Most gilders agree that for most sign applications, you should not clear coat 23-karat gold leaf. What differentiates gold from other metals is its brilliance. Clear coating diminishes its shiny surface.
But as with all rules, there are exceptions. If it is likely that the general public will put their grubby mitts on the gilded surface, by all means clear coat it. Remember body oils and perspirations will tarnish the gold.
If you decide to clear coat your work, you have a few options. For gold leaf projects, Butch Anton’s Frog Juice is always a popular choice, as is Rolco’s solvent-based acrylic topcoat. These coatings provide good protection from abrasion, chemical spillage, and the degrading effects of UV light. Before using any clear coat in production, my advice is: “Test. Don’t guess.”
Before using any clear coat, stir the can slowly. Slowly is the operative word; you don’t want to create bubbles in the clear coat. Usually you can use clear coat straight out of the can. However over time, these coatings can thicken and will require thinning with either mineral spirits or turpentine.
Be sure to follow the manufacturer’s application instructions. After one to three hours, the clear coat should be dry to the touch. After twelve hours, it should be fully cured.