Acoustic Guitar Strings
Acoustic guitar strings have a long history. Legend has it that Apollo was the first to use strings for musical purposes. He discovered an empty tortoise shell and was inspired to string it and create the original lyre. We’re told the music was heavenly. Mortals being what they are, stole the idea and thus began the long odyssey that has brought us to the guitars of today.
As stringed instruments evolved around the globe, different regions developed different methods for fashioning strings. Strings in the far East evolved from silk and in the Nordic North, horse hair was used. In tropical regions, plant fibers were processed and spun but in the West, we chose the most unlikely material: animal intestines. The earliest examples appeared in several tombs in Thebes discovered in 1823: harps strung with gut strings were found and are said to have still been able to produce a tone after 2,000 years in storage.
Gut strings, despite being inconsistent and rather susceptible to changes in humidity and heat, worked beautifully on short-scaled instruments. The longer the scale, the more difficult the problems of intonation and pitch. The strings could be quite consistent on the scale length of a violin under reasonably high tension. Consistency suffered with length. The longer the scale, the lower the tension. This was fine for unfretted instruments where the player could compensate for intonation problems. Frets are a lot less forgiving.
Without trying to be overly graphic and upset the reader’s delicate sensibilities, the following is a description of the process of making gut strings. If you are a vegan, vegetarian, or easily upset, well, let’s just say that gut strings are made from animal guts and you can skip down to the heading on Steel Strings.
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:
- Animal Slaughter
- Intestine dressing and selection
- String processing and twisting
- 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.
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.
Nylon Guitar Strings
Guitars have a longer scale length than violins but have similar demands on the delicacy and uniformity of the three treble strings. They were designed to be gently plucked as opposed to bowed (like a cello). The frets demanded uniformity to maintain accurate pitch. The three treble strings were traditionally plain gut, while the three bass strings could be made from a silk tread core wrapped with gut.
The company: Albert Augustine Ltd. developed a nylon polymer that had the strength and mass to be suitable for guitar strings. They had the strong advantage of being able to be manufactured within tight gauge tolerances to help assure accurate pitch over the entire fretboard. The three treble strings could be a monofilament of nylon and the 3 bass strings could be a filament core wrapped in silver, copper or bronze wire.
Albert Augustine was a New York instrument builder. According to his wife, Rose Augustine, the material restrictions of World War II made quality metal unavailable for string making. Albert found some nylon line in a Greenwich Village Army Navy Surplus Store and tried it as a guitar string. It worked. Augustine approached the DuPont Company with the idea of string making. They were unconvinced that musicians would accept the sonic qualities of nylon over traditional gut strings. Augustine staged a blind test with DuPont company executives. They happened to select the sound of the nylon strings over traditional gut strings as more pleasing. A new industry was born.
DuPont’s original concern that musicians were a rather traditional group, slow to step outside long standing traditions, turned out to be true. Sales were initially lackluster. Augustine found his big break when the classical guitar virtuoso Andre Segovia discovered the new Augustine strings and became an avid convert. Once the public heard that Segovia loved the new nylon strings, they were fully accepted by classical musicians around the world.
Steel Guitar Strings
In 1858, a patent on the Bessemer process for the mass production of steel from molten pig iron was about to change many things in the brave new world of the industrial revolution. Guitar builders didn’t know it at the time, but their world was about to change as well. Steel offered a uniform, consistent material that could be pulled to very high tension (pitch) without failure. Suddenly, the limiting factor for instruments was no longer strings, but the instruments themselves. Now instruments had to be reinforced to withstand the new tensions created by steel strings. At the turn of the century, Orville Gibson developed the archtop guitar. This new design fastened the strings to the tail block and redistributed all the string force to be downward pressure on the soundboard rather than torsional (trying to rotate the pin bridge up and off the top). The new guitars could take heavy gaged strings and produce louder sounds – even load enough to compete with banjos in brass bands. Once the problem of structural integrity of the soundboards had been solved, the new problem requiring a solution was guitar necks that could withstand the new higher tension strings without warping upward over time. Thaddeus McHugh at the Gibson Guitar Company solved this in 1921 with the development of the steel adjustable truss rod — a threaded steel rod placed in the neck to counter the string tension. It worked.
