The basic building block for any colored, this can be made by crafting 1 stick and 1 rock together. This can then be mixed with any soul to obtain any of 4 traits (Damage, Slowness, Knock back, Speed). Mixing it with a Bottle C, or Bottle A will allow you to acquire all 4 traits on the same sword.
 Blue, Yellow, Red, and Green Daggers.
Each of these daggers can be crafted by mixing a dagger with any soul found in the cave. Souls can be collected by using a bottle.
The blue dagger increases attack speed
The yellow dagger increases knockback
The red dagger increases damage.
The green dagger slows enemies.
A C dagger does all of the traits listed above. It can be crafted by mixing a Bottle C (Dropped from Yellow Boss) With a dagger (see above)
The best dagger in the game as of now, mix two bottle C's together to get a white bottle, put it on your dagger to make Dagger A.