Guitar Strings - Acoustic Music

How Gut Strings Are Made

Musical instrument strings were traditionally made in the West from the small intestines of sheep. The process breaks down into four basic steps:

1. Animal Slaughter
2. Intestine dressing and selection
3. String processing and twisting
4. String drying and polishing

As you might imagine, the string makers traditionally set up shop next door to the abattoir. There was no time to transport the hot product any great distance. When slaughterhouses were located on the edge or center of a city, in order to be able to transport product to market quickly before refrigeration was an option, string makers followed.

Step 1 – Animal Slaughter

Following the slaughter of the animal, the intestine is immediately pulled while the guts are still hot. The process requires that the blood vessels that connect to the intestine casing be broken off close to the casing wall. If the guts cool, there is a risk that the vessels break a distance from the casing wall and leave ‘whiskers’ that render the material useless for musical instrument strings. The casing is cleaned (of manure) and stripped of fat and then placed in cold running water to preserve its uniform color and strength. There is approximately 30 yards of material in a sheep. Once 5 (+/-) sets are stripped they are bunched and knotted at the center, which makes the long sections easier to handle (when doubled over at the center knot).

Step 2 – Intestine Dressing and Selection

The casings were received by the dresser from the slaughterhouse soaking in cold water. Some dressers would first re-soak them in hot water for an hour or so before machining. All membranes except for the muscle fibers were then removed. This process was called stripping and crushing. It was carried out by scraping the material on a wooden board with a metal blade. It was hard work. The object was to strip off the outer serosa layer and simultaneously crush the inner mucus membrane. The inner membrane, once crushed would be liquid enough to be squeezed out. This was possible by working from the knot downward to squeeze out the mucus from both ends of the long strands at the same time. During the mid 1800s, the process was mechanized and accomplished in 3 stages and rollers. The final result was a clean tube of muscle fiber approximately 30 yards long.

The clean tube was then set onto a sorting table. One end of the tube would be inflated with water – approximately 12″ long and then measured for gauge.

• Narrow – less than or equal to 18mm
• Medium – 18mm to 22mm
• Wide – 20mm to 24mm
• Extra Wide – 23mm +

Intestines vary in diameter over their length. They are wider at the top – for the first 20 yards or so. This is described as the first cut and considered the most valuable section to the dresser. Their main value is for use as sausage casings. It is the second cut – the lower part of the intestines that measures approximately 8 to 15 yards that is best for strings. The major purpose of the upper section of intestines is to constrict around and pulverize the food entering from the stomach. As a consequence, the muscle fibers of the upper intestines are shorter and oriented around the tubes. Further down the line, the muscle sections lengthen and orient along the path of travel to help move the food. These longer fibers make better strings.

Back to the water injected into the tubes: As the water is moved through the entire tube, it is checked for consistency and quality. If large holes are found it is cut at those locations. Once sorted for gauge, quality and length, they are grouped into ‘Hanks’. Each Hank is made up of about 100 yards of material and stored semi-dry in a special salt solution in barrels until they are ready for further processing.

Step 3 – String Processing and Twisting

The String Maker then takes and rehydrates the Hanks and rinses out all the salt with some form of alkaline solution (this varied over time and by region). The tubes are then cut in half (or more sections) along their length. The purpose is to separate the fibers into evenly stressed ribbons. The ribbons are then separated into smooth side (or ‘rights’) and rough side (or ‘lefts’). The smooth sides are a bit more pure and suitable for the treble strings. The rough side usually ends up as the larger diameter strings.

Following splitting, the ribbons are ready to be cut to length and processed into strings. The standard lengths could be 84″ and 55″ for twisting.

The next four days are used to ferment the gut. The gut has natural enzymes that are activated by an alkaline solution and heat. With careful monitoring, frequent water changes and daily scraping, the oils and fats break down and leave a pure fibrous collagen structure. The result is uniform white ribbons. To achieve an even more uniform color, the ribbons are then bleached either with sulfur fumes or hydrogen peroxide.

The strands are then twisted into strings. The number of strands determines the string gauge.

String	Ribbons	Side
Violin E	3	right
Violin A	8	right
Violin D	15	right
Viola A	8	right
Viola D	15	right
Cello A	24	right
Cello D	15	left
Bass G	21	left
Bass D	38	left
Bass A	64	left

The Art of string making is in the process of twisting the strings. The bundle of ribbons is combed and twisted without tension to achieve a twist angle of about 17 degrees. Each string maker has their own special method to control the twist angle. The ratio of the ‘swing’ angle (the sag of the bundle during twisting) to the string length and diameter is proprietary to each shop. For the first 2 or 3 days, the string needs to be tightened several times as the water evaporates and the string stretches. Over these few days, the string settles in and becomes stable. The drying process takes 2 to 4 weeks as the strings season. The object is to allow it to happen slowly.

Step 4 – String Polishing

Once properly seasoned, the strings could be polished. The concept is to create a string of uniform diameter and mass. The mass would be determined by the process up to polishing. The polishing then would essentially sand the string to a uniform diameter. The process might remove 20% of the string over its length. This implies that there has to be enough diameter to start with to achieve the final desired gauge.