Ref: G024 v1.1 Dec 2016

Introduction

Coatings are used for the protection and decoration of buildings, structures, vehicles and articles. Coatings are applied to various substrates including wood, plastic, metal, and building materials. Colour accuracy, consistency, and ensuring the correct specification and colour shade is selected, are of prime importance to coatings manufacturers, coatings applicators and end customers.

It is possible for colour differences to be perceived on the final coated substrate for a number of reasons, some of which may be unavoidable due to the coating and application technology. Colour variations can be caused by a number of factors including different substrate, film thickness, gloss level, angle of viewing, smoothness of film, application and drying method, application and paint conditions, and lighting type.

Applied coatings may differ in colour from an agreed standard; in addition, there may be batch to batch variations. The magnitude of any perceptible difference between two colour tones may or may not be acceptable to the customer. A colour tolerance value nominally acceptable on paper can give rise to a distinctly appreciable colour deviation due to how humans visually perceive colour.

It should be noted that coatings are industrially-manufactured products and, as such, are subject to inherent deviations owing to their industrially-manufactured raw materials and their preparation processes.

Metallic and effect shades (e.g. aluminised or pearlescent finishes) are very complex with regard to colour and so are not included in this guidance document.

Colour Appearance

Colour appearance can be influenced by a number of variables. One of the most important of these is the light source. Apparently similar colours formulated using different colourants can appear very different when viewed under different lighting conditions. This is known as metamerism . Certain colours can be more prone to metamerism than others. To minimise the potential for metamerism, the aim should be to use, where possible, the same choice and combination of colourants to those used in the original colour, and no more than four colorants. Coating manufacturers rely on light boxes with specified lighting sources included, to standardise the colour comparison procedure e.g. D65 (artificial daylight), CIE Illuminant A (tungsten filament light), TL84 (fluorescent light). It is vital to ensure these are well maintained.

Colour Matching

Due to the variations for finished coated objects and building components, it is important for any two coatings to be compared under the same circumstances, i.e. samples must be applied on test panels under stated standardised laboratory conditions.

Continue reading.