Overview
ISO 15305:1998 specifies a laboratory method to determine the Lovibond colour of animal and vegetable fats and oils. The method measures the colour of light transmitted through a known optical path of a liquid fat or oil and expresses results in Lovibond units. The standard is intended for routine quality control, product specification and trade where consistent colour grading is required.
Key Topics
- Principle: Match transmitted light through the sample with glass colour standards using a Lovibond-type colorimeter; report results in Lovibond units and record the optical path length of the cell used.
- Apparatus: Recommended instruments include Lovibond Universal tintometers (Model F and Model F/C). The standard specifies suitable lighting cabinets, viewing tubes with daylight correction filters, and glass cells with standard optical path lengths.
- Glass cells: Standard path lengths are specified (examples include 1.6 mm, 3.2 mm, 6.4 mm, 12.7 mm, 25.4 mm, 76.2 mm and 133.4 mm) so readings are comparable when the correct cell is used.
- Operator requirements: Operators must have satisfactory colour vision, retested at intervals not exceeding five years. Tinted or light-sensitive spectacles should not be used during assessment.
- Sample condition: Samples must be completely liquid, clear and bright. Sample preparation is performed in accordance with ISO 661. Sampling guidance is referenced to ISO 5555 (sampling is not part of the method itself).
- Procedure highlights: Perform the test in subdued ambient light, use compensating slides and colour racks, begin matching with a 10:1 yellow-to-red ratio and introduce blue or neutral filters only as needed (not both). Tests are performed by two trained operators; a third operator is used if readings differ significantly.
- Expression of results: Report red, yellow and blue or neutral values used to obtain the match, plus the optical path length of the cell. Do not convert measurements between cell sizes.
- Precision: Annex A provides interlaboratory precision data; ISO 5725 principles are referenced for repeatability and reproducibility evaluation.
Applications
- Quality control in edible oils and fats processing (refining, bleaching, blending).
- Specification and trade to ensure consistent colour grading across suppliers and batches.
- Product development where colour is a critical attribute for consumer acceptance.
Related Standards
- ISO 661 - Preparation of test sample for animal and vegetable fats and oils.
- ISO 5555 - Sampling of animal and vegetable fats and oils (recommended sampling practice).
- ISO 5725-1/2 - Accuracy, repeatability and reproducibility guidance used for precision assessment.
For laboratories, ISO 15305:1998 provides a practical, repeatable procedure for objective colour measurement of fats and oils using Lovibond units, supporting consistent quality assessment and commercial specifications.