Here are a few more gleanings on Spanish knife culture from 19th-century travel writers.
Théophile Gautier wrote the following in Travels in Spain (1901):
At Santa Cruz we were asked to purchase all sorts of pocket knives -- navajas. Santa Cruz and Albacete are famous for fancy cutlery. The navajas, made in the most characteristic Arabic and barbaric taste, have open-worked handles through which show red, green, or blue spangles. Coarse inlaid work, but designed with dash, adorns the blade, which is fish- shaped and always very sharp. Most of them have mottoes, such as Soy de uno solo (I am one man's), or Cuando esta vivora pica, no hay remedio en la botica (When this adder stings, there is no antidote in the pharmacy). Sometimes the blade is rayed with three parallel lines inlaid in red, which gives it a most formidable appearance. The size of the navaja varies from three inches to three feet in length. Some majos (peasants of the better class) carry some which, when opened, are as long as a sabre. A spring or a ring to which a turn is given secures the blade in a straight line. The navaja is the favourite weapon of the Spaniards, especially of the country people. They use it with incredible dexterity, wrapping their cloak around their arm by way of buckler. The science of the navaja has its professors like fencing, and navaja-teachers are as numerous in Andalusia as fencing-masters in Paris. Each navaja expert has his secret lunges and his own particular strokes. It is said that adepts can tell by looking at a wound to what artist it is due, just as we can tell a painter by the touch of his brush.I'm intrigued by the claim that "adepts can tell by looking at a wound to what artist it is due," implying that every knife-wielder inflicts enough wounds on different victims that a recognizable pattern is established. That reminds me of the scene in The Good, the Bad, and the Ugly in which Clint Eastwood recognizes his opponent from the sound of distant gunfire, observing, "Every gun makes its own tune."
From Henry George O'Shea's O'Shea's Guide to Spain and Portugal (1889), there is this:
La navaja, or cuchillo, often as long as a common sword, settles at once all differences of opinion, blood being thought to wipe off any petty rancour. It is used very frequently, and has become an art in which the barateros are proficient. A baratero ( from barato, cheap) lives by his knife. He frequents gambling circles, and receives some coins from the cowed-down players whom he has threatened to disturb if they should not grant his boon. This is called cobrar el barato, "to get change." In some cases, one of the challenged parties gets up and refuses to pay; upon which the champion fights. Death often ensues, as the stomach is aimed at. Those curious to learn more particulars may consult 'Manual del Baratero,' with prints. The best specimens of knives can be had at Madrid and Seville; they are principally manufactured at Albacete; they have bright colours on the blade, with mottoes; a muelle or catch; the price varies from 6r. to 30r.From Samuel Parsons Scott's Through Spain: a Narrative of Travel and Adventure in the Peninsula (1886):
The baratero is a character not peculiar to Malaga, but who attains his highest development in that city. The word means, in plain language, a blackmailer of gamblers. This ruffian rarely plays himself, but never fails to be on hand when a game is in progress. After the winner has gathered in the stakes, he pays over a certain proportion—usually five per cent—of the profits to the baratero. If any hesitation is manifested to submit to this extortion, a fight is inevitable, and, as the baratero is always an adept in the use of the knife, he is morally certain to get the better of his opponent, who loses at the same time his money and his life. No amount is too trifling for the consideration of this ravenous bird of prey, who pockets a few cuartos with the haughty insolence with which he demands a doubloon. The quarters of the city frequented by gamblers are divided into districts by the barateros, each of whom, inspired by that traditional sentiment of honor common to criminals, is careful not to encroach upon the province of any of his brethren; the danger of such interference, moreover, being aptly expressed by the saying, "Nadie se meta a Baratero sin contar antes con los Eserilanos." ("Settle with the magistrates before picking a quarrel with a baratero.")
The skill displayed by the Spanish desperado in handling his knife is wonderful. This weapon, to which all are so partial, is a wicked-looking affair, from one to two feet long, and called a navaja from its resemblance to a razor. The blade is of the finest Toledo steel, and bears the motto common to the side-arms forged upon the famous Tagus: "No me saques sin razon; No me envainen sin honor." ("Do not draw me without cause; Do not sheathe me without honor.")
Defence with the navaja has been reduced to a science, which has its regular school of instruction. The teachers give lessons with wooden knives, and the most noted among them have their private strokes, which are kept secret for cases of emergency. The arts of the most accomplished swordsman are worthless, when opposed to those of an expert with the navaja. With his cloak or jacket wrapped about his left arm, his formidable weapon glittering in his right hand, and his lithe body poised for a spring, he is an interesting study for the spectator, as well as for his antagonist. The thumb is pressed tightly along the back of the blade, that every advantage may be taken of the flexibility of the wrist, in a struggle where the space of an inch is often a matter of life and death. The postures and guards are changed with bewildering rapidity, and, should the right hand be disabled, the cloak and knife are shifted in the twinkling of an eye, and the duel proceeds, until one or both the combatants are killed.
Hand-to-hand encounters are most esteemed by professors of the navaja, but there is a class of them who make a specialty of lodging the weapon from a distance in the vitals of an enemy. They become perfect by throwing it at a peseta fastened to a piece of cork, the coin becoming the prize of the winner. When one grows skilful enough to hit the mark twice in three times, at ten paces, he is ruled out of the contest, and is recognized as a diestro. The blades of these knives are contrived with devilish ingenuity so as to inflict painful and incurable wounds, and are grooved, like Indian arrows, to permit the blood to run freely. All the thrusts and parries used by experts have their technical names—the navaja itself being termed an abanico (" fan")— which are as unintelligible to the non-professional as those belonging to the comprehensive jargon of the bull-fighter.