Visual Colour Comparison


BS EN ISO 3668: BS 3900-D1

 Visual Colour Matching

Scope and Field of Application

BS EN ISO 3668 and BS 3900-D1 are alternative names for the same method of carrying out a visual comparison of the colour of paint films or related products with a standard colour under natural or artificial lighting conditions.

Visual colour matching 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 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.

Colour matching is a complex subject and one that is liable to give rise to disputes. This aspect is dealt with in greater detail on our colour laboratory page.

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

The actual standard is a copyright-protected document and we are not able to provide you with copies. If required however, you can easily obtain copies from the British Standards Institution.

 

Summary of Method

The standard describes how the colour vision of observers should be checked and how eye fatigue should be avoided. The point is made that observers need not only normal colour vision but also the ability to discriminate between colours. The latter is developed by both training and experience.

Colour matching in daylight is carried out with the observer facing away from the equator with the samples illuminated by diffuse daylight from a partially cloudy sky.

When colour matching under artificial illumination is required, this is carried out using a colour-matching booth fitted with the following lamps:-

In addition we use:-

The standard gives details of the construction and illumination of the booth and the way that it should be used to view the samples. It also describes how metamerism is assessed. Metamerism defines the situation where the colour of the sample and the standard match under one illuminant but not under another.

The observer reports the results of the visual colour comparison using a six-point rating scheme given in the standard. This ranges from imperceptible to major colour differences.

 

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.

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

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

 

Accreditation

PRA is accredited to ISO 17025 by the United Kingdom Accreditation Service (UKAS) to carry out this test.

 

 

Please contact Peter Collins for further details.

Back to top of page

 

Back to Paint Testing Laboratory Page

Back to Testing Applied Paint Films Page

Back to Colour Laboratory Page