The first step in reactivating the old finish on your wood furniture is to identify what type of finishing product was used in the first place. The simplest method of determining what finish was used is to perform a test, in a spot that is not very noticeable, using solvents. The solvent will tell you exactly what type of finish you are dealing with. For example if the finish softens using turpentine, varnish is the finish. Likewise, shellac will soften when you rub it with denatured alcohol. Lacquer will only be affected by lacquer thinner. Before you do the test, remove any wax that is on the table — the wax will have to be removed from the entire surface in any case.
A number of different mixtures and concoctions are available to remove marks on varnished furniture, marks like those made by plates, glasses, water, perfume, alcohol and so forth. There are many effective methods. Most of the mixtures you can make yourself.
The first method requires a paste. The paste is made with finely powdered pumice and linseed oil. Add just enough linseed oil to the pumice to make a paste that is slightly thick (tacky enough that it sticks to your fingers, but not as thick as peanut butter). Remember to remove any wax that may be on the surface before you begin.
Use the paste with a clean soft lint-free cloth and lightly rub the surface in a circular fashion. Continue rubbing for a minute or so and then wipe the surface clean to see if the spot is gone. Re-wax the whole surface when you are done.
Another method of spot removal is using cigar ash or table salt and mineral oil. After you’ve removed any wax on the surface, dip the tip of your finger into the oil and then into the cigar ash or salt. Rub the spot lightly. Check your progress often to see if the spot has disappeared. When finished wax the surface.
The best method for surfaces that have turned white from water is French polishing; it is also a good procedure for removing light surface cracks and scratches.
This is very similar to the finish used in decoupage where numerous coats of shellac are applied and painstakingly rubbed to a deep high quality sheen. Thin the white shellac with alcohol to a one-pound cut (this refers to the pounds of shellac resin dissolved in a gallon of solvent.) This mixture is then applied with a soft, lint-free cloth that is gathered into a ball.
Dip the ball into the shellac and rub it onto the surface with fast straight strokes. When this is dry, it should be sanded with fine sandpaper. The process must be repeated as many times as is required for the surface to begin to gleam. At this time the surface should be sprinkled with very fine pumice and rubbed with a felt pad. (Use just a touch of water to make the pumice a bit pasty.)
With successive coats of shellac, begin to add a few drops of oil to the mixture (use boiled linseed oil or pure olive oil). At this time you should begin to use a circular motion with your cloth.
When old varnish loses its life, it can be revived with strong solvents like crack remover. Crack remover is made with a mixture of solvents such as amyl acetate, acetone, ether and others. The crack remover melts the old finish and revitalizes it. Then you just sand the surface smooth and give it a fresh application of varnish. Remember that all the wax and dirt have to be removed before you use this method.
White spots and rings in varnish can be treated with olive oil mixed with some spirits of camphor. I’ve used this method along with heat on many occasions. You can place an old towel over the affected area and heat it with the iron. This heating causes the moisture to be forced out and helps to force the old gums in the varnish to fuse again. The heat can be reapplied after rubbing with the oil mix to help force some of these oils back in the surface. This type of repair can be finished by polishing the surface with fine pumice stone and polish, followed by rottenstone if you want a deeply burnished finish.
A good mixture to rekindle the finish of varnished pieces can be made using two ounces of turpentine, one ounce of rottenstone and one ounce of linseed oil (raw). Mix all these together and then add one ounce of saturated solution of oxalic acid and one-half ounce of alcohol. This stuff will clean and polish at the same time; it should be rubbed in a circular pattern using a felt pad or something similar.