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The Colour Laboratory
Introduction
Our UK based laboratory is UKAS accredited for conducting a wide range of BS, ISO, ASTM and DIN tests and this accreditation meets the requirements of EN 45001, ISO/IEC Guide 25 and BS EN ISO 9000/9002. A list of all the tests for which we are UKAS accredited is available.
We offer the following services:-
- The measurement of optical properties including colour, gloss, opacity, whiteness and yellowness.
- A consultancy service for those involved in disputes about colour matching.
Our work is not limited to paints and inks, we can also measure polymers, fabrics and cosmetics.
We hold regular training courses on Colour Measurement and Colour Control in the UK at our premises at Hampton, Greater London. These provide a firm foundation in the theory and practice of colour science. Please contact our Training Manager Elisabeth Brown for further details.
Measurement of Colour and Optical Properties
In addition to the tests listed below, we can also measure the durability and light fastness of coloured items.
Please contact Peter Collins for further details
The Colour Consultant
Over the years, we have been asked, on numerous occasions, to advise or arbitrate in disputes between customer and supplier over the acceptability of a colour match. Although each dispute is unique, they all have a common theme which can be summarised thus:-
- the customer orders painted items.
- he states that they should match a particular standard colour.
- the items are delivered to the customer. Sometimes there is more than one supplier and sometimes the same supplier delivers the items in batches over a period of time.
- on examination, it becomes apparent to the customer that the items vary perceptibly in colour.
- the customer complains to the supplier that there is a colour mismatch.
- the supplier responds stating that the colour match of the items supplied is within their manufacturing tolerances.
The reason why such disputes occur can be explained by taking the example of the Blue 109 Standard which is one of the 140 colours supplied by the British Standards Institution in the form of the BS 381 collection of standard colours. Blue 109 comes in the form of a coloured card which is intended to be used as a visual or instrumental reference for colour matching purposes. There are, however, no instructions associated with this standard or with the BS 381 collection as to how good the colour match has to be.
Now consider these two specifications:-
Specification 1: The paint finish should be BS Blue 109.
Specification 2. The paint finish should be visually indistinguishable from BS Blue 109 regardless of the method of paint application, the nature of the illumination, the angle of viewing, the degree of gloss and the colour or texture of the substrate.
Basically these dispute arise because the customer uses Specification 1 and thinks it means the same as Specification 2.
In order to avoid such disputes, the customer needs to specify not only the colour but also how close the colour match to this standard should be. The difference between two colours can be measured instrumentally (using a colorimeter) and expressed in "Delta E units" where a Delta E value of zero represents a perfect match. The greater the Delta E value, the poorer the match and as a general rule a Delta E difference of 1.0 is perceivable visually while a Delta E difference of 0.2 represents the best match obtainable for commercially produced paints. In practice there are some shades where a small change in Delta E can result in a noticeable colour change. Yellows and brown shades are particularly Delta E sensitive while reds and blues can tolerate much larger Delta E changes without perceptible colour change. Greens lie somewhere in the middle.
At first sight the simplest solution to the colour specification problem, once it has been appreciated, is to specify a match to the tightest possible specification ie a Delta E value of 0.2 or less. In practice however although top quality automotive paints tend towards this value, other types of paint may not available to such a tight tolerance. It is at this point that the situation becomes quite complex for the customer because he has to consider a number of questions without being certain of how to obtain the answers or indeed how to interpret the answers once he has them.
We assist clients with a wide range of colour specification problems and some idea of the complexity of the subject can be illustrated by considering the example of the type of questions that an architect might pose when specifying doors, windows and other building components:-
- My regular component supplier can only provide components with a Delta E match of less than 0.8. I have located an alternative source (at twice the price ) who guarantees a Delta E of less than 0.5. Do I need to spend this extra money?
- Now that I have established that a Delta E value of less than 0.8 will be acceptable for specifying this particular colour, can I assume that it is acceptable for the other colours I need?
- How will the lighting affect the colour match. Some parts of the building are flooded with daylight whilst others rely exclusively on fluorescent lights?
- In some case I need to specify the same colour in both gloss and matt finishes. Does this affect the situation in terms of perceived colour match?
- I have located the exact type of doors I need but they come from Germany and are finished in colours defined by the RAL colour standard. Is there any published information listing all the RAL colours and their British Standard equivalents?
- The factory applied powder coating finish on these windows has been damaged during installation and I need to specify a brush applied paint that I can use for remedial work on-site. What do I need to specify in order that both the colour and texture of the touch-up paint is indistinguishable from the factory finish?
It can be seen from these questions that colour specification is far from straightforward. Getting it right is not easy and getting it wrong can be very expensive.
Our consultants can act as advisors, arbitrators and expert witnesses. They can also work with you during the early stages of a project and help you to specify exactly what you need.
Please contact Peter Collins for further details