In this section, I will hopefully be able to describe the materials and processes in a way that will help to clarify some information that has become very confusing for a number of reasons.
Guitar pickups in their simplest explanation are copper wire wrapped around magnets, keep this thought close and you'll be served well!
Alnico, which is an acronym for ALuminum, Nickel and CObalt is the Iron alloy that our pickup magnets are made from. The magnets come in three different strengths, based on their magnetic pull, from strongest to weakest they are: Alnico 5 which is, by far, the most commonly used magnet today. Alnico 5 can be described as having a "Punchy" and "Dynamic" sound, as well as helping to create a tone that lends itself to being more supportive of "Highs". Alnico 2 is what would be considered the middle strength magnet, Alnico 2 is considered "Warm" , with what is often referred to as a " Round " tone referring to a balanced tone with a lot of Midrange response, and a diminished High and a less "Piercing" sound. Alnico 3 is the weakest of the three, I know you're probably thinking, HA!, he made a mistake, nope, somebody decided, somewhere along the way that it would go strongest, Alnico 5, Alnico 2, and then Alnico 3, stupid but true. Alnico 3 Is described as having a very "Bell" like, "Chimey" sound and was also the magnet of choice by Fender in 1954 and 1955 for the first two years of the Stratocaster.
The magnets are also available in different lengths for pickups, this was to compensate for a very round neck or a " Vintage" neck radius, which is much less commonly used today. When you couple the lower strength magnet and "Round" neck were the reasons Fender went with what is called a "Staggered pole" configuration on their pickups in the early years of the Stratocaster, but not the Telecaster. The use of Staggered pole pickups in today's pickup industry is considered mostly for the purpose of tradition and to be "Vintage Correct". Most now agree that a "Flat"or "Flush pole " configuration creates a more even tonal distribution and creates better string separation, however most people still choose the staggered pole, apparently to comply with tradition, because it's not for the tone.
Magnets are shipped in larger quantities to pickup builders "Uncharged", meaning they aren't magnetic yet. Large magnets or large quantities of magnets would create bedlam in the Post Office or on a UPS truck, so "charging" them is one step in the process, normally done after winding and before wax potting. The direction of the charging (North or South) is called the Polarity, the significance of this step is that the magnets can be charged North aka North up, Or South, aka South up, the pickups will perform a certain way when paired or played with another pickup simultaneously when the pickups are both charged in the same way and will perform differently when the pickups are charged opposite, see the "RW/RP" paragraph for more info on this. There also is no, I repeat, no, industry standard in reference to charging/polarity.
With the exception of the neck pickup in a a Telecaster, all pickups are wound with Copper 42AWG wire , which is the gauge or thickness of the wire. The wire that is wound onto pickups is about the same diameter of human hair and is even more fragile than human hair. An average number is about 8,000 winds around the pickup bobbin to make one pickup. The wire also has one of three different insulation coatings on the outside to keep it from shorting itself out, however, it does not change the wire itself, just the insulation coating. The most commonly used today is called Polyester coated, it's very durable in comparison to the "Vintage" used wires. The most common "Vintage correct" wire is called Formvar, an acronym for Formulated Varnish which, again, only references the insulation type, as the wire is all the same. The third and least used is called "PE", which stands for "Plain Enamel", again just the insulation. Many people swear that they can hear the difference, I can't, electrical engineers state that the insulation has no influence on the electrical signal. This isn't an argument, merely an observation, if for the sake of being "Vintage Correct" people want it made that way, I'll make it that way. When the wire Is being wound onto the bobbin , it can be either wound clockwise (CW) or counter clockwise (CCW), see more about this in the "RW/RP" paragraph. The winding process is a very critical step in the pickup building process, if it's wound too tight, it will break, over and over and over, each time it breaks , you have to cut all of the wire off and start again, some people will solder it and keep on going ,in my opinion leaving a very weak link, I wouldn't do that on my pickup, I won't do it on yours, period. If the coil (as the wire builds up it becomes a "coil") is wound too loose, you will have wire possibly hanging off of the spool, another weak link, the pickup will very likely be excessively "Microphonic", this Is when the coil vibrates from the electrical signal and it begins to pick up ambient sound, more guitar body wood influence, more bridge plate influence and even outside sounds, some are bad enough that you can yell into the pickups and hear it as though it was a microphone, hence the term "Microphonic". Older guitars will become slightly or sometimes even more moderately Microphonic and this can, to some player, as a matter of taste, be desirable. Loose coils are suspect for completely falling apart, especially, before installation, even more so before wax potting. So a pickup too tight keeps breaking, too loose is going to be Microphonic or worse, fall apart. A coil that is nice and tight, and has been evenly wound onto the bobbin Is likely to perform for many years to come, singing beautifully! Without saying too much, I'll say this, winding tension is what separates the men from the boys.
