For my projects, I prefer a water-based finish to other solvent types because they’re better for us and the environment, they dry quickly, and they clean up with water.
Not every water-based finish is suitable to each method of application, so read the manufacturer’s advice. Brushing is the most common method, and you can use synthetic bristle brushes, brush pads, or foam brushes. You may also be able to spray the finish (the directions will tell you). Spraying is ideal for projects with small details, as it can deliver a more uniform coat.
Regardless of which technique you employ, here’s what you can do to achieve satiny smoothness. Buff your project with fine sandpaper, and wipe it with a microfibre cloth to remove any dust. The first coat of finish will raise and harden any loose fibres. Allow the finish to dry until the surface feels hard, then use 180x sandpaper and moderate pressure to remove the nibs. Again, wipe to remove dust, and recoat. Whether you apply two or five coats (depending on how protective a film you need, or your desired colour), repeat the process with 220x paper between each coat.
It’s challenging to arrive at a perfectly smooth final topcoat. The trick is to dress that surface after it’s had time to cure—at least 24 hours. Start by lightly sanding with 320x to 400x paper. Remove the dust, and lightly rub with #0000 steel wool until your project has an even sheen. Wipe off the dust for the last time, followed by a brisk rub with a wadded piece of old denim for a satiny gloss, and voila!