Some time ago, I was sought out by client to discuss the subject of blessing a knife to make it safe & ready for ritual. I've been meaning to write about it here for quite some time now, so I hope this information is useful to you.
Knives are, without a doubt, a much maligned tool, and they are illegal in some areas. In others, you have to pick the right tool for your locale. It does and doesn't matter what you pick, here. I'm not going into that today, as there's too much to talk about in that arena.
Once you've selected your chosen tool, its time to imbue it with energies and intentions that work for you. There are many manners of doing so, and thus I provide you with one.
Procure water from a local stream, rainfall (assuming its not illegal to collect rainwater in your area), or a river. If you don't have access, use tap water instead. Mix one cup of water with a teaspoon of kosher salt. Over that salt, say the following: "I bless you according to the merits of your ingredients & the rightful benedictions of your Creator."
As you do this, think about the process of this mixture being infused with essence and import, of significance and heart. Feel it come alive in your hands.
When this life has been imbued and the associated state achieved, place the blade of your chosen tool in the concoction and say "Tubal-Cain, lord of the Forge, I ask your blessing of this, my tool that is cousin to what you've made in your Shop. Let this steel come alive in my hands and be made useful to me."
Afterwards, light some incense that you believe would be appropriate. You're free to choose what works for you.
Then on, each time you sharpen your knife, be sure to offer the iron filings up. They might not seem like much, but that's incredibly important to a spirit of craftsmen: its a sign of use of the craft they chose to master.