Many industries employ colouring processes designed to enhance colour uniformity, recognition or aesthetic appeal. The producer must deliver a product of the desired colour with its variation controlled to an extent appropriate for the application and the customer’s expectation. The manufacture of pigment pastes is a blend of art and science.

Before making a pigment paste, the manufacturer is confronted with several questions. What is the end application? Where is the FRP component being used? Is it outdoors? Is it under water? Is the water saline? What is its temperature? Does the application call for translucency in the FRP component? Or should the FRP component be opaque? Will the FRP component be moulded at room temperature and low pressure? Or will it be moulded at elevated temperatures and high pressure? Only after the manufacturer has answered all these questions, does he talk of colour matching and shades. Here too, he has to think of loading of the pigment into Resin or Gelcoat. Pastel shades need more loading whereas darker colours require very little.

In terms of the basic pigments, there are several options from which to choose. There are Organic pigments and Inorganic pigments. Each group has its own set of properties, which influence how the final FRP product is going to look. Then there is the resin medium. It is a specially designed polyester resin that has to work synergistically with the pigment powder and yet be compatible with the plethora of resins and gelcoats available in the market place.

Contrary to popular belief, colour matching is not purely an art. It is a mathematical science governed by three of Grassmann’s Laws:

• aQ1 + bQ2 = cQ3 + dQ4 i.e. 4 colours Q (1 – 4) are always related so that a match can be expressed by this equation, where a, b, c and d are not all zero and one or more can be negative multipliers.
• If the multipliers are further multiplied by a constant, the match will still be maintained i.e. CKaQ1 + CbQ2 = CcQ3 + CdQ4
• Many colours can be matched by additive mixtures of appropriate amounts of the 3 primary colours: Q(Q) = R(R) + G(G) +B(B) Any of the two primaries cannot be matched by additive mixtures of appropriate amounts of the 3 primary colours: Q(Q) = R(R) + G(G) +B(B) Any of the two primaries cannot be matched by a mixture of the other two.

By the same token, Colour Strength Absorption (K) determined by the colorant and Scattering Constants (S) determined by the substrate influence the Chromatic Strength which is the measure of the tinting strength of the colorant.
% Strength = (K/S) of the batch x 100
(K/S) of the Standard

When we talk of ‘tailor-made’ products, we mean not only from the point of view of colour and shade. The extent and chemical nature of the Toners, Extenders also influence not only how the colour will look but also how it will behave with extended weathering. Needless to add, that there are an equal variables at moulding stage: the gelcoat and its activity, the fillers used in making it, the activity and percentage of the catalyst and accelerator, and finally the substrate itself.