Coated articles demonstrating anti-fouling properties are provided, comprising: (a) a substrate comprising sapphire; (b) an adhesion promoting layer applied to the substrate; and (c) a top layer comprising at least an anti-fouling coating applied to the adhesion promoting layer. The adhesion promoting layer is formed from a curable sol-gel composition and has a dry film thickness less than 1000 nm after curing. The present invention also provides a method of forming a coated article comprising: (a) applying a curable film-forming sol-gel composition on a sapphire substrate, to form a coated substrate with a sol-gel adhesion promoting layer having a dry film thickness less than 1000 nm after curing; (b) subjecting the coated substrate to a temperature of at least 500° C. to effect cure of the sol-gel composition; and (c) applying at least an anti-fouling coating on the adhesion promoting layer to form a multi-layer, coated article.