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Colour Tolerances
 

Among the most frequently asked questions to the RAL Colour Chart Service are questions about the allowable deviation of colour deliveries or coloured objects from RAL charts forming the basis of the respective order. These questions always have the character of complaints and the less experienced the questioner is the more indignant he/she becomes when learning that RAL does not set any limits beyond which a RAL Colour is no longer a RAL Colour.

Big colour users have specialized staff and facilities to sufficiently check the colours and make sure that their perception of colour is met. Apart from that, they can set binding limits right from start because they are familiar with the subject and normally use colour exclusively or primarily for one certain field of use. Here, fixed agreements are possible and verifiable and that is why RAL does not receive any questions concerning colour tolerances from these circles of colour users.

Disadvantaged are small and medium-sized customers who do not only lack colour measurement instruments but also colour-theoretical experiences. As long as single objects are painted or coated the problem may be minor. But especially firms of this size often act as sub-suppliers which means that their products are combined with third-party products.

Here, it may be a prerequisite or even a condition of delivery contracts that the surfaces are identical with others as far as colour is concerned. As practice shows, this often leads to disputes which for the lack of standards result not only in modifications but also in price reductions, subsequent improvements or the like.

Those who seem to be particularly concerned in this respect are the manufacturers of metal construction elements irrespective of whether they do the coating themselves on a small scale or buy undercoated flat products. Because of their surface design such elements very distinctly reflect their colour impression and are particularly often combined with built-in parts made by other manufacturers, whether these are doors, luminous strips or coverings.

When starting to think about how - even after coating with the same lacquer charge - different surface structures take additional influence on the colour impression and about the problems arising from the frequent co-existence of different coating processes, such as spray painting, powder coating etc. the term "non-calculable risk" readily comes to one's mind.

Such consequences are, however, not necessary. On the other hand, the situation of being dependent in many cases on the emotional assessment of the magnitude of colour deviations is by no means satisfactory.

There should at least be the possibility to follow established guidelines in cases of dispute. For this purpose, smaller companies too should get access to colour measurement by placing a corresponding order. What is needed are guidelines similar to the one established by DIN 6175 for car refinishing.

Here, a restriction of the scope of applicability of one RAL Colour number to a certain central colour location won't be of any help. The main reason for this pointlessness is the simple fact that depending on the field of production limited or "very wide" deviations are tolerated and that a general determination of colour limits would, in any case, be detrimental to one of these fields.

Since the colour of a product as one of the product's quality criteria assumes similar or sometimes even greater importance than other product elements the elaboration of tolerance guidelines, at least as a recommendation, would be a challenging task for those concerned.

For the time being, the agreement on pre-samples of suppliers which upon approval are signed and made an integral part of the contract continues to be the most reliable procedure to avoid complaints for customers without colour measurement instruments.

RAL Colour or Not?

When ordering on the basis of RAL numbers there should not be any problem as a certain colour shade is assigned to each number. It is RAL's task to provide the corresponding colour samples. Colour manufacturers use the binding colour charts of the Registers 840-HR and 841-GL as a model as well as for quality control during production.

Colour deviations often lead to problems in cases where parts of different suppliers need to be combined. Here, even the slightest deviations can be noticeable. Then RAL regularly gets asked the following questions:

  • Which is the "right" RAL Colour?
  • When is a colour still a RAL Colour and when not?
  • Who is going to help in cases of dispute?

In reply to these questions it may be stated:

The original register cards issued by RAL show the colour assigned to a certain number. They should be the basis for comparison.

As RAL Colours can not only be used by everyone but also for every purpose RAL considers itself unable to control the products manufactured on the basis of RAL Cards. That is why RAL does not prescribe any colour tolerances as they are subject to different trade-specific requirements.

In the case of apparently unsatisfactory deliveries only a sworn expert will be in the position to provide help. The address of a competent expert can be obtained in Germany from the Chambers of Industry and Commerce, Chambers of Crafts and from the local courts.

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