While in many circumstances strength and ease of application is the bottom line for adhesive manufacturers, in others it is more important that the appearance is right. In fact, fastening materials together in an attractive manner often drives manufacturers to adhesives, away from rivets, screws and bolts. By contrast, visual appearance is often an afterthought when formulating an adhesive, but in fact there are crucial scientific principles that can be exploited in delivering the best looking adhesives.
For the most basic formulations, the colour of the final adhesive is simply determined the colours of the components combined in the final product. This approach may seem appropriate for only low-specification applications, but actually it can lead to some useful visual indicators of an adhesive's functionality. For example, an adhesive that is heavily loaded with iron oxide to provide thermal conductivity will be easily distinguished by its red colour. Similarly, carbon black pigments will impart limited electrical conductivity.