ISSUE NO. V1.3 DATE 12/12/00 17
• Discoloration and spillage in the white light sample chamber
. It is important to remove any spillage immediately and clean the
chamber area.
• Dirt on the bulb diffuser plates reducing the amount of illumination to the sample
. These should be cleaned or replaced if
dirty.
Comparison of Different Instrument Versions
Users often assume that there is only one version of the Model E and Model F Tintometers; in fact, these instruments have for some
time been supplied in slightly varying formats to meet the requirements of national and international standard test methods which
specify use of the Lovibond Tintometer. In particular, BS 684 Section 1.14, ISO/FDIS 15305 and AOCS Cc 13e-92, all standard test
methods for the determination of Lovibond colour of animal and vegetable fats and oils, specify the use of the Model F (BS 684)
(previously the Model E version AF905). These instruments include racks, which are fitted with colourless glass compensating slides in
the sample field and a black sheath to prevent light entering the sides of the sample cell; they will give different readings to the standard
Tintometer versions and to automatic Lovibond instruments.
Incorrect Use of Visual Instruments
• Incorrect use of neutral racks
. The two neutral racks included with the Tintometer should be used to dull the sample so that the
brightness in sample field and the brightness in the comparison field are comparable. Many visual instrument users fail to use
neutral glasses; the result will be a lighter colour measurement to compensate for brightness in the sample field.
• Inappropriate choice of path length
. The optical path length of the cell used should be related to the colour intensity of the
sample. As a guide, it is advisable to restrict the colour intensity of the sample to less than a total of 30 - 40 Lovibond units. Using
a shorter path length cell can reduce colour intensity.
• Subjectivity of visual measurement
. Visual measurements are influenced by the discriminatory power of operators, their
interpretation of a colour match and physiological factors such as age, eye fatigue and colour vision.
Limitations and Errors Associated with Automatic Measurement
• Use with samples which are turbid or crystalline
. This will affect colour measurement since turbidity prevents light being
transmitted through the sample.
• Lack of care in sample cell cleaning and sample preparation
. Any contamination, uneven mixing or a temperature gradient
might distort the light transmitted through the sample and affect measurements.
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