Keys are an important part of the typing experience. It is after all where the "rubber meets the road". Sadly, many modern keyboard manufacturers have cut pennies on keys so this Wiki entry will help you distinguish the different types of key lettering, give you an idea of how they will wear, and includes some pointers on how to maintain the keys.

Terminology used here is generally the same as on this Signature Keycaps 101 link. For brevity sake "Keys" is generally used here. Keycaps is also used widely but sometimes gets confused with the tops of two piece keys.

Applying key labels can be done in a number of ways:

Two-shot injection molding is one of the best variants and used to be common with high-quality keyboards. Here the keycap (keytop) has cavities which are filled with differently-colored plastic of the same type during production. This allows for contrast-rich labeling, even wear and high wear resistance in general.

Another method is dye sublimation which appears to be used on two-piece IBM keycaps (as well as old Cherry S... keycaps). As noone has complained about wear on these so far, this seems to give good durability as well, or at least may do so provided the base material does. Apparently a certain degree of heat resistance is required, favoring the use of keycap materials which are less susceptible to wear as well.

Laser engraving became popular in the mid-1990s. This also tends to have good wear resistance, but contrast isn't very high.

Pad printed (tampo-printed or silkscreened) lettering may also give good contrast, but tends to be subject to wear.

Some manufacturers have tackled the problem of wear by using a rather ordinary labeling method but coating the result with some more durable transparent plastic - examples would be the "decals" found on Chicony and inexpensive Logitech boards (just the lettering itself covered) or the entirely coated Filco keys.



Here are a couple of websites that will give you a good intro to the various ways to letter the keys.
Signature Plastics
A chinese blog entry
Dye Sublimation in Detail - KeyTech (probably IBMs subcontractor)

Here is a picture of a sample of keys sorted by method. P is "pad printing" or I like to think of P=paint. L is "lasered". S is "dye sublimation". D is "double shot molded" (two-shot molded).

Top left is a Logitech with top and front pad printing next to a Filco key. Second row is a Dell AT101W. Next row are two different IBM Model M keys and a Black on Black Topre key. Bottom row are dual shot NeXT keys. You can see how the D key has the texture completely worn off whereas the power key is almost new.

Pad printed or "painted" keys are what you will find on 99% of all keyboards. Cheap and versatile you can print multiple colors on any face of the key. This is the ubiquitous Logitech/Microsoft "decal" look. You can generally feel the lettering with your fingers since it is sitting on top of the surface of the key.


Here is a Filco key. This is much more subtle but if you look closely you can see the "embossed" look characteristic of pad printed keys. Filco attempts to reduce key wear by a uniform spray over the entire key which is a compromise between looks and wear.

Lasered keys have a etched feel because they are etched! You should be able to feel the scratchiness easily. This is from a Dell AT101W.


You'll often see Cherry Corp keyboards like this as well, since it has been their standard labeling technique for a while. Ivory keys are simply lasered. For how black and backlit keys are lasered see the "Lasered Keys Wiki - Das Versus Filco Fight!".
2002 Cherry G80-3000LPMDE:

Dye sublimated has a "inky" look. You should not feel any surface lettering. It has the advantage of durability and can be printed on any part of the key in multiple colors.


The dye goes down a few microns so the key will get shiny but no change in lettering. This is a cross-section of a cut key.


Notice the difference in IBM keys over the years. From left to right a 1988 Model M APL key, a 1993 mini, a 1993 1391401, a 1991 mini and a 2009 Unicomp grey key. Although durable it is more expensive and today only Topre, Cherry Corp and Unicomp currently ship keyboards with this lettering method.


Here's the Esc key of a 1992 vintage Cherry G81-3079SAD:

As an example for a two-shot molded key, here's one from a 1996 Cherry G80-3000HEMDE:


Double shot keys are easier to tell on shiny keys. You can generally see and perhaps feel the outline where the two plastics meet.


Other clue is the super high contrast you achieve.


The only way to confirm though is to turn over and look for two colors of plastic. This is the volume key above with the green Mute. The Mute is surface printed since the process is limited to two colors.


From the viewpoint of key wear and readability the double shot keys appear to be the clear winner. Unfortunately the process is more expensive and only Cherry Corp. continues to ship new boards with them.

Extreme microscope closeups of the keys and different lettering techniques are in the discussion pages in this wiki entry. 60X and 200X.

Keys frequently consist of a single piece, but there are a few exceptions with two pieces, among them many of the IBM Model M keyboards. Exchangeable keytops (or keycaps) allow for higher flexibility in terms of layouts, as well as custom key labels if transparent. Obviously this is more expensive than one-piece keys, and not quite so obviously it has to be ensured that the keys don't rattle as that may degrade key feel.

