Clean the chipped tile with a soapy sponge and rinse well. Dry the chip for at least 15 minutes with a hair dryer---ceramic tile can retain moisture long after it appears dry to the naked eye.
Paint a thin coat of oil-based primer/sealer into the chip. Take care to not get any primer on the unchipped part of the tile. Allow the primer to dry for two hours.
Paint a thin coat of high-gloss oil paint over the primed chip. The color of the oil paint should match the surrounding tile as closely as possible. Visit a specialty hobby or paint shop to check small containers of high-gloss oil paint for a close match. Allow the paint to dry for 24 hours.
Adjust the color of the painted chipped area, if necessary, with a second coat of high-gloss oil paint. Allow the final coat to dry for 24 hours before continuing.
Mix the two-part marine epoxy on a piece of scrap cardboard with a toothpick. Mix equal amounts of each part of the epoxy mixture.
Dab the marine epoxy into the painted chip with the end of the toothpick. Continue adding epoxy until the level of the epoxy over the chip matches the level of the rest of the tile. Allow the epoxy to cure for 24 hours undisturbed.