Cleaning and French polishing a Violin
If you are going to be retouching a violin, French polishing it or working on major repairs such as crack repairs a thorough cleaning must take place first.
To achieve a proper cleaning will will have to use different types of chemicals. You should avoid any type of rubbing compound or abrasive cleaners. The one thing I can't stress enough is to avoid the use of furniture polish of any type, including Old English Scratch remover. A lot of furniture polishes contain silicon, which can work it's way through a finish or open crack and hamper repairs or touching up of the instrument. One of the best solvents in cleaning violin rosin is called Xylene. You should be able to obtain this from most good hardware stores . Now let me warn you Xylene is very dangerous ! The fumes are very toxic and the liquid can enter through the skin and cause damage to internal organs. So if you use it you must were gloves and be in a well ventilated room or preferably outside. Also be aware that Xylene can damage certain types of varnish.
It would be wise to test any type of solvent before using it on the main body of the instrument.
A good place to test it would be under the chin rest or under the tailpiece after removal. If it is an inexpensive student instrument most likely the Xylene will not affect it, but check first.
A good cleaning agent you can use is Mr. Clean straight out of the bottle. Keep in mind that this is mostly to remove plain dirt and grime and will not have much effect on rosin.
One other product that will work is Naphtha. It is normally used to thin down oil-based paint, enamel and varnish. As with all cleaners - Do a test first to avoid varnish damage. Use gloves and be well ventilated room. Try to keep this or any other cleaner out of a open crack. This could impede a proper crack repair.
Basically I just use paper towels with Mr Clean or Xylene. Pour a little bit on the paper towel and start rubbing on the dirty areas of the instrument. You will find that the most build up of rosin is around the bridge area, end of fingerboard and around the "C" bouts, because of the rosin coming off the bow when playing. Dirt gets built up on the upper rib, back and fingerboard. This occurs when the players hand slides to reach the upper position of the neck. If it hasn't been cleaned in a while there can be a lot of dirt built up and will need repeated effort to clean it properly. Try to avoid any cracks when cleaning because the dirt from the paper towel can become logged in the crack.
If you still can't get the violin cleaned there is a possibility that the dirt has become embedded in the varnish. If the varnish is very thick and with little chance of removing any coloring you could use some mild abrasive cleaners at this point. On expensive violins a protective coat of varnish is applied over the original varnish. This outer layer of varnish is not usually affected by the Xylene, but the original varnish may be, so be careful.
After you have finished cleaning the instrument you are ready to touch up worn areas, repair cracks or start French polishing. The type of French polishing on violins is different then the technique used to build finish on furniture or guitars. On a violin it is used to resurrect an old worn out finish or to blend in a repair area.
The materials need for this is: lint-free linen sheeting, mineral oil and ethyl alcohol. you can take a 13 cm square and fold it into thirds and place in between your fingers as in the pictures shown at the start of this article. I personally find it hard on fingers that way so I bunch the square into a ball shaped pad. Now you will need to soak the cloth in alcohol, but do not let it become dripping wet, then add a couple of drops of mineral oil on the cloth were it will make contact with the violin. This is going to be the hard part. You don't want the cloth too wet or it will eat through the finish. If it is too dry it will not soften the the varnish enough to move it around. That is something you will gain from experience. I strongly suggest you practice on cheap junk violins to gain this experience.
As you start the polishing move in a 10cm circular motion. Start with a very light pressure and continue to ad more as you see how the alcohol is affecting the varnish. Do not stop this motion or you will leave an imprint of the cloth on the varnish. If you start to mess up keep rubbing until the alcohol evaporates. After the alcohol dries up ad more with a few more drops of mineral oil. Continue this procedure till the instrument is completely polished. Don't use the same area of the cloth for too long or you will get oil build up, which will then get deposited on the instrument. Move the cloth around to a different area. It is a good idea to try this first on the back of the violin to gain the necessary skills then proceed to the more delicate top . Be careful of the pressure you are using around the f-holes and the lower larger areas of the top the are very susceptible to cracking.
At times you will will have a varnish that is so worn and dried out that it need more than just an alcohol French polish. In this case I will use a french polish formula. The technique is still the same as the alcohol method except we will use a French polish made with De-waxed orange shellac flakes and Benzoin. First dissolve the gum resins in alcohol then use two parts Benzoin solution to one part orange shellac I mix them in separate jars first and then mix them together. It is hard to tell when the shellac is dissolved so that is why I mix them separately. Thin this mixture out into a very thin solution. Put some on your cloth with a drop of oil and polish in the same way as before.
You can make a French polish with just shellac flakes but the added Benzoin makes for a more robust formula.
After you have finished you should use a good violin cream polish to complete the process.