*3.4.1. Surface gloss of sol-enhanced coatings*

Surface gloss and color is important properties for gold and many other coatings as it dictates the quality and value of many products. Delta E (ΔE) is widely used to present the colour difference between samples being compared. It is generally accepted that if the difference of ΔE value between two samples is less than 1.0, they can be considered as the same colour, while 3.0 is the smallest colour difference that can be recognized by human naked eyes.

Fig. 10 presents the ΔE-values of Au-Ni coatings with different dopants. It can be seen that the sol addition impose a weak influence on the surface gloss and colors of coatings, which even cannot be detected by human naked eyes. The sol-enhanced coatings present almost identical surface gloss with the traditional coating due to the highly dispersed nano-structure [25].
