Before the use of latex paint became widespread, people counted on enamel paint as an oil-based product that produced a glossy finish. Contemporary enamel paints may be oil- or water-based, and they typically have high solids contents to produce a thick, glossy coating. Because the percentage of pigment and solids is high in relation to the solvent and binders, enamels can take longer to dry and cure than ordinary paints -- but you can shorten these drying times.
Drying Time and Curing Time
All paints, including enamels, dry when the solvents carrying the solids that remain on the painted surface evaporate. This is a two-step process for some water-based paints, because the emulsions carrying acrylic latex resins don't evaporate until the bulk of the water does. After the paint is dry to the touch, the curing process begins, and this takes much longer than solvent evaporation -- from two weeks to a month. During this time, the paint becomes increasingly less vulnerable to scratching and other damage as it approaches its maximum hardness.
Speeding Up Solvent Evaporation
It takes longer for water, mineral spirits and other solvents to dry if the air is cool and moist, so you can speed up drying time by decreasing humidity and raising temperature. If you're painting indoors, run a heater and dehumidifier or turn up the central heating system, and if you're painting outdoors, start the job at the beginning of a warm, dry day. Circulating air also increases the rate of evaporation, but do this with care. If you use a fan to increase airflow around an interior paint job, make sure the air is free of dust and other particles that can land on the paint and get stuck.
Add Japan Drier
If you're painting with oil-based enamel, you can speed up the drying time by adding Japan Drier. This naphtha-based additive doesn't come from Japan -- it gets its name from its ability to make an oil-based surface resemble Japanese lacquer. It contains a metallic salt -- usually cobalt -- that increases the rate of oxidation of the oils in the paint. Use it in small quantities -- typically an ounce or two per gallon of paint -- because it can darken the final color and cause cracking and other defects by making the paint dry too quickly.
Speeding Up Curing Time
During the paint curing process, the molecules interlink to form a solid membrane, and they need oxygen for this. This means you can speed up curing time by increasing the amount of available oxygen. It's safer to use fans during the curing process than it is to speed up drying, because the painted surface is hard and won't collect dust. Increasing the heat in the immediate environment of the painted surface also helps increase the rate of oxidation and lower the curing time. Check the new paint by making an indent with your fingernail before putting weight on it; if your fingernail leaves a dent, the paint needs more curing time.