⛽ Color of petroleum products (ASTM scale)
In short
Visual determination of petroleum product color by comparison with glass standards on ASTM scale (0. The test is performed according to PN-EN ISO 2049:2000; Measurement scale: 0.5–8.0 ASTM (16 degrees, 0.5 step). The procedure comprises 8 steps (about 13–14 min in total); it is used for: Quality control of base and lubricating oils — degree of refining, Diesel and fuel oil color assessment, Monitoring oil degradation in service (darkening = oxidation).
At a glance
- Standard: PN-EN ISO 2049:2000
- Category: Petrochemistry
- Procedure steps: 8
- Total time of stages: 13 min–14 min
- Measurement scale: 0.5–8.0 ASTM (16 degrees, 0.5 step)
- Optical path length: 33 mm
- Resolution (visual): 0.5 ASTM units
Overview
Petroleum product color is one of the oldest and simplest quality control parameters, used in the petroleum industry for over 100 years. The ASTM color scale (corresponds to ASTM D1500 / IP 196) covers 16 degrees from 0.5 (light straw) to 8.0 (dark red/brown) with 0.5 unit step. Optical path length in cuvette is 33 mm.
Product color provides valuable information about degree of refining, purity, degradation and contamination. Freshly refined base oils have low color (0.5–2.0), while heavy oils and fuel oils — high color (6.0–8.0). Darkening of lubricating oil in service indicates oxidation, and sudden changes in fuel color may indicate contamination or batch mixing.
The visual method involves comparing sample color with colored glass standards in a comparator (petroleum colorimeter). The observer sees simultaneously the sample field and two adjacent standard fields, facilitating interpolation. The result is reported as the nearest ASTM scale degree. Products lighter than 0.5 are designated as "lighter than 0.5" (L 0.5).
In addition to the visual method, automatic colorimeters are available (e.g., Lovibond PFXi) with 0.1 ASTM unit resolution, eliminating subjectivity of human eye assessment.
Method principle
A petroleum product sample is placed in a standard cuvette with 33 mm optical path length and observed in a colorimetric comparator under illumination with a light source close to daylight (illuminant C). The sample color is compared with standard glass standards mounted on a rotating disk. The observer selects the standard whose color best matches the sample color. If the sample color is between two adjacent standards, the higher degree is assigned.
Applications
- Quality control of base and lubricating oils — degree of refining
- Diesel and fuel oil color assessment
- Monitoring oil degradation in service (darkening = oxidation)
- Refinery process control — refining, deasphalting, hydrocracking
- Contamination and batch mixing detection
- Testing of petroleum waxes and paraffins
- Commercial specifications and quality certificates
Key parameters
| Parameter | Value |
|---|---|
| Measurement scale | 0.5–8.0 ASTM (16 degrees, 0.5 step) |
| Optical path length | 33 mm |
| Resolution (visual) | 0.5 ASTM units |
| Resolution (automatic) | 0.1 ASTM units |
| Illumination | Illuminant C (close to daylight) |
| Measurement time | <1 min per sample |
Standard
- Standard number
- PN-EN ISO 2049:2000
- Title (PL)
- Przetwory naftowe — Oznaczanie barwy (skala ASTM)
- Title (EN)
- Petroleum products — Determination of colour (ASTM scale)
Step-by-step procedure
-
Sample preparation
Ensure sample is clear and free from suspensions. If cloudy, heat to max. 79°C and cool. Do not filter. Sample must be at room temperature.
-
Cuvette preparation
Wash measurement cuvette (33 mm) with toluene, then acetone. Dry. Check for scratches and dirt on optical walls.
-
Cuvette filling
Fill cuvette with sample to required level. Close with lid to prevent evaporation of volatile fractions.
-
Placement in comparator
Insert cuvette into comparator socket. Turn on illumination. Ensure sample field is evenly illuminated.
-
Comparison with standards
Rotate disk with glass standards. Compare sample color with two adjacent standards visible simultaneously in field of view.
-
Result reading
Assign sample the value of nearest standard. If color is between two standards — report higher. If lighter than 0.5 — record "L 0.5".
-
Automatic measurement (optional)
In automatic colorimeter insert cuvette, start measurement. Device will report result with 0.1 ASTM unit resolution.
-
Recording and cleaning
Record ASTM color result. Empty and wash cuvette with toluene and acetone. Dry and store.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Colorimetric comparator (visual) | Lovibond Comparator 3000 AF650, Koehler K13250 | 8 000–20 000 PLN |
| ASTM standard disks | Glass disks 0.5–8.0 ASTM, certified | 3 000–8 000 PLN / set |
| Automatic colorimeter | Lovibond PFXi-195, Koehler K13260, HunterLab ColorFlex EZ | 30 000–60 000 PLN |
| Measurement cuvettes 33 mm | Glass cuvettes with lids, optical borosilicate | 200–500 PLN/pc. |
| Illuminant C light source | Lamp in comparator or built into automatic device | included with apparatus |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Toluene | 108-88-3 | Analytical grade, for washing measurement cuvettes |
| Acetone | 67-64-1 | Analytical grade, for rinsing and drying cuvettes |
| Color calibration standards | — | Certified ASTM reference solutions for glass standard verification |
Health and safety (OHS)
- Toluene, acetone — flammable and irritating, work under fume hood
- Petroleum products — may be flammable and irritating, use nitrile gloves
- Glass standards — fragile, handle carefully
- Safety glasses and laboratory coat required
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-EN ISO 2049:2000 — “Petroleum products — Determination of colour (ASTM scale)”.
How does this method work?
A petroleum product sample is placed in a standard cuvette with 33 mm optical path length and observed in a colorimetric comparator under illumination with a light source close to daylight (illuminant C). The sample color is compared with standard glass standards mounted on a rotating disk.
What is the measuring range and accuracy?
Measurement scale: 0.5–8.0 ASTM (16 degrees, 0.5 step); Optical path length: 33 mm; Resolution (visual): 0.5 ASTM units; Resolution (automatic): 0.1 ASTM units.
How long does the test take?
The times given for the individual stages add up to approximately 13 min–14 min. The procedure comprises 8 steps.
What equipment is required?
Colorimetric comparator (visual), ASTM standard disks, Automatic colorimeter, Measurement cuvettes 33 mm, Illuminant C light source. Indicative cost of the core instrument (Colorimetric comparator (visual)): 8 000–20 000 PLN.
Where is this test used?
Quality control of base and lubricating oils — degree of refining; Diesel and fuel oil color assessment; Monitoring oil degradation in service (darkening = oxidation); Refinery process control — refining, deasphalting, hydrocracking; Contamination and batch mixing detection; Testing of petroleum waxes and paraffins; Commercial specifications and quality certificates.
What safety precautions apply?
Toluene, acetone — flammable and irritating, work under fume hood; Petroleum products — may be flammable and irritating, use nitrile gloves; Glass standards — fragile, handle carefully; Safety glasses and laboratory coat required.
Which laboratory can perform this test?
The test is performed by laboratories accredited to ISO/IEC 17025. On LabCoda you can find them by the standard number PN-EN ISO 2049.