Following the resolution of the instruments structural issues; players and string manufacturers began to focus upon the evolution of string alloys to produce the most balance, pleasing tone, longest life and most consistent quality. Some of these were developed for electrical guitars and their magnetic pickups, and others are developed for their warm acoustic tonal qualities and long life.
To understand the differences between various types of strings and their alloys, a little history can help.
Steel – Brief Definition and History
Steel is a form of refined wrought iron, the result of removing impurities and creating an alloy of iron and carbon. The carbon content is very small — around .2 to 2.1% by weight. Carbon is the most common choice for an alloy material due to it cheap cost and ready availability. Other alloying materials can be used to develop special qualities of the final steel product — manganese, chromium, vanadium and tungsten. Basically, each alloying material is a hardening agent. The choice is made to determine the hardness, ductility and tensile strength of the resulting steel.
Alloys with a higher carbon content are known as cast iron. They have a lower melting point and therefore lend themselves to being cast into usable products. Alloys of lower carbon allow more uniformity of the material and therefore create more predictable characteristics of the resulting steel products – the kind that are absolutely necessary for the manufacturing of steel musical instrument strings.
The process of extracting iron from ore by heat goes back to the bronze age: approximately 3,300 BCE. Naturally occurring ores of copper and tin were necessary components. Both ores have relatively low melting points. Tin melts at about 250 degrees C and copper at about 1,000 degrees C. As a comparison, cast iron melts at about 1,350 degrees C. In hot liquid form, both can oxidize quickly, so a method was needed to melt the ore in a low-oxygen environment. The result was bronze. The metal was strong and resistant to oxidization (rust). It was an excellent choice for all sorts of tools, weapons and household items as well as art, but not strong enough to be counted on not to break. It was the best available at the time.
Iron ore needed more heat to melt. It was harder to work into tools and it oxidized quickly and easily. In fact, it could rust away in no time at all. But it did have a few special qualities: it was considerably harder than bronze. For this alone, it had great potential as a material of choice for weapons and mechanical devices.
The first step was smelting the iron ore to pig iron. At this stage, it contained too much carbon to be considered steel. The carbon is reduced in subsequent steps and sulphur, nitrogen and phosphorus are also removed (they can make the steel too brittle). The pig iron is re-melted and reprocessed to reduce the carbon to the correct amount.
Other materials can be added at this point:
Nickel or manganese can add tensile strength and stability.
Chromium increases the hardness (and the melting temperature). If more than 11% by weight is added, a hard oxide forms on the metal surface known as stainless steel.
Vanadium increases hardness and reduces the effects of metal fatigue.
Tungsten results in high strength and hardness.
Following the addition of the alloying agents, the hot liquid is cast into ingots or continually cast into slabs. Ingots need to be reheated to be hot rolled into slabs, blooms (used for structural steel for buildings) or billets. Slabs can be cold rolled into sheet metal, but billets are hot or cold rolled into bars, rods and ultimately wires. This is the material that ultimately becomes musical instrument strings.
The process goes through several stages of heating, cooling and working the material. The final stages can include heat treating. The most common are annealing, quenching and tempering.
Annealing reheats the material until it softens, then reworks it.
Quenching rapidly cools the material in oil or water.
Tempering is a modified form of annealing: increasing the surface tension of the final product — hardening and strengthening.
In 1858, Henry Bessemer patented the process for making steel – marking the beginning of the modern era. He was certainly not the first to make steel, but his process enabled steel to be made in large quantities and very inexpensively.
