The Athame is a black handled, straight, two-edged knife that represents the element of air and / or fire and is used commanding of spirits, and, most aptly, making symbolic divisions, the most common of which is the casting of a circle, a cutting out of sacred inner-space in which to work.
As the Atheme is not generally used to cut physical materials, the decision of whether or not the blade should be sharpened is up to the user.
Katana as ritual sword
A friend of mine posted this info on using a Katana as a ritual sword. Reprinted here with permission.
Since the katana has been mentioned of late I thought I'd mention how it is usually used as a ritual sword as opposed to the usual double edged European sword. With the katana any projecting energy is done thru the blade edge,receiving energy is done thru the back side of the sword. The same applies to the 2nd sword,the smaller wakizashi as well as the 3rd blade the long knife known as the tanto. Since many of the Japanese swords sold today are mostly decorative and the handle being plastic some have argued that spiritual energy won't move along the handle properly but that is often a matter of the user's personal beliefs about plastic,most of which is oil based and that means it contains carbon which will conduct spiritual energy,but even if you still have issues about plastic handles,your energy can jump from your hand to the steel of the blade within the handle and thru to the tip or from the tip back to your hand,depending on if you're projecting or recieving energy.