |
| Standard Observer | CIE 1931 Standard Colorimetric Observer (2° field of view) |
| Instrument Type | Automatic Tristimulus Colorimeter |
The instrumentation automatically calculates the color coordinates and translates them into the empirical Saybolt and ASTM color scales. The standard references several key documents for these procedures and definitions, including Terminology E284 and Practice E308 for computing object colors.
📊 Key Measured Properties and Correlation
The primary output of Test Method D6045 is an empirically derived color rating correlated to either the Saybolt or ASTM color scale. The standard has been validated to provide a one-to-one correlation for the entire range of the ASTM Color Scale (0.5 to 8.0 Dil) and for Saybolt values ranging from 0 to +30.
✅ Seamless Integration: The one-to-one correlation across the defined ranges ensures that results from the automatic tristimulus method are directly comparable to historical data generated by the manual visual methods D156 and D1500.
| 🎯 Test Method | 📈 Validated Correlation Range | ⚡ Correlation Type |
|---|---|---|
| ASTM Color (D1500) | 0.5 (lightest) to 8.0 Dil (darkest) | 1-to-1 |
| Saybolt Color (D156) | 0 to +30 | 1-to-1 |
❓ Frequently Asked Questions
🔍 What specific petroleum products are covered by the scope of D6045?
The standard covers undyed motor and aviation gasoline, aviation turbine fuels, naphthas, kerosine, pharmaceutical white oils, diesel fuel oils, heating oils, and lubricating oils. It does not apply to solid samples, dyed products, or those with extreme fluorescence.
💡 How does the automatic instrument correlate to manual visual methods?
The instrument mathematically calculates the CIE tristimulus values and converts them to the Saybolt or ASTM Color scale values. The standard confirms a one-to-one correlation between the automated method and the manual visual methods (D156 and D1500) across the specified ranges.
⚡ What is the specified light source and observer geometry for this test method?
The method specifies the use of CIE Standard Illuminant C, which represents average daylight with a correlated color temperature of 6774 K, combined with the CIE 1931 Standard Colorimetric Observer which subtends a 2° field of view.
📌 Is the precision of this test method known for petroleum waxes?
No. Petroleum waxes were not included in the round robin test program for developing this standard. While the method may apply with appropriate sample handling, the precision for waxes is currently considered unknown.