ISO/DIS 787-1:2026(en)

ISO/TC 256

Secretariat: DIN

Date: 2026-01-27

General methods of test for pigments and extenders — Part 1: Comparison of colour of pigments

© ISO 2026

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Contents

Foreword iv

1 Scope 1

2 Normative references 1

3 Terms and definitions 1

4 Apparatus and materials 1

5 Sampling 2

6 Procedure for sample generation 2

6.1 Procedure using an automatic muller 2

6.1.1 Test portion 2

6.1.2 Preparation of pigment dispersion 2

6.2 Procedure using a hand muller or palette knife 3

6.2.1 Test portion 3

6.2.2 Preparation of pigment dispersion 3

7 Colour comparison 3

8 Test report 3

Foreword

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This document was prepared by Technical Committee ISO/TC 256, Pigments, dyestuffs and extenders, in collaboration with the European Committee for Standardization (CEN) Technical Committee CEN/TC 298, Pigments and extenders, in accordance with the Agreement on technical cooperation between ISO and CEN (Vienna Agreement).

This second edition cancels and replaces the first edition (ISO 787-1:1982), which has been technically revised.

The main changes are as follows:

— Clause 3 on terms and definitions has been added;

— in Clause 7 the colorimeter method has been added for colour measurement and colour comparison;

— the normative references have been updated.

A list of all parts in the ISO 787 series can be found on the ISO website.

Any feedback or questions on this document should be directed to the user’s national standards body. A complete listing of these bodies can be found at www.iso.org/members.html.

General methods of test for pigments and extenders — Part 1: Comparison of colour of pigments

This document specifies a general method of test for comparing the colour of a coloured pigment with that of an agreed sample. Either of the procedures described in Clause 6 and Clause 7 is acceptable but the method using an automatic muller is the reference method.

The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 150, Raw, refined and boiled linseed oil for paints and varnishes — Specifications and methods of test

ISO 3668, Paints and varnishes — Visual comparison of colour of paints

ISO 15528, Paints, varnishes and raw materials for paints and varnishes — Sampling

ISO 18314‑1, Analytical colorimetry — Part 1: Practical colour measurement

ISO 18314‑5, Analytical colorimetry — Part 5: Procedure for colorimetric determination of colour differences of object colours according to equidistant colour spaces

ISO 18451‑1, Pigments, dyestuffs and extenders — Terminology — Part 1: General terms

ISO/CIE 11664‑4, Colorimetry — Part 4: CIE 1976 L*a*b* colour space

ISO/CIE 11664‑6, Colorimetry — Part 6: CIEDE2000 colour-difference formula

For the purposes of this document, the terms and definitions given in ISO 18451-1 apply.

ISO and IEC maintain terminology databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https://www.iso.org/obp

— IEC Electropedia: available at https://www.electropedia.org/

Use standard laboratory apparatus, together with the following.

4.1 Palette knife, with a tapered steel blade of approximate dimensions 140 mm to 150 mm long, 20 mm to 25 mm wide at its widest point and not less than 12,5 mm wide at its narrowest point, or a palette knife of suitable plastics material.

4.2 Substrate, minimum area 150 mm × 50 mm. Choose a substrate according to the binder used and the method of colour comparison. If a glass panel is used, it shall be clear and colourless.

4.3 Burette, with a delivery such that 1 ml of the binder contains about 35 drops.

4.4 Muller, either of the following may be used:

4.4.1 Automatic muller, with ground glass plates, preferably water cooled, of diameter 180 mm to 250 mm, to which a variable but known force of up to about 1 kN may be applied. The driven glass plate shall have a rotational frequency of between 70 min⁻¹ and 120 min⁻¹, and the apparatus should have an arrangement for pre-setting the number of revolutions in multiples of 25.

If the automatic muller does not have water-cooled plates, care shall be taken that temperature variations do not occur during the grinding operation.

4.4.2 Hand muller, with a diameter of 70 mm to 75 mm.

4.5 Plate, of ground glass or marble, for use when the automatic muller (4.4.1) is not available.

4.6 Binder. The binder used shall be agreed between the interested parties. If no binder is specified or agreed, linseed oil, complying with the requirements of the refined grade specified in ISO 150, shall be used.

