The Original Rare Attributes
The original rare attributes (Blast, Blind, Disease, Panic) appear to be more common than rares with clan-specific attributes. These special types of rares are unique and can't be chosen as an ability by clans.
Weapons with clan-specific attributes were introduced to the game in the DC Upgrade of May 2005. They are harder to find than the original rare attributes, and certain abilities, such as Merchant and Popular, are highly sought after by traders.
Clan-specific rare weapons are basically the same as the abilities that are granted to clans. Unlike clans, rare abilities on weapons will continue to function even if you haven't logged in for more than 2 weeks or have temporarily lost all clan standing. However, unlike weapons, clan leaders have the power to choose which abilities that they want for all of the members of their clan to have.
None of the rare attributes are stackable; for example, equipping 5 rare weapons with Popular will not make it 5 times easier for you to gain rank and equipping 2 rare weapons with Strong won't increase your overall attack by 20%. Likewise, clan abilities and rare weapons can't be stacked together.
Weapons that come with Bless, Glow, Lucky, or Flames aren't considered to be rare weapons. No matter how unusual it is to find a Leather Jacket with Flames or a War Tusk with Lucky, weapons aren't considered to be rares if they come with attributes that can be assigned to them with scrolls. In addition, weapons that come with rare attributes that are normally associated with the weapon aren't considered to be rares. Here's a list of weapons that will always have a specific rare attribute and aren't rare weapons:
Foul Axe with Disease
Imacaci Mask with Panic
Matchlock Rifle with Blast
Rat Tail Whip with Disease
Spirit Katana with Panic
Silver Elf Bow with Blast
Silver Gladius with Blind
Silver Masamune with Panic
Silver Rat Tail Whip with Disease
Silver Weird Knife with Disease
If you find any of the weapons listed above that doesn't come with the corresponding attribute, this "rareless" weapon actually qualifies as a rare weapon. Although it was once possible to find "rareless" weapons, such as Foul Axes without Disease and Miners Caps without Glow, rareless weapons can no longer be found in the game. Instead, when a weapon is supposed to come without its normal attribute, the attribute is automatically added to the weapon again and replaced with a capital letter. Weapons with a capital letter for Bless, Glow, Lucky, or Flames can't be deemed as rares since this can be achieved by applying its corresponding scroll to the weapon. Weapons with a capital letter for Blast, Blind, Disease, or Panic, however, can be deemed as rares since there are no scrolls that can apply these attributes to weapons.
An exception can also be made for weapons if their "replaced" attribute precedes a rare ability that isn't normally associated with the weapon. As an example, take a look at these two weapons:
Amini Clubs normally come with Lucky, but this particular AC has a capital letter for Lucky because it wasn't supposed to come with Lucky. Normally, this can be achieved by applying a Luck Scroll to an Amini Club, but because this AC's Lucky precedes Blind, a rare ability that isn't normally associated with Amini Clubs, we can tell that a scroll wasn't used to add Lucky to the weapon. Similarly, Great Targes don't naturally come with Bless, but because this Great Targe's Bless attribute precedes Panic, we can be certain that a Bless Scroll wasn't used on the weapon.
Double rares, weapons that have two rare attributes, do exist in the game and are often sought after by those who enjoy collecting rares. Of course, rare weapons that come with "false" rares, such as a Masamune with Disease and Glow, aren't considered to be double rares.
It's always been speculated that a weapon may be able to come with three rare attributes, and apparently, this is possible today. However, double rares are hard enough to find, so you can imagine how hard it'll be to find a weapon that comes with three or more rare attributes.
Oh, curse it all!
Although curse isn't often considered to be a rare attribute, there have been players who have expressed some interest in collecting cursed weapons. Trading a cursed weapon, however, isn't easy - the only way to take off a cursed weapon while retaining the curse is by applying a Glow or Flame scroll to the weapon and then having a Worm, Serpent, or Anaconda eat it. There's a good chance that the creature will run away with the cursed weapon, but if you're lucky, the cursed weapon will be regurgitated back into your inventory:
Before the 2002 DC upgrade, War Boots and Spirit Katanas were by far the two most commonly cursed weapons.
Rares and Gear Position
The most valuable position for rare weapons is likely to be the Head slot. Rare headgear is difficult to come across and the head slot is often the most expendable of the five slots, making it feasible to sacrifice a decent helmet in favor of gaining a rare ability such as Agile. The next most dispensible slots should be in the following order: Feet, Left, Body, and Right. This is basically the order from the least important to most important slots.
"What Happened in April?" (Judge Judy)
After the DC Upgrade on April 8, 2002, rare attributes became effective regardless of the position of the weapon. For example, a Shuriken with Blast could now inflict Blast damage whereas it couldn't do so before the upgrade. Before the upgrade, only rare attributes from Right and Right/Left handed weapons were effective. Rare attributes from weapons of other positions were considered to be novelties.
Rare Abilities in the PastBlast inflicted only 25 damage before the 2002 upgrade.
Medic healed only 20% more guts before the 2003 upgrade.
Popular made it 30% easier for a character to gain rank before the 2003 upgrade.
Upgrades to the game have changed the functions of several abilities:
Rarity of Rares in the Past
Before the DC Upgrade on April 8, 2002, rares were considerably more valuable than they are today because they were a lot harder to find. It wasn't too uncommon for someone to quest every single day for a whole week without coming across a rare. Today, players can expect to find a dozen or more rares in a week.
Great Bows may have been the most common weapon to come with rare attributes back then.