Basically what the title says. It is possible to cast a spell that allows you to coat a real sword in fire? I want a Wizard that has a decent weapons skill. So I was wondering If I would be able to do something like this in game.
What, now you want how to do it? Sheesh.
I assume you already have a sword.
First, you could have made it an enchanted item like Harry's force rings. Actually, I'd copy the force rings whole, change the numbers to fit your Lore, and change it so the spell is targeted with Weapons. Boom, extra damage a couple of times an adventure. Slightly more complex, but something most tables and GMs will be fine with, is taking two or three shifts out of the 'damage' part of the enchantment and having the sword give itself the aspect "On Fire" when you use this. This gives you a single strong attack, and gives you an aspect you can free tag once and can tag normally for the rest of the fight.
Second, you could cast an evocation to make a normal sword have the aspect "On Fire" and then tag that (again, getting a free tag the first time) as you need. That'd probably last you a couple of rounds, though since magical fire behaves like normal fire in the dresdenverse, your metal sword would stop being on fire fairly quickly after you stopped focusing on it. (You could make the sword out of wood, but then it becomes single use.) Evocation is always a block, a move, an attack, or a maneuver; this is clearly a maneuver. Offhand, I'd say two or three shifts of evocation should do it- consult your table/GM as needed. If I were at your table, I'd be sympathetic to more shifts making the spell last longer.
Third, you could always use thaumaturgy. That is the go-to for more complex or long lasting spell effects. This isn't exactly tricky; Again, I'd go with two or three shifts for the base "On Fire" aspect, then more shifts for more time as per normal thaumaturgy rules. Additional shifts might get you additional tags, but since you'll have to get those tags with other aspects to boost your complexity, it's not normally useful. This kind of solves the duration problem (While magical fire is still fire, thaumaturgy lets you be a little more wibbly wobbly with things) but gives you another problem; that of how you're going to carry a flaming sword around. Dresden Files doesn't exactly have a harshly enforced masquerade, but you're supposed to make at least a token effort. Credit to Ballsun-Stanton- you could probably use a fireproof sheath to conceal it. If I was GMing your game, I would compel On Fire to make that go horribly wrong somehow, but then it's not like any good FATE GM lacks ways to make your life interesting. I don't exactly recommend this route, due to the long prep time to get it running. The exception would be as preparation for a big throwdown, as spending a few hours magically buffing yourself before the third act is a time honored Dresden tradition.
Fourth idea! If it's going to be an important part of your character, why not make it an aspect on your character? I'd still think about how this happens so you've got some kind of fluff excuse, and some tables are more strict than others on aspects, but this could totally work. I've had plenty of players with "My Father's Sword" or variations on that theme. In story, it's an enchanted object, or it's a spell you've perfected, but making it an aspect gives you several benefits. First off, this makes it bad form for the GM to deprive you of it for extended periods- or if you are deprived of it, you get those lovely fate points! Second, it means you can always tag "My Flaming Sword" to get a bonus, even in situations where you aren't hacking and slashing. (Intimidate bonus?) I'd generally pair this idea with one of the above, but this also opens up the idea of taking supernatural powers and reskinning them. Venomous looks good- use Weapons instead of Fists, and burning instead of being poisoned, but otherwise looks good. Note: There's a 'power' called Item of Power that models this- you attach supernatural powers to it, pay refresh (with a discount for it being something you only get if you have the weapon) and there you have it!