Sunday, February 2nd, 2014
The repair of a crack in the top or back of a violin is very delicate. It should only be attempted by a competent violin Luthier. We assume NO responsibility for any damages resulting from anyone following the advise of this article. The advice in this article is based on the teachings of Master-Luthier Henry Strobel senior.
First make sure that there is no wood missing in the break and it can be glued back together. If you apply gentle pressure( DON’T break anything) on both sides of the crack, make sure that the wood grains line up and there are no gaps. Check the insides of the crack to make sure both sides are totally clean from dirt, oils, adhesives, rosins, oxidation, waxes and different glues. Any residue will prevent you from concealing the crack and possibly from successful gluing.
Every cleaning agent has some side effect. It may swell the wood, ruin the existing varnish, prevent the glue from holding, or cause a weaker bond that will open down the road. You should use the weakest of these agents (that will do the job) sparingly and remove any excess ASAP.
If you find dirt or oils in the crack try washing it out with very warm water on a thin medium short stiff haired brush (or q-tip). Water may swell the surrounding wood or even warp it. Sometimes you may need to remove the violin top/back in order to open/move the crack sufficiently to allow for proper cleaning. It may be advisable to put temporary cleats at the ends of the crack inside the violin to prevent the crack from spreading further.
Alcohol can be used to clean polish, rosin and varnish out of a crack. It evaporates quickly (no swelling) but it may adversely affect the varnish around the crack.
Carpet spot cleaner is a good household product to clean the crack. It should be diluted with water as much as possible and will remove proteins (hide glue). It is relatively safe but may however affect the varnish. Be careful how you use it.
Oxalic Acid is also used to clean and bleach cracks. It may have a residual effect on gluing. Chlorine Bleach and Hydrogen Peroxide are also used to bleach stains.
Some of these chemicals are very dangerous to use and may cause foaming reactions. Mixing cleaning agents can be a disaster. Know your chemicals before you start! You don’t want to produce a fire, poisonous gas, or destroy the instrument finish.
To be continued in Part II.