In 1865, the Siemens-Martin process followed: an open hearth furnace capable of reaching the very high temperatures needed to burn the carbon out of the pig iron. The Siemens regenerative furnace had a simple and clever method of using the waste heat from the process end of the furnace to preheat the incoming air. Sir Carl Wilhelm Siemens claimed a 70 to 80% saving on fuel. Most of this type of furnace was closed by the mid 1990s due to the inefficiency of fuel use and a better process becoming available.
In 1875, the Gilchrist-Thomas process was a refinement of the Bessemer process by developing a way to easily remove phosphorus.
In the 1950’s, the Linz-Donawitz process of basic oxygen steel-making rendered the earlier methods obsolete. This method replaced the air blown into the furnace to support combustion with more pure oxygen. The oxygen not only created higher temperatures but limited impurities in the process.
Musical Instruments and Steel Strings
All of these developments were necessary to set the stage for the development of steel musical instrument strings. Once the steel strings were readily available, instrument developments followed to allow stringed instruments to be loud enough to be used for the entertainment of ever larger crowds of music enthusiasts. In the years before electric amplification, the power of the instrument was limited to the ability of the strings to generate enough sound to be heard by more than a small gathering in a silent room. Steel strings made it possible, but the instruments needed to be sufficiently reinforced to be able to withstand the considerable forces of the new strings. Delicate instruments designed to respond well to gut strings were incapable of supporting steel strings without collapsing under the higher tension. New instrument designs were needed.
Banjos responded quickly and performed marvelously with the new strings: loud, cutting and clear tones. Mandolins found new voices as well. The small instruments were easily reinforced for the higher string tension. Guitars, however, were bigger and constructed of thin, delicate materials. If the materials were simply beefed up, the instruments became less responsive – defeating the purpose. The initial answer came from Orville Gibson: a guitar constructed along the lines of a violin or cello. Carved top and back, with the strings firmly held by a steel trapeze supported on the end block. Now all the active force of the strings was directed only downward onto the soundboard. The result was a durable, loud and responsive instrument, well suited to the new steel strings.
Once the instruments were adapted to the available technology, the musicians and the music followed.
The 1920s saw the gradual shift away from banjos and the mandolin orchestras to the guitar. The development of the truss rod in 1921 and the graduated carved tops for archtop guitars that were refined by 1924 allowed the guitars to become the natural choice for the dance music of the era. During the depression years of the 1930s, the music morphed into jazz influenced swing and saw the development of the earliest pickups and instrument amplifiers. The 1940s and World War II saw the height of the Big Bands. The 1950s, following the War, saw the birth of new music forms responding the the readily available and inexpensive guitars that needed an amplifier to make music. The new solid body instruments created a demand for strings that worked primarily with pickups. They had no acoustic qualities, only good electrical characteristics.
Steel, Brass, Bronze – Acoustics and Electrics
The development of guitar strings simultaneously followed 2 distinctly different paths: strings for primarily acoustic instruments and strings for primarily electric instruments.
Acoustic Metal Strings
Acoustic instruments demanded strings with clear, warm tone. Steel strings with steel windings (of just about any alloy) sounded harsh, bright and hard-edged. It was quickly discovered that combining the tensile quality of a steel core wire with windings of bronze yielded strong warm tones and dependable long life. Bronze (used for strings) was a 92% copper, 7% tin & 1% phosphor alloy. This can be expressed as 92/8 phosphor bronze (92/7/1). By adjusting the bronze alloy to 80/20 (80% copper, 20% tin) a slightly brighter tone is achieved. Either alloy suited acoustic instruments and became very popular. The only drawback of bronze alloys is that bronze is not terribly magnetic and therefore doesn’t work well with magnetic pickups.
Ironically, the formulation actually used by many string manufacturers is actually 80% copper and 20% zinc. Technically, this yields brass, not bronze. The zinc is harder than tin (resisting fretware) and doesn’t tarnish as easily – allowing longer string life. The string packages still refer to bronze – go figure.