Terminology when talking about the various parts tends to vary - one piece keys are commonly referred to as "keys" or "keycaps", but with two-part ones it gets more tricky, with the top part with the labeling being referred to as "keycaps" or "keytops" and the base as "key stem". The part of the switch where the caps slide on is usually also called a "stem" or in the case of ALPS a "slider". The part of the key that attaches to the stem is the "mount".

On the left are single piece IBM keys from a Model M and a M4. On the right is a double piece IBM key.



Key stems come in as many flavors as switches. Top left is a Red ESC Filco key for Cherry keyswitches. Top right is a NeXT key for ALPS keyswitches. Bottom left a Logitech rubber dome. Bottom right is a Red ESC Topre key.


You can generally swap keys from one keyboard to another if the key stem is the same. However, often the larger keys (especially the bottom row keys) may be of different size or have a different stabilization system.

Luckily most keys are sized the same on mechanical keyboard. About .5" wide tapering down to a little less than .75". However the Cherry Corp keyboards are almost 2mm shorter than a IBM, Topre, Filco, or Das. Key Centers are .75" apart row to row and column to column. The keys are staggered in a generally standardized way as well:


The staggering is a purely historical artifact resulting from the design of mechanical typewriters. If you have a keyboard that feels a bit "off", especially the mini layout keyboards, you can measure it with a ruler. This is standard spacing for IBM, Filco, Topre and most standard keyboards. Logitech for some reason often deviates from this.

Measuring the main key cluster from top left edge of keycap to right edge of keycap:
Width 11.00" (CTL to CTL)
Height 3.55" (~ to CTL)

Most keyboards have an indentation on the F and J keys to make it easier to center your fingers on the home row, generally called "nubs". This shows one IBM Model M with one (an APL keycap) and one without.


Many Cherry Corp keyboards do not have nubs but instead "scoop" the F and J keys more to make them identifiable.


Or you can add your own. Nubile Nubian Nubblie Nubs at Hooleon.


Most modern keys use different geometries for the different rows. This is a Topre chart showing different rows. Signature Plastic has a handy chart showing family profiles here (most mechanical keyboards seem to follow the DCS profile)

This chart also shows the key codes for the different rows. Filco keys are labeled R1, R2, R3 for the Alphabet rows, but not the others.


The top of the key can be spherical - normally found on older keyboards.


Or cylindrical - almost all modern keyboards follow this


Or flat - generally found on Point of Sale (POS) keyboards and some numpads.


Or in what is known as a "Chiclet" style as used on notebooks and some scissor switch keyboards


Or even a cylindrical shape but oriented differently.

A HP Mini notebook keyboard


Cherry Keys are slightly lower profile than other manufacturers keys.


Filco

There is a bewildering array of plastics available and when you add in the different additives for softening, the ability to mix plastics, and fire retardants it's not easy to generalize how keys will wear. In addition, keyboard manufacturers generally will not advertise what materials they use in keys and focus instead on cost cutting. These are some of the plastics you may find to be in use:

PS, PC and PVC (Polystyrene, Polycarbonate, Polyvinyl Chloride). Common and cheap. This is a lighter less durable plastic that tends to be vulnerable to solvents. Most keyboards shipping today including Logitech, Microsoft, etc. use some variant of this for their casings and keys.

ABS (Acrylonitrile Butadiene Styrene). It's commonly used for older keyboard casings. It's a comparatively soft material compared to some modern plastics but is resistant to breakage. Topre casings are made of ABS and probably most IBM Model M's are as well. Although I am not sure I suspect Filco and Das keys are made of ABS.

PBT (Polybutylene Terephtalate). PBT is a common choice for modern Cherry keycaps and is what IBM and Unicomp use. It should not yellow as much as ABS over time.

POM (Polyoxymethyleneor better known by the brand name "Delrin"). An abrasion-resistant and low-friction material, this found use in older black Cherry G80 keycaps. However it is expensive and not common in other keyboards.

If you are not sure what plastic the keys are you can do a solvent test with acetone. Just brush the bottom of the keycaps and see if the surface starts to melt.

Das S Lasered Keys - Note that they appear to use the cheaper plastic



Of practical interest is how the different keys wear. Here is a well used Logitech keyboard. You can see the WASD keys are shiny from some serious gaming but the labelling intact.


Often surface lettering (pad printed) will yellow and eventually wear off. Some people seem especially susceptible to key wear because of sweat or some people even claim body chemistry. Here's a pic after a acetone bath. This is an extreme example but you have to be careful with solvents around keyboards. Notice how the label does a good job in protecting against corrosive sweat and wear.


