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Colour and optical properties

The BS and ASTM standards mentioned here are copyright-protected documents and we are not able to provide you with copies. If required however, you can easily obtain copies from the British Standards Institution or the American Society for Testing and Materials.

Test Standard
Colour Comparison (Instrumental)BS 3900-D8: ISO 7724/1
Colour Comparison (Visual)BS EN ISO 3668, BS 3900-D1
Determination of OpacityBS 3900-D11, ISO 6504/3
Determination of OpacityBS 3900-D4, ISO 2814
Determination of OpacityBS 3900-D7, ISO 6504/1
Determination of Opacity: in-house method
Determination of Whiteness and YellownessASTM E313
Gloss MeasurementBS EN ISO 2813, BS 3900-D5

Colour Comparison (Instrumental): BS 3900-D8: ISO 7724/1

Scope and Field Application

These three British Standards (BS 3900-D8, BS 3900-D9 and BS 3900-D10) and their ISO equivalents (ISO 7724/1, ISO 7724/2 and ISO 7724/3) are intended to be used together by those wishing to carry out an instrumental comparison of the colour of paint films or related products with a standard colour.

Instrumental colour matching has the advantage that it can provide reproducible data regarding the closeness of a colour match. The disadvantage is that the data generated may not always correlate with the way that the human eye perceives colour.

In such cases you should consider visual colour matching. This has the advantage that it provides information on how the colour is perceived which, arguably, is the only thing that really matters. The disadvantage of visual colour matching however is that it relies on the opinion of an observer and may well result in disagreement between observers.

In our opinion there is no need to choose between instrumental and visual colour matching. The most satisfactory way to compare colours is to use both methods.

There are no pass/fail criteria defined in the standards. This is a matter of agreement between the parties concerned.

Sample Requirements

We need to be able to press the sample against the port of the spectrophotometer in such a way that no light can leak past the sample and interfere with the measurement. Ideally the test sample and the reference colour standard should be flat panels about 150 x 100 mm. The paint surfaces should be smooth or lightly textured and the substrates should not be perforated. Provided the other requirements apply we can work with samples as small as 10 x 10 mm and as large as 300 x 300 mm

If you wish, we can prepare the test panels. The quantity of liquid paint we need depends on the method of application. We will be pleased to advise you regarding our requirements.

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Colour Comparison (Visual): BS EN ISO 3668, BS 3900-D1

Scope and Field Application

Visual colour matching has the advantage that it provides information on how the colour is perceived. The disadvantage of visual colour matching however is it relies on the opinion of an observer and may well result in disagreement between observers.

In such cases you should consider instrumental colour matching. This has the advantage that it can provide reproducible data regarding the closeness of a colour match. The disadvantage is that the data generated may not always correlate with the way that the human eye perceives colour.

In our opinion there is no need to choose between visual and instrumental colour matching. The most satisfactory way to compare colours is to use both methods.

There are no pass/fail criteria defined in the standard. This is a matter of agreement between the parties concerned.

Sample Requirements

Ideally the test sample and the reference colour standard should be flat panels about 150 x 100 mm wherever possible the sample and reference panels should be similar in size, gloss and surface texture.

Only one sample panel and one reference panel is required for each determination. We have collections of BS and RAL colour standards which we can use should you require your sample to be compared with one of these references.

In many cases it is possible to adapt the method to compare the colour of samples other than test panels. Examples include building components, automotive parts, electrical components and display/packaging material.

If you wish, we can prepare the test panels. The quantity of liquid paint we need depends on the method of application. We will be pleased to advise you regarding our requirements.


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Determination of Opacity: BS 3900-D11, ISO 6504/3

Scope and Field Application

BS 3900-D11 and ISO 6504/3 are alternative names of a method for determining the opacity of paints. In our experience it is most widely used method.

There are no pass/fail criteria associated with this standard. This is a matter of agreement between the parties concerned.

Sample Requirements

This method is only applicable to white or light coloured paints and not applicable to paints which are textured or those which fluoresce or have a metallic finish.

We require 250ml of paint

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Determination of Opacity: BS 3900-D4, ISO 2814

Scope and Field Application

BS 3900-D4 and ISO 2814 are alternative names of a method for comparing the opacities of paints. It is relatively simple in operation.

There are no pass/fail criteria associated with this standard. This is a matter of agreement between the parties concerned.

