A shellac finish has been used by woodworkers since the early 1800's. It has many advantages: shellac is non-toxic, can be used as a sealer before applying a stain (to even out the stain's application), can be mixed with nearly any color, and is very easy to repair in the event of damage from use.
That being said, there are some drawbacks to using shellac as a final wood finish. Shellac does not hold up well to heat or water, and it dries very quickly when being applied, which leads many woodworkers to believe that applying a proper shellac finish can be difficult.
What is Shellac?:
Shellac is derived from a resin that is secreted from an insect native to certain forests in southeast Asia. This insect secretion is scraped from the bark of trees and, when processed, takes the form of small, light-brown or orange flakes.
To make an applicable woodworking finish, these flakes are mixed with alcohol. Woodworkers commonly use a two-pound-cut finish, which is to say a ratio of two pounds of shellac flakes per gallon of alcohol. Pre-mixed shellac found in home centers may be three-pound, but this can be cut if desired (typically, the measurements for cutting are listed on the can).
There are two commonly accepted methods for applying shellac: brushing and padding. To brush on shellac, use a fine, natural or china-bristle brush. Use a two or three-pound cut of shellac and apply generously with long, smooth strokes. Because shellac dries quickly, be careful to avoid drips or blotchy areas when applying, because unlike other finishes, you will likely not have time to over-brush to eliminate the blemish.
To apply shellac with a pad, use a clean piece of medium-weight cotton muslin. The idea is to lay down a smooth, even application of shellac in a single long, even stroke.
While many techniques for padding are used, a favorite that I recently learned is to wrap a ten-inch square piece of muslin around an old (clean) athletic sock.
Before beginning to apply the shellac, place your cut of shellac into a squeeze bottle. Squeeze a liberal amount of shellac into the sock to act as a reservoir. Then wrap the muslin around the sock and hold the edges of the muslin behind the sock.
Squeezing the pad lightly should allow a small amount of shellac to seep through the muslin. The exposed shellac on the muslin surface of the pad should be even with no dripping.
When applying the pad to your woodworking project, you may need a bit of a lubricant. Mineral oil works great, as it will not affect the final color or finish. If your padding movement seems a bit "sticky", keep a small bowl with a little bit of mineral oil handy for light dipping.
With a very small amount of mineral oil on the loaded pad, you're ready to begin applying the shellac to the wood. To start, do not place the pad directly onto the wood and begin rubbing; instead, ease the pad on and off the stock to avoid any blotchy spots. The best way to describe the motion is to work much like an airplane taking off and landing.
Once the pad is on the wood, work in somewhat irregular patterns rather than just with the grain. This will ensure a thorough coverage. As you need more shellac, simply squeeze the pad a bit.
A more traditional method of padding is to fold a piece of muslin a few times so you have a flat pad with a few layers of thickness. Then apply light coats of shellac with a moist, but not dripping wet pad.
No matter which method of padding you choose, you'll find padding works best on flat surfaces. Irregular areas, corners, and trim will likely be easier to apply with a brush.
Many woodworkers like to use a combination of brushing and padding. They will apply the shellac with a brush, then immediately smooth it out with a piece of muslin. Use long strokes moving with the grain of the stock.
Completing the Shellac Finish
After the first coat of shellac dries, lightly sand with 400-grit sandpaper. Wipe off the white residue and apply a second coat. Repeat until the desired number of coats have been applied.
This direct application will result in a high-gloss finish. If a less glossy, satin finish is preferred, try buffing out the final coat with some 0000 steel wool and (non-silicon based) paste wax. Lightly work the wax over the finish until it is thoroughly covered. Allow the wax to dry, then wipe off and buff to a lustrous finish.
Brushes can be easily cleaned after applying shellac with alcohol, as this will effectively cut the shellac until the brush is clean. However, I find a simpler method is to clean the brush with ammonia. The alkaline ammonia dissolves the shellac quickly and easily. After the shellac is completely gone, wash the brush in soap and warm water to keep the bristles soft. Dry the bristles and store the brush in the container in which it came (to keep the bristles in proper shape).
Repairing Shellac Finishes
Shellac finishes should be kept away from water, as they will become dull or even have a white residue appear when exposed to moisture. Should your shellac finish develop water spots, repair is relatively simple. Use straight alcohol on a pad and remove the shellac from the offending area. Then pad or brush on a series of coats of shellac and rub it out until the finish is even.
Should a surface scratch appear through the finish, use a fine artist's brush to fill the scratch with shellac. Rub out the finish to even out the color between the repaired scratch and the surrounding finish.