More typical is the "shiny spacebar". This will occur more quickly on matte keys like the Filco/Das and less on the more sandpapery IBMs and Topres. However plastic is plastic and some wear is inevitable. This is a four year old Filco that Majestouch owns.

This is a closeup of a shiny spacebar on a 5 month old Filco that I own.


Here are some interesting posts on key wear:
Das S Lasered Keys Versus Filco Pad Printed Keys - FIGHT!
My opinion on order of importance of the various wear factors. Includes LOTS of pictures from keyboards I own.
Different plastics and Key wear
Das Vs Filco including pics See the discussion portion for lots of pics of key wear
Filco Matte Finish wear
Why Have A Coating?

Large keys, notably the space bar and Ins on the num block, tend to have extra supports to keep them straight in order to avoid key misses when hit off-center. Typically this is a hinged thin metal rod (or thick wire) bent into a wide U or U-with-inwards-facing-sections-added shape. The ends then attach to the ends of the keycap, while the long section rests on the PCB/membrane underneath.
As the keys move up and down, the stabilizer rotates around the long section, being able to slide on either the key or the underground. If one end of the key were to go down further than the other, the stabilizer would get twisted, which it tries to resist. In practice this means that the other end will just fall down to the same height, thereby making the key level again.

Cherry MX Stabilizer on Filco/Das/others


Cherry MX Stabilizer on Cherry Corp/Steelseries/others


IBM Model M Stabilizer Inserts (matching pin in key)


Related discussion:
Detailed Cherry Key Removal Instructions With Pics
Majestouch's Tips to Remove Cherry Keys
PC-compatible keyboard with old-style keys
Removing and Repairing a Scissor Switch Key

Here are a few discussions involving cleaning tips:

Good Overall Model M cleaning guide
Dishwasher Tips
Using denture cleaning tabs (promising method, to be investigated further)
Alcohol?
Dishwasher? (& other options)
SGI AT-101 keycaps dishwasher safe?
Best way to clean a keyboard?
Bulk key cleaning
Disease Prevention - REQUIRED READING

Greasing the key
Topre "Sticky" Sound
Various lubricants
The Mystical RO-59 Lubricant

The difficulty of removing keycaps varies widely. Here are a few tools that may come in handy depending on your keyboard.



On the left are two options for the DIY crowd. More DIY ideas are here. Also, if you have a IC puller handy they work well. In the case of the Model M you can use your hands for most keys (although if you're going to remove all keys it's easier to take out of the case first).

The metal tool (comes with the Topres), the ring, and the wire puller all can work but the wire puller is generally preferred by Geekhackers (available here or Elitekeyboards.com). The white plastic puller works for fast removal of keycaps only.

The ALPS keys are a special case. They are very difficult to remove so I advise using a screwdriver to hold the switch base down while twisting or using a wire puller at the same time. Otherwise this might happen:


Also, be careful on the larger keys with stabilization systems. Be sure to study the section above to learn how they work for your particular keyboard before attempting to remove. IBM spacebars tend to break at this point if yanked quickly or if the keyboard is dropped.


The pictures shouldn't deter you. Swapping keys is not difficult if you take it slow. Plus, it's great fun to customize your keyboard. In addition you sometimes will get a squeaky spacebar or other key. Keyboard manufactures use white lithium grease but Geekhackers have used a variety of lubricants.

Some of the more unusual keys and key trivia are linked here. Feel free to add your "wow-lookie-that-key pic" to the discussion pages.
All About IBM Keys
Bollwerk's Video Editing Cherry Keys
The Mac Command Key or St John's Arms
Hate the Windows Key? - Ubuntu Keys for Cherry Switches
The Battle of The Red ESC Keys
Multimedia keys
IBM Key Discussion and a variety of pics
Bosch Dishwasher Designed For Plastics Legos are made of ABS, sometimes used for keys

Plasti Dip those Shiny Keys!
Sandblast those Shiny Keys!
Rit Dye Mod
Signature Plastics Quotes for 1 to 10 sets of keys
Relegendable keycaps
Cherry Key Swap - Cherry Corp Double Shot keys on Filco
SGI Keys on Filco ALPS keyboard
All Black Unicomp Blank Keys - same steps for IBM Ms
All Blank Filcos - Make any Filco Cherry Keyboard Otaku
Thumb Hurts? - Reverse that spacebar
Hate The Windows Key? - Lots of Alternatives
Thumb Hurts On A Model F? Loosen spring mod
Cherry Key Silencing With Dental Bands