Whip making is a craft which does not lend itself to mass-production; each piece of leather has individual characteristics and must combine with the others to deliver a unique, harmonious whole. Hence, the first piece which goes into the core is as important as the overlay and is worked accordingly.
Of all the leathers on this planet, kangaroo receives universal acclaim as the finest plaiting material. Properly prepared, it is several times stronger than cowhide and the density of its structure gives clean edges to the strands, which may be cut much narrower while still retaining the strength of the leather. I only use the best leather I can get my hands on, specifically "whip tanned" - bark tanned, bark dyed and drum stuffed (tumbled in a drum with grease and heat) - then further prepare it myself. Colours range from natural tan through to very dark brown, bordering on black but with more depth.
Another heartening thing about this leather is the minimal environmental impact of its manufacture. Unlike most cowhide and indeed a lot of roo, no chromium salts or harmful dyes are used in its preparation. Furthermore, the brush clearance which used to go on to obtain grazing for cattle also favoured kangaroos. There are now more roos in Australia than ever before, so much so that they are frequently considered a pest. The Aussies are not dim, however, and manage their resource. Roo hunting and the export of roo products is only legal with a permit. Every shipment of skins I receive is accompanied by a certificate showing compliance with the regulations.
Take a whip made entirely out of one piece of hide - a traditional southern African sjambok, for example, which is whittled down from a length of thick rawhide (hippo, buffalo... whatever is available, I suppose. These days they are hand done from old poly bags or mass produced from PVC). Such a whip, when bent, will have a lot of compression force on one side and tension on the other. This makes it quite stiff and prone to failure. If you have a smaller core and wrap two sets of interwoven strands down its length - ie. plait over it - until it is the right thickness, the strands can move a bit and so spread the forces around. As the whip is pulled by the wave of energy passing down it the strands tighten around the core like a Chinese finger trap. This lowers the hysteresis and gives good energy transfer.
The "plaited belly" method of construction refines this principle. Here the whip is built up in layers. Around a small core is a plaited layer which may, depending on the weight and type of whip, then be encircled by a bolster of thin leather. Over and beyond this is plaited the overlay or, depending on the whip, another belly (with or without bolster) and then the overlay, which is the top layer. Since plaiting adds two layers of leather, a decent sized bullwhip could have up to eight layers of leather tightly encircling the core. The result is good handling, efficiency and longevity.
I have a couple of six footers (plus fall and cracker - 9ft). One has an 8-strand plaited belly, a bolster and a 20-strand overlay, with all plaiting done in thick kangaroo. The other, in thinner roo, has a smaller core with an 8-strand belly, a 12-strand belly and a 20-strand overlay. No bolsters. They both handle beautifully but the first is noticeably heavier and slower while the other is like lightning.
In general and up to a practical point fine plaiting is better than coarse, eg. 16 strands compared to 8. The stresses in a fine plait whip are more evenly spread and the ability to plait narrow strands tighter makes for more efficiency as less energy is lost in damping and friction. However, if the whip is intended for rough use - stunts, for example - wider strands in a coarser plaited overlay will resist impact better and the thicker leather most suited to this is best cut a bit wider anyway. 12 or 16 strands would be a good compromise for a rugged bullwhip while 20, maybe 24, will optimise fine handling.
The end of a cracking whip (classic bullwhip or stockwhip for example) is going to take a lot of stress yet must be quite narrow. In order to minimise damage and facilitate maintenance the last two to three feet consist of a replaceable section - the fall and cracker - which is generally not quoted in the whip's length.
The fall is typically a tapered strand of particularly strong and suitable cowhide or alternatively another plaited section of 4 strands. It can be expected to last well enough if not bashed about too heavily. Replacement of a traditional fall takes a bit of skill but could be regarded as maintenance rather than repair.
