Fundamentally, acoustic guitar strings have been around longer than any other type of guitar string. They have evolved into one of the most critical components of the acoustic scene. Technology has taken the tone capabilities of the acoustic guitar string to new levels. There are many choices, sometimes leaving musicians confused at times. We are going to discuss one aspect of acoustic guitar strings in this writing…Metal.It’s about metal…What makes an acoustic guitar string different than electric guitar strings? Metal. Electric guitar strings utilize ferromagnetic metals, namely steel, to allow the pickup to sense it. Electric guitar pickups are based on variable reluctance technology. They rely on a magnetic field to be interrupted by a metal target (aka. Guitar string). The interruption is in the form of a vibration from the string. Acoustic guitar strings do not need ferromagnetic metals. Amplification is often not a focus of the acoustic guitar. Strings with clarity, brilliance and volume are preferred. The technology used to amplify an acoustic guitar does not rely upon strings having ferromagnetic properties. Transducing an acoustic guitar is more about picking up a signal via piezo effects, or sound pressure being picked up by a microphone. This opens up the door to a wider variety of string selections.There are many different flavors that acoustic guitar strings come in these days. A series of alloys exist at the most basic level. Interestingly, I find players of all ages and experience who do not know the differences in string metals. Some have a rough idea, while some have no idea. Copper, zinc and tin are metals seldom discussed by guitarist. As soon as a number like 92/8 or 80/20 is mentioned in reference to alloy sets, bewilderment can start. If you are thinking, “Yeah, what the hell do those numbers mean to my tone?” You are about to find out. So, without further delay, here is a guided tour!The Acoustic String Metal GuideBronze – Of all the strings manufactured, bronze has got to be the brightest and most articulate string available. There are no strings that are “pure” bronze, per say, but a mix of several different alloys including tin-phosphor, zinc and copper. The core is usually made of steel. Bronze strings can make virtually any acoustic guitar come alive with highly penetrating tone, versus their steel string counterparts. Bronze metal is known for its shimmer and brassy sound, but a deep rich low end can also be attained. Since string coatings have become popular, many of the previously highly corrosive bronze sets have become popular again. Uncoated bronze sets can lose their brilliance after a few hours of playing, as they can be highly corrosive. Many players used to use them for recording sessions for their short lived brassy sound. String coatings in general, have pumped new life into acoustic bronze sets. The brassy sound can last for many weeks, or months, without decaying.80/20 Bronze – Here is one of those numbers we mentioned earlier. What does 80/20 mean? It is the ratio of copper to zinc in the wrap wire. The wrap wire is 80% copper while the other 20% is zinc. Since copper is highly corrosive, the zinc component helps slows down the aging process and adds additional hardness. However, since the advent of string coatings, the corrosion issue has all but disappeared as a primary concern. Although, poorly coated 80/20 strings, or strings with worn away coating will corrode. Tone wise, the 80/20 mix is excellent for creating a string that yields fantastic tonal range. The 80/20 strings are known for their brilliance and crisp highs. Uncoated versions of this string can lose brilliance after a few hours of playing sessions. In fact, this string has gotten a bad rap over the years for being “dead” sounding due to its high corrosion rate. Super old sets exposed to high humidity can turn light green from the copper content. Again, coating technologies have completely changed this factor.85/15 Bronze – This string has a tonal spectrum in between an 80/20 bronze and a phosphor bronze string. It retains much of the brilliance found in an 80/20 bronze but captures the warmth and fullness of phosphor bronze strings. The 85/15 was the initial development of the more popular 80/20. However, 85/15 still remains a popular choice for finger style playing. It helps add volume to finger style articulation and give clarity similar to a plectrum.Phosphor Bronze – The phosphor bronze strings were developed to have a longer lasting life cycle. In other words, the phosphorus content helped preserve the brilliant tone longer than the 80/20 and 80/15 bronze strings. Phosphor bronze strings are the darkest sounding of the bronze string family. They have about 75-80% the brilliance of a fresh set of 80/20 bronze. Phosphor adds a warm pleasing tone that give a tonal softness not found in other strings. They tend to have a little less “pick noise” as a plectrum sweeps across the strings. In fact, some sets have been known to yield a soft “brushing” type of pick noise.92/8 Phosphor Bronze – The 92/8 is a ratio represents a blend of 92% copper and 8% tin phosphide in the wrap wire. The 8% actually breakdown to a 7% tin and 1% phosphor composition. The tin phosphide helps preserve the tonal range over time. Again, since the advent of coatings, the role of phosphor in coated string is purely tone versus longevity.Gold Plated – In an effort to prevent corrosion, some strings utilize a micro layer of gold plating on the wrap wire. The gold plating gives a less brighter sound than the non-plated 80/20 bronze string sets and non-plated phosphor bronze sets. The gold is often plated on 80/20 bronze wrap wire and phosphor bronze sets. The gold plating is a good alternative for players who feel the poly-resin coating on strings impact string performance.Titanium – Acoustic string sets based on titanium compositions and cores have been cited for their corrosion resistance abilities. The non-ferromagnetic properties of titanium strings inherently put them in the acoustic class of strings. The tonal range of titanium is somewhere between steel and bronze sets with a very unique sounding clarity and richness. Titanium is a bit of an exotic metal and can be over thirty times the cost of stainless steel.Stainless Steel – Stainless steel strings bring their own tonal uniqueness to the acoustic world. Their high tension requirements make them less friendly to acoustic designs, but still give exceptional performance. Steel give a much softer sound with less volume than their bronze counterparts. They make a good choice for the hard strumming, open style chord players. Players on a budget will appreciate their availability in low price points. In addition, their stainless properties give them good corrosion resistance.Silk Steel – Don’t own a classical guitar? No problem. For players seeking the soft sound of classical guitar strings, silk steel strings deliver the classical tonal range. This string is constructed of a center wrap of silk with a steel winding. The combination of silk and steel bring a classical tone to finger-style players wanting to keep their traditional dreadnaught or concert auditorium acoustic guitar. Unlike classical strings, the silk steel strings come with a ball end to anchor in a bridge made for metal strings.We have covered a lot of ground here. As you can see, there are a bunch of options for alloys in the acoustic string world. Hopefully, this overview has provided enough insight to let you know the differences between the various alloys.