New wood is usually milled to perfection, with straight lines, smooth surfaces and clear, bright grain. It has no scratches, stains, holes, cracks or dents and is a clear light colour. But if you want to use new wood to repair something old and rough (like bare floorboards) or you are aiming for an old, rustic look on a piece of furniture, then bright, shiny new wood must be aged. This means creating those imperfections that come with age--including dents, marks and scratches plus making the wood darker and lifting the grain so it is not so smooth.
Create irregular dents on the wood by beating it with a chain or by putting a handful of irregularly sized nuts and bolts into a pillowcase and bashing it against the wood. Make sure you create irregular dents, as regular damage looks unnatural. Start with only a few dents and see how it looks. If it needs more dents, then beat it again, but don't overdo it as too many dents will look fake.
Create a few scratches (only a few) with a sharp knife or a pair of scissors. If you want to create woodworm holes, hammer a thin nail or panel pin into the wood to punch a few very small holes. Cluster the holes in one small area--do not place them uniformly or in a regular pattern.
Sand off any sharp edges or corners. Use coarse sandpaper (40 to 80 grit) wrapped around a small block of wood. Old wood usually has rounded edges and corners. Do not make the rounding-off regular and smooth. Vary the depth and angle of the sander slightly, and add a dent or two by hitting the edge with a hammer.
Raise the wood's grain by wetting it with water. To create a rough surface, sand with coarse sandpaper or scrub with a scrubbing brush or wire brush.
Darken the damaged areas of the wood by wiping a dark brown stain over the dents and scratches and wiping off the excess with a cloth wrapped around a small block of wood. The cloth must be kept flat so it wipes the stain off the surface and leaves the stain in the dents and scratches. The aim is to make the damaged parts look darker.
Change the colour of the wood to a darker, greyer tone by applying a grey-brown stain (or mix grey stain with brown stain). Apply thinly and wipe off any excess quickly. The longer the stain is left on the wood, the darker the wood will become.
Other ways to make the wood an old grey-brown colour include wiping with strong tea or coffee, or with grey and brown shoe polish. You can also use caustic soda (lye), but be very careful as this is highly corrosive and may burn your skin or damage your eyes. Always wear protective clothing, including rubber gloves and safety glasses. Caustic soda damages the wood, so if you want a really rough look, then this could be the solution. Neutralise the caustic soda by wiping it with a solution of vinegar and water.
Have a close look at some actual old wood to see how the marks, dents and flaws appear. Notice how many there are and how far apart. Damage such as marks and scratches will be irregular. Start slowly and see how the wood looks with only a few flaws. It is tempting to overdo the beating and scratching, but this ends up looking artificial. It may only take a few dents and nicks, plus a change of colour and surface texture, to create an effective old, rough look.
Wear protective clothing, a respirator and safety goggles when handling caustic soda as it is dangerous. Caustic soda can create a fine mist, which can damage the eyes and lungs, and it burns the skin very easily. The methods described here are designed to make the wood look old and rough. If you are after a smooth or antique look these methods will not create the right effect. Antiquing wood and achieving a smooth finish involves layers of colour, texture and polish and does not damage the wood as much.