To the end of the fall is attached the cracker. This is the business end which makes the noise and varies from a bit of string to a finely balanced component, well designed for its role in life. Twisted twine gives a good, rounded sound while alum tanned deerskin (hand prepared by a mate to a 16th century Venetian recipe) has a wetter, more slicing sound. It is also soft and lacks the abrasion of a twine cracker - good for neck wraps and other techniques involving a partner - yet is the best I've come across so far for target cutting with the tip. For cutting more robust targets with the length of the cracker twisted or plaited Dyneema seems to be the thing.
When one strikes out with a tapered thong whip (bullwhip, stockwhip, etc.) a wave of energy is sent down the thong. Energy is largely conserved, minus losses due to friction and damping, and since kinetic energy equals half mass times the square of the velocity it follows that as the sectional mass of the thong decreases due to its taper, the velocity will increase. When a whip cracks it is because the difference in sectional mass between the butt and the tip accelerates the latter beyond the speed of sound, producing a sonic boom. A decent whip can generate speeds in excess of 1400 feet per second. That is in the same league as a .357 magnum.
Aside from the balance and harmony of a whip, which are aspects of quality, much of a whip's handling is dictated by the rate at which weight is swapped for speed. A whip which retains more of its weight further down the thong will be quite slow in the first part of the stroke but will pick up speed later. The advantage of this is that less energy is lost in air resistance (which is proportional to the square of the velocity at any point) and a slower whip is also easier to see in action making it useful for some stunt/show applications.
A whip with a faster action will have a more pronounced taper near the handle and will take less time to lay out, making it more suitable for fast multiple cracking and targets, particularly if they are moving.
As to the mass of a thong for any given length, that is a matter of preference and intended use. A light whip might be suitable for indoor performance work, particularly for the slightly built, but for practical use in windy conditions a heavier thong would be preferable.
Most whip thongs are made entirely out of leather so will have a fairly uniform density. In order to increase the difference in mass between the butt and the point without adding to the diameter of the thong and radius of the coil (making it too stiff), lead weighting or shot loading may be employed. The result is a harder hitting whip or one of equal efficacy but reduced thickness. The downside is that the step in density between the weighted and naturally falling sections, however slight, will cause a small upset to the handling. Moreover, the weighting has little or no inherent strength or firmness so causes stresses in the whip reducing its lifespan and efficiency. Most bullwhips and stock whips are naturally falling while short, narrow whips like signal whips have lead in their core.
A well made whip with a tight braid will be rather stiff when new and will need to be gradually broken in. Simply use the whip and it will steadily improve for a couple of years. Running it through your fingers and generally playing with it will also help but do avoid forcing it unduly or oiling the thong to soften it - these practices prevent the whip from bedding in as it should.
The thing which kills whips off is accidents, mainly unwanted impact, usually with something hard, sharp or rough. Take care to hit only what you intend to - and that is your responsibility - paying due attention to back swing and follow through. Try to keep the whip off the ground as abrasion is also an enemy and your beloved whip will stay shiny for longer.
As to routine maintenance, I generally give my whips a light going over with saddle soap after they have been out. There are lots of preparations on the market which are good for whips. Every few months I use the elegantly named Sedgwick's Original Leathercare Product; a couple of friends use Pecard's.... do refrain from dousing it with neatsfoot oil, which should only be used sparingly on old, dry whips to revitalise them.
Whips seem to do well on air and light, without direct sun. Tapered thong whips should be coiled fairly loosely following their bias or, if short, hung up. Riding crops, if stood on their tip, will develop a bit of a cast so standing them on the butt or hanging them up is preferable. If a whip is to be stored for any length of time, it is still a good idea to give it a once-over with saddle soap every now and then. A lot of plaited whips, if left unloved for too long, will develop a white bloom at the edges of the strands - residue of the various substances used in the manufacture - which can be wiped off with a bit of paraffin and is not a problem. Just their tacit plea for exercise.
This is a distillation of some 35 years mucking about with whips, the last 14 professionally. Some of the above is a result of my own findings, some is my take on received wisdom. If any of it is factually incorrect or if further elucidation is required, please do not hesitate to get in touch.