THE CURVE

As already announced, this week we start  dealing  with one out of two of the most important aspects in the bow: “the curve”. there are only two kinds of curve in bow-making: those that are properly done and those that are done in a wrong way.

What I wish to say is that, in fact, there are many curve models: Tourte, Peccatte, Vuillaume, Sartory, just to name a few. All these curve models work, in both mechanically and acoustically meaning,  in a complete different way. A bowmaker can easily choose one or the other, basing his work on his own sensations and concepts depending on his own heritage of experience. Nevertheless every curve should be carried out in a perfect way so that the bow can play in a  correct way. Speaking about bows, the topic “curve” is one of the most important and widest one, for this reason we will go on with further explanations in several steps. This week we will speak about one of the biggest problem, often without solution: the “ curve flattening  ”

The word “flat”, if you carefully think about it, is the exact antithesis of the bow. The only straight line is the hair, no else. This flat line is the result of the curve of the stick in tension, that means that every tension changing slightly modify the mechanical working of a bow. If you stretch the hair a lot, the stick will become more “nervous” and will “dance” more; if you release it, the stick will become smoother and easy to handle. When the curve is properly done and the stick releases under the movement of the hair in a homogenous way – as in the picture # 1 – the bow will have a complete adherence from frog to head without any slackening. On thecontrary, if due to lack of competence or wear, the bow shows flat points –  picture # 2– these imperfections will directly affect the tightness of the bow on the string and consequently on the sound itself.

When, while playing, one reaches the critical point, the sudden change of tension will cause an immediate lost of adherence on the string, thus affecting the sound output.  It is very important to detect this imperfection, because in comparison with direction and torsion defects that can be removed, it is very difficult, even almost impossible to solve and remove it. The reason is a very simple one. The bow has no strong side tensions, they are all in the vertical direction.In the curve, the strengths pay a major role and are in  strict connection with the thicknesses. It goes without saying that if the bowmaker has removed too much wood in a specific part of the stick, the thicknesses will not be able to cope with the strengths they  are required to sustain and the bow structure will be permanently compromised. The curve defects can be found also in ancient author bows, in this case they occur because of the wear and prolonged use. We use to say therefore that the bows are “out of fiber” and in this case as well , impossible to be recovered.

In order to see if a curve has been properly done, it is necessary to stretch the hair by means of the screw, beyond the normal playing tension; in this way any possible defect will appear more evident.   After this first inspection, stand in front of a white background so to create a contrast and place the bow at eye level with the frog horizontally in relation with the floor, as you can see in the opening picture.      

(Caution: in the picture I stretch the hair with my left hand in order to watch them more carefully, but this operative check is very dangerous and should be carried out only by an expert ).

Watching the stick in this way, if the curve has been properly done,  you should see how the stick stretches smoothly without sharp corners throughout its length from frog to tip.

We stop here by now but the topic is far from being exhausted here. Next week we will speak about the relation existing between the curve and the bow strength.

So long

Paolo