Put a drop cloth onto a table or workbench.
Empty the toolbox completely and set it on the drop cloth. Squirt degreasing dish soap into a bucket of water. Wipe the toolbox with a sponge dipped in the soapy water to get all grease and dirt off the surface area. Let air dry.
Put on rubber gloves. Dip a rag in paint thinner and wipe the toolbox down, then scrub with steel wool. This will start to remove the old finish. Scrub until the old finish substantially lightens. Wipe down with a damp rag thereafter and allow to dry.
Sand the surface with medium-grit sandpaper to get to the bare wood.
Brush on a coat of gel stain with a paintbrush. Wait about five to ten minutes, then wipe away with rags.
Brush on a coat of varnish to refinish the old carpenter's toolbox. Brush the varnish on, going with the wood grain. Let dry for at least three hours before putting tools back into the box.