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SOP: Colour Matching by the Maerz and Paul Colour Dictionary Method

GIFSQ — Global Institute for Food Safety & Quality

Principle

In the visual matching of the colour of food against standard colours, the sample is compared directly with printed colour standards. The colour dictionary of Maerz and Paul is the most commonly used; it consists of 56 charts in which seven main groups of hues are presented in spectral order, each group having 8 plates, the first printed on white and the successive ones on deepening shades of grey until the colours approach black. The Maerz and Paul colours have been defined in CIE terms and may be converted to Munsell values. In place of the colour dictionary, colours reproduced on secondary standards such as painted test panels, rings, discs or plastic models may be used.

Apparatus required

  • Maerz and Paul Dictionary of Colour (56 charts), or painted test panels, rings, discs or plastic models as secondary standards
  • Mask of neutral grey having two openings, the size of each opening being equal to the size of the individual colour patch in the chart
  • Controlled illumination (illumination is of the utmost importance in colour matching; metameric colours, having different spectral curves but appearing identical to the human eye, may match under one illuminant and not under another)

Procedure

Have observers tested for normal colour vision

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Arrange controlled illumination of the sample and the chart; note that printed paper standards may deteriorate through exposure

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Place the neutral-grey mask so that one opening lies over the sample and the other over a patch of the chart

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Move the second opening over different patches of the chart until a match is achieved

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Note the colour as matched

Precautions

  • Matching is difficult when the surfaces are different (for example, matching the colour of a glossy wet surface against a matt printed chart).
  • There is a definite jump in colour between neighbouring patches of the chart, which makes matching difficult.
  • Printed paper standards may deteriorate through exposure.

References

Ranganna, S., Handbook of Analysis and Quality Control for Fruit and Vegetable Products, 2nd edition.

Maerz, A. & M.R. Paul, Dictionary of Colour, 2nd edn., McGraw-Hill, Inc., New York (1950) — cited in the book.

Southerland, F.L., Agric. Marketing, 6 (5), 4 (1961) — cited in the book.