A method of preparing an aluminum or aluminum alloy substrate to accept an adherent coating thereon is provided. The method includes the steps of degreasing the substrate, deoxidizing the substrate, and providing a prepaint conversion coating on the degreased and deoxidized substrate. The prepaint conversion coating composition comprises i) a source of fluoride ions; ii) a source of zirconium ions; iii) an acrylic resin; and iv) an optical brightener and forms a colorless, chromium-free conversion coating on the aluminum substrate that can be observed by exposing the treated substrate to UV light.