Reverse Winding/ Reverse Polarity (RW/RP)
Single pole (Stratocaster and Telecaster style) pickups are known for their 60 cycle hum, this is an audio interference that is particularity aggravated by the presence of fluorescent lighting, neon lighting, ceiling fans and dimmer switches. Hum canceling or hum bucking pickups address this problem. Hum canceling is accomplished by winding two individual pickup coils in opposite directions (one clockwise and one counter clockwise) additionally, the magnets are charged opposite with reverse polarity, one North, or North up and one South or South up. If desired hum cancel can be achieved on a two pickup guitar like a Telecaster by using an RW/RP setup, on a two pickup guitar this is done by winding the two pickups in RW/RP in relation to each other, it doesn't matter which is clockwise or counter clockwise or north up and south up, they just need to be opposite. To use this function the middle switch is selected it will send power to both pickups, but with hum will cancel and a very slight drop in signal strength will occur. On a Stratocaster there are five possible pickup combinations selectable by the 5 way switch. The first position, being the lever furthest down is the bridge pickup alone, second is a mix of bridge and middle pickup, third is the middle pickup alone, fourth is a mix of middle and neck pickup, fifth is neck pickup alone. The only positions that are pertinent to the RW/RP are the second and fourth, when two pickups are mixed. On a three pickup guitar like a Stratocaster, this is achieved by the neck and bridge pickup being wound identically in terms of wind direction and polarity and the middle pickup is opposite of the bridge and neck pickups in both wind direction and polarity. An important , but often ignored point about RW/RP is that this was not done on any Fender guitars before 1977, Stratocasters didn't even have a five way switch until 1977, the two and four positions on a Stratocaster were originally a result of "Jamming" the switch between the positions to create a unique sound and all three pickups were "Standard wound", all wound identically in reference to wind direction and polarity. Additionally, the output sound/tone is noticeably different, whereas the "Original" or "Vintage" configuration creates the trademark "Quack" in the second and fourth position, which is a very sought after sound, however frequently overlooked or ignored in terms of pickup buying choices by many.
Wax potting guitar pickups serves two important functions, first from a practical stance, the wax impregnating of the copper wire coil serves to solidify the coil to protect the fine, delicate wire from damage or breaking. Secondly the wax acts to dampen and reduce coil vibration that can occur as a result of the coils being wound too loosely. The loose coils give the pickup a "Microphonic" quality. Most people find a little Microphonic to be desirable, but just a little. The wax is an 80/20 mixture of paraffin and beeswax, the mixture is a result of trial and error resulting in the best of both worlds. Paraffin by itself is too brittle and the beeswax has too low of a melting temperature, together they make a perfect supple seal, this is on of the very few things that can be called an industry standard. Wax potting can be either full potting, where the pickup is actually "soaked" for approximately 10-15 minutes until no air bubbles are present, partial potting is a much quicker submersion, sometimes referred to as flash potting, and of course no potting at all. I suggest full potting, I full pot my own pickups. Pickups that are not potted come with No Warranty.