Overview
ISO 2049:1996 specifies a visual method for the determination of colour of petroleum products using the ASTM colour scale (glass standard comparators). It applies to clear petroleum liquids and waxes that do not contain artificial colourants - for example, lubricating oils, heating fuels, diesel fuels and petroleum waxes. The standard defines sample preparation, instrument and lighting requirements, comparison procedure, result expression and quality (fidelity) criteria.
Key topics and requirements
- Scope limitation: applies only to products without added dyes; waxes and petroleum products that can be examined visually when clear.
- Principle: visually compare a test sample against glass colour standards under controlled daylight-type artificial illumination; select the matching standard (or the nearest darker one) on the ASTM scale.
- Sample preparation:
- Use clear, neutral glass test cells; fill to specified depth (≥50 mm).
- If cloudy, heat until turbidity disappears and assess at elevated temperature.
- For samples darker than colour 8, dilute 15 volumes sample + 85 volumes specified petroleum solvent (kerosene-type) and test the mixture.
- Apparatus and lighting:
- Use a colorimeter with two- or three-way viewing compartments and glass colour standards (see Annex A).
- Artificial daylight source: lamp temperature specified (2 750 K or 3 300 K for halogen), with a daylight filter and frosted diffuser; illuminance on diffuser of 900 lx ± 100 lx.
- Filter and source must meet spectral/transmittance criteria to emulate diffuse daylight.
- Result expression:
- Report the ASTM colour number, e.g. “colour 7.5”.
- If intermediate, prefix darker glass number with “L”, e.g. “colour L 7.5”.
- Darker than 8 reported as “colour D 8”; diluted results annotated with “Dil”.
- Fidelity (quality):
- Repeatability limit: 0.5 colour units (95% confidence).
- Reproducibility limit: 1.0 colour unit (95% confidence).
Applications and users
ISO 2049 is used for:
- Quality control in refineries, lubricant and fuel manufacturing.
- Incoming/outgoing inspection by fuel and oil suppliers.
- Independent analytical laboratories performing routine colour specification testing.
- Regulatory and specification compliance where colour is a defined property.
Keywords: ISO 2049, petroleum products, colour determination, ASTM scale, colorimeter, laboratory testing, fuel quality, lubricant testing.
Related standards
Standards referenced in ISO 2049 include:
This method provides a practical, standardized visual procedure for consistent colour reporting of petroleum products in QC and compliance workflows.
