Hardware stores sell little jars of touch-up enamel that look just like nail polish jars, with a built-in brush. They come in various colors. They use a volatile solvent which is toxic for a few minutes, but after an hour or a day they should have no odor at all. Also there are mobile enamel repair services that use an epoxy for the same purpose, I do not know if they have a residual odor or not. Test everything first on a piece of scrap metal or glass or tile, but to be safe, wait a few days before sniffing.