Sample Requirements

This method is only applicable to white or light coloured paints and not applicable to paints which are textured or those which fluoresce or have a metallic finish.

We require 250ml of paint.

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Determination of Opacity: BS 3900-D7, ISO 6504/1

Scope and Field Application

BS 3900-D7 and ISO 6504/1 are alternative names of a method for determining the opacity of paints. It is mainly used for checking that coatings meet the requirements of the Ecolabel scheme.

 

Sample Requirements

This method is only applicable to white or light coloured paints and not applicable to paints which are textured or those which fluoresce or have a metallic finish.
 
 
We require 250ml of paint.

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Determination of Opacity: in-house method:

Scope and Field Application

In addition to these standard methods, we also carry out an in-house method whereby paint is applied to a surface which includes a contrasting background. This gives a measure of both the opacity of the coating and its application properties.

There are no pass/fail criteria associated with this method. This is a matter of agreement between the parties concerned.

Sample Requirements

Provided the paint can be applied by brush or roller to yield an air-drying film, then we can test it.
    
We require 2.5 litres of paint

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Determination of Whiteness and Yellowness: ASTM E313

Scope and Field Application

In many cases the ageing of white paints in service is accompanied by yellowing.

The standard details the theory and practice associated with the use of a spectrophotometer to determine whiteness and yellowness. It is appropriate to use the same standard method for determining both values as the same equipment and experimental techniques are used and only the methods of calculation differ.

Whiteness is defined as a measure of how closely a surface matches the properties of a perfect white diffuser i.e. an ideal reflecting surface which neither absorbs nor transmits light but reflects it at equal intensities in all directions.

Yellowness is defined as a measure of the degree to which the colour of a surface is shifted from preferred white (or colourless) towards yellow.

There are no pass/fail criteria defined in the standard. This is a matter of agreement between the parties concerned.


Sample Requirements

We need to be able to press the sample against the port of the spectrophotometer in such a way that no light can leak past the sample and interfere with the measurement. Ideally the test sample should be a flat panel about 150 x 100 mm. The paint surfaces should be smooth or lightly textured and the substrates should not be perforated. Provided the other requirements apply, we can work with samples as small as 10 x 10 mm and as large as 300 x 300 mm.

If you wish, we can prepare the test panels. The quantity of liquid paint we need depends on the method of application. We will be pleased to advise you regarding our requirements.

We have also used this method to measure the whiteness of pigments and extenders. About 100 grams of sample will suffice for this purpose.

It is also possible to use the spectrophotometer in the transmission mode to measure the yellowness of transparent solids or liquids. In the case of solids the sample size required is 50 x 50 x not more than 25 mm. In the case of liquids, 50 ml will suffice.

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Gloss Measurement: BS EN ISO 2813, BS 3900-D5

Scope and Field Application

BS EN ISO 2813 and BS 3900-D5 are alternative names for the same method for measuring specular gloss of non-metallic paint films. Specular gloss is defined as the perception by an observer of the mirror-like appearance of a surface. In truth this appearance cannot be quantified all that can be done instrumentally is to measure the amount of incident light that is reflected at a defined angle or range of angles.

Glossmeters are simply devices that illuminate a test surface at a defined angle of incidence and measure the amount of light at a defined angle of reflection.

Specular gloss is quantified by measuring the amount of light reflected from the sample and comparing it with the amount of light reflected when a polished black glass calibration standard is measured under the same conditions. The glass standard is assigned a value of 100 gloss units and in practice the highest attainable gloss values for non-metallic paints tend towards 95 gloss units. It follows from this definition that any surface that reflects more light than the black glass standard will produce a glossmeter reading of greater than 100 gloss units. Metallic finishes (of the type used as automotive paints) will generally produce glossmeter readings well in excess of 100 gloss units and this standard does not cover the measurement of gloss on this type of coating.

There are no pass/fail criteria defined in the standard. This is a matter of agreement between the parties concerned.

Sample Requirements

We require one coated panel about 150 x 100 mm. The paint surface should be smooth or lightly textured and the substrate should not be perforated. We can work with samples other than test panels provided these restrictions apply and provided we have about 150 x 100 mm of flat surface available.

If you wish, we can prepare the test panels. The quantity of liquid paint we need depends on the method of application. We will be pleased to advise you regarding our requirements.

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