Widespread use of magnetic pickups in electric guitars in the 1950s led string manufacturers to experiment with alloys having favorable magnetic qualities: Monel steel, #430 stainless steel, chrome, pure nickel, nickel plated steel and any other material they thought might work well. Nickel was found to have a balanced and pleasing tone, it was resistant to fretware and produced very little distortion. Unfortunately, Nickel was hard to come by in the U.S. during the early and mid 1950s so widespread use didn’t occur until after 1956.
In 1954, the German company: Pyramid became the first to offer pure nickel round-wound guitar strings. Pyramid strings became popular with British and European guitarists, but were practically unknown in the United States. By the mid 1960s, however, U.S. made nickel round-wounds such as Fender No. 150 Spanish Guitar and Gibson GE-340 Sonomatic sets were the strings of choice for many English and American rock guitarists, contributing substantially to the characteristic electric guitar tones from that period.
Then, around 1968, manufacturers began advertising strings that utilized stainless steel and various other alloys and by 1970, most were marketing nickel-plated steel round-wound sets in addition to their pure nickel offerings. The primary reason for plating steel with nickel is to reduce fret wear. Nevertheless, Some believe that the change (from pure nickel to nickel plated) was due to higher nickel prices and others feel the change was in response to changing musical tastes.
At the outset of the Korean War, the U.S. government took control of the distribution and allocation of nickel; resulting in a severe shortage for non-defense uses between 1951 and 1957. The result was low supply and high demand – higher prices. Later, the escalation of the Vietnam War led to a steady rise in nickel prices beginning in 1967. Pricing was further affected in 1969 by a series of prolonged labor strikes against Canadian nickel, copper and iron industries. U.S. Geological Survey figures show an increase in nickel prices from $.88 per pound in 1967, to $1.29 in 1970. The cost rose to $2.07 per pound in 1975, and then to $2.96 by the end of the decade.
Some experts say that increased costs were the motive for changing from pure nickel to nickel-plated steel string wrapping containing only about 8% nickel. Others claim that the material content of strings only represents about 20% of the selling price. In any event, most manufacturers continued to offer pure nickel strings while they were marketing newer products.
The music of the 1950s and 1960s underwent massive changes in style and presentation. The new musical styles demanded new and different qualities of string formulations. While pure nickel has a warmth and richness in clean tones; these are not necessarily virtues when you’re looking for raw volume and smooth distortion – demanded by rock musicians during the late 1960s and early 1970s. Increasing the steel content of the windings and also increasing the diameter of the steel wire core, increased pickup output. The resulting hotter signal offered all sorts of new musical possibilities.
In the final analysis, there is no right or wrong choice. The choice of strings is personal – whatever sounds and feels best to the musician.
The primary alloy choices for acoustic qualities are:
- Phosphor Bronze
- 80/20 Bronze
- Silk & Steel
- Coated strings
The primary alloys for electric qualities are:
- Stainless Steel
- Steel-Hybrid (nickel & bronze combinations)
Stainless steel strings (in various alloys) have the advantage of resisting corrosion but the drawback of being a generally softer alloy (wear out faster) and considerably less magnetic (don’t excite the magnetic field of the pickups as well).
Monel is a trademark of the Special Metals Corporation and refers to a series of alloys combining approximately 67% nickel with 32% copper and a bit of iron. These proportions of nickel and copper are found naturally in nickel ore from a Sudbury Ontario mine. The name came from Ambrose Monell, president of Special Metals Corporation and was patented in 1906. One ‘L’ was dropped because family names could not be used for trademarks in Canada at that time. Monel is considerably stronger and more expensive than stainless steel. Because if its strength and resistance to corrosion, it works well for the pistons in valve wind instruments.
Monel was originally used for guitar strings in the 1930s by the Gibson Guitar Corporation. Gibson still uses them for mandolin strings in the Sam Bush signature set. Monel was introduced for electric bass guitar strings in 1962 by Rotosound and became popular with such artists as Sting and John Paul Jones.
Special thanks to Guitar Player Magazine and the following contributers for some of the background material on strings:
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