Historically informed?

Are the gut strings used in HIP really true to those used by 18th- and 19th-century players? Kai Köpp examines the technical reasons why today’s strings might sound quite different from their predecessors

Points of interest to violin and bow makers

Dried cow gut (left) and sheep gut (right) have very different physical properties

Playing on gut strings has become increasingly popular among today’s string players. Animal intestines are used not only as the core of a wound string, but also unwound – for example on the harp, and of course on all stringed instruments in historically informed performance practice of Baroque, Classical, Romantic and even early 20th-century modernist repertoire.

However, with very few exceptions, beef intestine is used for making gut strings today, even though it is much too large for the production of fine strings.Before the 1970s good gut strings were traditionally made from sheep intestines, and the change to beef gut required new techniques and chemical processes. It seemed necessary due to a shortage of materials, but also for economic reasons – since the consumption of sausage products has increased worldwide, the entire provision of high-quality sheep casings today is absorbed by the sausage industry. Also, because the large-calibre beef intestine cannot be processed into sausage products, it is cheaper by far than sheep intestines. But these new beef gut strings have noticeably different playing characteristics from sheep gut strings.

THE BEEF GUT STRING AVAILABLE TODAY IS GENERALLY DIFFERENT FROM ALL HISTORICAL STRINGS

First of all, the difference between sheep and cattle is not only related to the size of the animal and the intestine, but is particularly evident in the different structure of the intestinal walls. In sheep intestines, only the connective tissue (submucosa), which is separated from the outer skin of the intestine by muscle, is suitable for making strings. This fine, tubular material, which detaches itself from the rest of the intestine through natural decomposition processes, has a high degree of elasticity thanks to the cross-lattice design of its fibres. On the other hand, bovine intestines have a leather-like outer skin (serosa), which is only very slightly elastic. The submucosa of cow gut is much more fleshy than in sheep, and is also more prone to rotting. Obviously the different physical properties of submucosa and serosa will have a direct effect on the tonal and tangible properties of anything produced from them, and elastic sheep gut strings will have clear advantages over the stiffer cow gut strings in controlling the vibration under the bow.

Layers of the gastrointestinal tract with outer skin (serosa) and connective tissue (submucosa)

But even the use of submucosa will not guarantee a string that comes close to the historical playing characteristics. Naturally, the manufacturing process will also play a decisive role. In the German string making tradition, the cleaned and wet sheep gut tubes were split lengthways into two parts, to compensate for tensions in the material caused by the natural twisting of the raw intestine.Strands were assembled from these wet parts, and twisted at a specific angle of rotation (see ‘Song of the gut string makers’, The Strad, April 2021). While they were slowly drying on a frame, they got a few extra turns if necessary. An experienced string maker could even predict the later diameter and playing characteristics of a dried string based on the composition of the raw material. The exact composition of the wet parts required a great deal of experience and specialist craftsmanship, which has not yet been reproducible by machines.

A centreless grinder provides cylindrical shapes for strings of both cow or sheep gut

GRINDER PHOTO WILHELM GEIPEL

In order for the finished string to vibrate without interference, it must be as cylindrical as possible.However, a twisted string made from natural material often shows very small deviations in diameter and therefore does not always produce pure tones.Until after the First World War it was customary to cut out the most even sections from a string several metres long, so that only the best sections would be used on the instrument.

But such material-related imponderables in quality assurance are hardly acceptable for an industrial product. Therefore, in the 1970s, a new technology was introduced that would make a workpiece perfectly cylindrical from the outside – the so-called ‘centreless’ grinder. This technology, which produces any desired diameter, cuts through all the outer fibres of a twisted string made of natural gut. As a result, the string loses the natural cohesion of its surface and thus part of its tear strength and its resistance to abrasion and hand perspiration. This accelerates wear and fraying – regardless of using sheep or beef gut. Sometimes this is counteracted by the addition of natural or artificial adhesives such as collagen, or even polyurethane in the case of ‘varnished gut strings’ as they are known. This only adds to the stiffness of modern products. The naturally less elastic bovine serosa, on the other hand, dries into a bumpy cord which can only be processed into a cylindrical string, thanks to this innovative manufacturing technique. Traditional strings are rougher because they are not polished, so the outer fibres remain intact. This rough surface provides ideal contact with the horsehair of the bow.

Consequently, the beef gut string available today generally differs from all historical strings in three ways. Beef intestine is used instead of sheep gut; instead of elastic tubes made of sheep submucosa, solid strips of bovine serosa are processed; and finally, the string may be artificially glued to compensate for the loss of stability caused by the cylindrical grinding. Especially in the field of historically informed performance practice, this means a hardly acceptable deviation from the original product and its characteristic playing properties – especially since the physical differences are also clearly noticeable in terms of sound and feel, as experiments have shown.

These disadvantages come at the price of the string manufacturer’s ability to offer exactly cylindrical diameters in hundredths of a millimetre. While such reliability has never been available in music history, it seems questionable whether this innovation really serves the cause. Hand-crafted strings made from sheep intestine are preferable in terms of elasticity, sound quality and durability, even if their production is inevitably more complex than the modern industrial product.