Monthly Archives: October 2015

Why Hide Glue?

This is far and away the most common question posed by my colleagues in India. Allow me to
preface this long and somewhat technical article with a comparison of your violin to your car. If you take your prized automobile to the shop to have the oil changed and new spark plugs installed along with a tune up, think how upset you might be to discover that the hood (British English: “Bonnet”) been judiciously welded shut to keep it from opening so easily. I think the owner might agree with me that this might lead to a far more extensive and costly repair the next time your vehicle needs an oil change. The violin family instruments also require access to the interior of the instrument in order to carry out various repairs.

During the first course of instruction in Chennai, I insisted that we would be exclusively using hide glue, also known as “animal glue,” or in Hindi “sarres.” This announcement caused quite a controversy, with the professional instrument repair persons among the participants complaining loudly that our work would fall apart before the clients were out the door. They felt that their good work would be rejected by their clients if it became known that hide glue had been used in their instruments. My response to that was: “You’ll just have to educate them.” And the entire violin playing population of India, as well… big job! For this reason, it is our hope that every player of violin, viola, or cello in India will read this and carefully consider the implications for their own instrument. It may help the player preserve the beauty and integrity of their violin and pass it on to their heirs in reasonably preserved condition. After all, your violin will long outlive you, as long as it is well cared for during your short tenure as caretaker.

It is largely true that imperfect joinery in our woodworking project can cause hide glue to fail, in particular in violin family instruments because they are subjected to prolonged vibrational stresses, often at the hands of muscular, vigorous players. It’s amazing to me that some players don’t just break the instrument in half from the force of their bowing. Hide glue bonds best when the wood joinery fits together perfectly. That is the reason the main focus of our first course in Chennai was not only on issues of set up and adjusting the instrument for ease of playing and maximum tone production, but also sharpening our tools to a razor keen edge and practicing cutting wood to the perfection required of our trade. India has a magnificent tradition of fine art carving in wood, and our students demonstrated all the patience of that grand tradition when we called upon them to cut a new sound post into an instrument. They spent the better part of one week cutting away at the end of a piece of 6 mm spruce soundpost dowel with a knife (no files, no sandpaper) until it fit perfectly to the interior of the violin in the proper position for tone production. This same fastidious approach applies to every glue joint in the entire violin.

It is true that hide glue can fail if subjected to radical humidity change, in particular if the unvarnished project is exposed to dry conditions and the wood shrinks away from the joint. This can be handily re-glued and the wood typically becomes more stable once varnished, largely eliminating the problem. This characteristic also allows your violin to open a seam rather than crack a plate, literally the safety valve of your violin. Fortunately, I saw little of this type of damage in India, since it is exposure to very dry conditions which causes most cracks in the plates, with the exception of accidents. If the violin is dropped or otherwise suffers a shock, it is much more likely to simply come apart without damage when joined with hide glue, allowing an easy re-gluing. I experienced this first hand when our friend dropped my violin on the asphalt road in Mahaballipuram and the neck popped out of the body without even the most minuscule splintering of the wood. While it looked broken to the untrained observer, it took me longer to calm our friend’s frayed nerves than it did to re-assemble the violin, about 15 minutes. Synthetic resin glues will not function in this manner. After all, they famously proclaim on
the container that the workpiece will never come unglued. So breakage is often the result
in such a situation, and a very costly and time consuming repair is often necessary.

Players frequently travel great distances in the course of performing, so the violin is also routinely exposed to radical changes in climate and humidity. The varnish is the main defense against the wood in your violin shrinking or expanding too quickly. Nonetheless, violinists have often had the traumatic experience of discovering an area of their instrument coming open, resulting in an irritating rattling noise emitting from their beloved instrument alongside the glorious tone to which they are accustomed. Perhaps the fingerboard might fall off during the concert. The neck might even separate from the body. Never fear! The violin is supposed to do exactly that when subjected to these stresses. A common mistake under such circumstances is to panic and resort to a quick fix with a synthetic resin glue or some other objectionable adhesive, generally resulting in more damage to the instrument when the job needs to be redone later by a professional violin restorer. A better course of action in an emergency situation would be to borrow an instrument if possible, or struggle through the performance and bring the violin to a professional shop as soon as possible for proper reassembly. Such small problems, however traumatic they may seem at the time, are routine maintenance issues for the skilled violin technician and usually not so costly.

