There is a similarity between the two phenomena in as much as both effects are due to the reflection of light by the pigment particles. From the application point of view however, there is a major difference. Bronzing is regarded as a drawback and is found mainly in organic coloured pigments such as the phtalocyanins if their particles are more strongly oriented in the paint film and if their refractive index is very different from that of the resin matrix.
An unwelcome metallic Iustre will then be superimposed on the actual colour. "Flop“, on the other hand, is a desirable effect in metallic finishes. Here, the pigments are aluminium powders and these, too, exhibit a metallic Iustre as a result of particle orientation. This means that there are marked changes in intensity of light reflection as the angle of observation changes.