I have a small craft knife (almost like a scalpel, really) that's become rather blunt over the years. It's no longer safe to use because it's so blunt, so I need to sharpen it.
What are the safest ways to do this, considering its small size?
If the knife is really that blunt, I recommend taking it to be professionally sharpened. Many craft stores offer this service either as part of their regular services or on a part-time basis (once or twice a month). Otherwise, you may have a knife sharpener in your city who would be able to do it. The cost is generally based on the length of the blade, so should not be very high for your knife.
Unless you have a good-quality mechanical sharpener at home and know how to use it well - or have learned how to use a whetstone and steel, it will be difficult for you to return the knife to the necessary level of sharpness for crafting.
Honers can only realign the blade slightly and are for daily knife maintenance, they can not actually sharpen a knife.
With a so small blade the best is to use a grinding stone. If it is very blunt you will have to start with a coarse grain and finish with a fine one. It will take a long time...
Blades generally have a 15° angle on each side.
V shapeners are quicker but use it with care. Some cuts a lot of steel at once if you push too much. Also it maybe not the easiest to use with a tiny blade.
Note that craft knifes of this size are generally reckoned to be disposable, and new are really sharp, but don't hold their edge well. I prefer a proper scalpel (or second best an X-Acto type) where only the blade is replaced but I've had a few where a scalpel blade was permanently moulded into a plastic handle, and it does seem rather wasteful to go chucking them out.
This would be a good opportunity to practice with a stone, which is quite easy on a straight blade. There are a few options, but I'd choose a double-sided (coarse/fine) oilstone, just a cheap one to start with.
The hardest part is getting the tip really really sharp, which is an issue if you're using the tip to cut out stencils (just as an example) but completely unimportant for sharpening pencils (extreme example in the other direction).