We need to be able to dismantle the instrument entirely with minimal harm during the course of many repairs, since we don’t have the convenience of just reaching our hand and tools into the body through the sound holes like our fortunate colleagues in the guitar industry. If necessary, I could dismantle my own violin completely and cleanly in approximately 15-20 minutes. If a synthetic resin glue like Fevicol or Titebond aliphatic resin glue is used, the glue bond is literally stronger than the wood itself, so the likelihood becomes greater of causing more damage to the violin during repair, resulting in unexpected higher cost to the client and unlimited possibilities for aggravation to the repair technician. Unfortunately, with hide glue the instrument can indeed come apart a bit here and there, much to the dismay of the player. This is not a capitalist ploy to keep you returning to the repair shop. Rather, it is the “safety valve” effect of the hide glue releasing the joint when the wood shrinks and expands.

Hide glue is the only truly time tested glue for violin family instruments. There are numerous examples of hide glue joinery in instruments that are hundreds of years old, yet never failed… yes, even in the harsh, humid climate of South India. Glue joint failure is not uncommon in violins repaired with synthetic resin glues, but cleaning this substance out of cracks or the joinery can be a difficult time consuming process, often requiring cutting or patiently picking it out, possibly resulting in further damage. Hide glue is easily cleaned out of old repairs using nothing but water. It will not bond to synthetic resin glue, so the cleaning process during repair is of utmost importance. Hide glue will bond to old hide glue, a very useful characteristic. Furthermore, hide glue literally pulls the wood parts more tightly together as it dries, leaving very little of the protein bond in the joint, resulting in the near invisible joinery that we admire in classic violin making and restoration. Furthermore, this characteristic allows us to assemble many projects without clamping. Some violin makers join the plates (center joint) on their top and back plates by simply rubbing the two pieces together until they feel the glue start to set, then carefully set the piece aside without clamps until dry. This joint can withstand all the stress of string tension and bow pressure of the player without failure, even though carved out to a thickness of as little as 3 mm.

Hide glue can even be used as a sealer on wood to prevent stain and varnish from inappropriately penetrating the wood and causing uncontrollable negative visual effects. A refined cousin of hide glue, gelatin, is commonly used as a sealer coat on the entire instrument before application of varnish. It’s the one I use on my instruments. This is a closely guarded ancient secret, so please keep it to yourself.

As a vegetarian myself, I’ll admit that I don’t much care to think about the processes involved in the manufacture of hide glue, which involves rendering tissues from dead animals. If not somehow kept perfectly dry, the sub-tropical climate of South India can soon make your supply of hide glue reek horribly of putrefaction, at which point it might be better discarded and a fresh supply procured. However, despite the fact that hide glue has fallen out of favor with many woodworkers in modern times, it stands out as a miraculous substance with many applications, a boon to all of violin making and restoration. I and most of my colleagues in the trade use it exclusively. In our violin specific application in the adverse climate of India, I nonetheless believe that it is worth overlooking some of the perceived shortcomings of hide glue in order to
ensure the preservation of violin family instruments for future generations to enjoy.

Many more are the uses of this wonder substance passed down to us from antiquity, too many to list here. I have even on occasion made jokes about the violin maker being able to eat hide glue for protein source if overtaken by tough financial times. That is, until I heard tales of one of my highly regarded colleagues from the Polish tradition, who cleans off the squeeze-out from his violin joinery by lapping up the excess glue with his tongue, much to the amusement of his co-workers. Given my personal dietary inclinations, I’ll not be testing this application any time soon, thanks.