To make a flat paint surface glossy, the best solution is to paint over it using a clear gloss paint. The resulting finish is glossy and shiny.
After a single coat of clear gloss, the flat finish surface looks similar to what a glossy paint's finish looks like. This is a good solution because matte or flat paint is often used to paint on walls or, in some cases, furniture. However, sometimes after the paint job is completed, the painter or homeowner might change her mind about using flat paint and prefers a glossy finish instead. In such cases, a clear gloss paint works effectively to update a room's appearance.