Paint is a basic finish that covers and protects the material that it's applied to. Paint isn't usually used over natural wood, but it can be. If the paint coverage is thin, or semi-transparent, then the wood grain can show through, with dramatic effect.
Paint is commonly used on woodworking projects made of MDF or plywood, as well as woodworking projects that require color.
Stain is usually used over natural woods, or plywood, so that the grain is visible and accentuated. It can really make wood pop and add warmth to not so fancy woods.
The purpose of clear coats is to seal and protect the wood, while allowing the grain to be seen. No need to hide beautiful wood, right?
There's quite a few options to choose from, so let's take a look.
Wax is a simple finish to apply, as it's simply rubbed on a buffed to a sheen. It works best on fine-grained woods that have been sanded to a smooth surface. It's not best on rough-grained woods, such as Oak or Ash.
Wax is not only applied to bare woods, but also on top of over finishes, such as Shellac, to protect them from moisture.
Oils are an easy way to finish woodworking projects as they are simply applied heavily then wiped down to a dull sheen. They are quick to apply and can be re-coated over the years. Oils do not provide a shiny surface, though and may feel sticky for some time.
Here's a few options if you want to wood finish your projects in oil.
Linseed oil is made from flax seeds. It's applied by brushing or wiping it on in coats and wiping it down with dry rags until the desired protection/finish is achieved.
Tung oil is similar to Linseed oil. It's made from the kernels of Tung tree seeds. Like Linseed oil, you you brush or wipe it on, then wipe off the excess. It protects the wood without providing much shine.
Mineral oil is applied like Linseed Oil and Tung Oil. So, why is it mentioned? Well, when purchased in food safe grades it can be used on childrens' toys and cutting boards.
Shellac is an age old finish that's not used much these days. Shellac is a resin that is dissolved in alcohol and then brushed on to projects. It's not known for it's moisture protection, so it's fallen out of favor over the years. Warm coffee cups, or plates, will leave a ring in a shellac finish, as will sweaty cups. It's not the best choice for table tops.
Varnish is also a resin and solvent based finish, similar to shellac and lacquer. Varnish is usually wiped or sprayed on. More durable than shellac, varnish will stand up to moister. Spar varnish is used in wooden boat applications.
Unlike oils, lacquer dries by solvent evaporation to a hard and durable finish that does not need re-coating. Lacquer can also be polished, but is available in matt and satin finishes. Lacquer can be applied by brush or by spraying. A solvent is necessary to clean the brush or spray gun.
Lacquers dry much quicker than oils, so finishing can be done more rapidly. Since lacquers dry hard, they are prone to cracking and chipping with age.
Polyurethane is basically a liquid plastic that provides a durable finish when it cures. It's available in gloss to matt finishes and is applied by wiping, brushing, or spraying. A solvent is necessary to clean the brush or spray gun. Polyurethane does not dry quickly, so it will take a bit of time to finish your project.
Due to it's slow drying time, polyurethane is prone to collecting dust as it sets up. Keep this in mind when you choose where to finish your projects.
Polyacrylic is a water based polyurethane which dries quickly to a tough durable finish. It cleans up with soap and water and is usually applied by brushing or spraying. Polyacrylic is a very easy to use and clean up, so it's gaining great favor with woodworkers.