Take a representative sample of the pigment to be tested in accordance with ISO 15528.

Take a quantity of pigment for the test such that, when mixed with a sufficient quantity of the binder to obtain the dispersion, the resulting paste extends almost to the edges of the plates of the muller. Weigh the test portion to the nearest 1 mg.

Transfer the test portion (6.1.1) to the clean lower plate of the automatic muller (4.4.1). Run a number of drops of the binder (4.6) from the burette (4.3) on to the blade of the palette knife (4.1) and, using the blade, mix the binder and pigment. Add more drops of binder as necessary to produce a paste with a suitable consistency for milling.

When the pigment has become uniformly wetted, spread the paste in a band approximately 50 mm wide about half-way between the centre and rim of the lower plate and clean the palette knife by drawing it across the upper plate. Close the muller plates, apply a force of about 1 kN and grind the paste in stages of 50 revolutions for each stage, picking up the paste with the palette knife and returning it to the 50 mm wide band after each stage.

The applied force and the number of stages depend on the pigment tested and should be the same for the pigment under test and the agreed sample.

When the grinding has been completed, add a further few drops of the binder to obtain a suitable consistency, close the muller plates and grind the paste for a further 25 revolutions. Remove the paste from the plate and store it.

Take a similar amount of the agreed sample of pigment and prepare a paste in the same way at a consistency equivalent to that used in treating the test portion, even if some more or less binder may be required to achieve this consistency.

Weigh, to the nearest 1 mg, between 0,1 g to 1,0 g, depending on the oil absorption value of the pigment under test.

Transfer the test portion (6.2.1) to the glass or marble plate (4.5). Run a number of drops of the binder (4.6) from the burette (4.3) on to the blade of the palette knife (4.1) and, using the blade, mix the binder and pigment. Add more drops of binder as necessary to produce a paste with a suitable consistency for milling.

When the pigment has become uniformly wetted with binder, start rubbing with the palette knife (4.1) or hand muller (4.4.2) using a backwards and forwards motion. The rubbing should spread the mixture over an area approximately 200 mm × 75 mm. After 100 rubs (one rub consisting of one forward plus one backward motion), scrape the pigment/binder mixture into a heap at the centre of the plate, making sure that any unground pigment is removed from the knife blade.

Repeat the rubbing-out operation using a further 100 rubs and then add a further few drops of the binder to obtain a suitable consistency. Mix well until the paste is homogeneous and transfer it to one corner of the plate. Clean the rest of the plate thoroughly.

Take a similar amount of the agreed sample of pigment and prepare a paste in the same way at a consistency equivalent to that used in treating the test portion, even if some more or less binder may be required to achieve this consistency.

Compare the colour of the test portion with that of the agreed sample by spreading the two prepared pastes in the same direction on the substrate (4.2) in opaque strips not less than 25 mm wide with touching edges not less than 40 mm long. Compare the colour by examining the strips in diffuse daylight on the surface or, by agreement between the interested parties, through the glass, immediately after application, using the procedure specified in ISO 3668. To achieve reproducible results, it is preferred to use artificial daylight. The visual assessment of colour differences using the components hue, chroma and lightness should preferably be performed in accordance with the rating scheme given in ISO 3668.

By agreement between the interested parties, a suitable colorimeter may also be used for making the comparison. In this case, the procedure for colour comparison shall be as specified in ISO 18314-1, where the colour differences using the aforementioned components shall be calculated as specified in ISO/CIE 11664-4. For simplified communication of results, a total colour difference shall be calculated as specified in ISO/CIE 11664-6 or ISO 18314-5.

The test report shall contain at least the following information:

a) the type and identification of the pigment tested;

b) a reference to this document, i.e. ISO 787‑1:—;

c) the binder used;

d) the procedure used (automatic muller, hand muller or palette knife);

e) the details of the procedure used when comparing the colours of the strips (see Clause 7);

f) the result of the test expressed as colour equal to, or different from, that of the agreed sample of pigment;

g) if colorimeter method is used, the colour differences in the components hue, chroma, and lightness;

h) any deviations from the procedure specified;

i) any unusual features (anomalies) observed during the test;

j) the date of the test.