One of the questions i see fairly often on the various forums is "how do you sharpen a spoon knife?", well the answer is simple and very cheap, there really is no need to go out and buy expensive water stones or slip stones, all you need is a bit of flat wood with radiused edges, a piece of thin leather and some 600 grit wet & dry, total cost?, probably less than a quid.
I first came across this method when i was watching one of Ben Orford's video's on You Tube and to be honest, it's such a simple no fuss method of sharpening a hook, crook or spoon knife it's a wonder more people don't use it, i have built my own system up with the addition of more 'sticks', but it is based entirely on Ben's method.
I have two sets of strops made up that i rotate as i use them, the picture shows my sets, by the way, i consider a "set" to be one stick with abrasive on and one stick with leather on, the picture, the top stick has well worn 600 grit paper on it and it's probably more like 1500 grit now, it's that smooth, the next stick down has brand new 600 grit on it, the third one down has a fresh coat of pig leather and finally the bottom stick has a well used piece of pig leather on it.
I know my spoon/hook/crook knives need sharpening or at least stropping mainly through experience, but a good indication is when you have to start applying pressure to the cut and or you start to see lines or marks in the wood when the blade has passed through it, meaning your blade is dulling and/or has a minute nick in it, if the blade is just dull i will just use the leather strop to bring the edge back, if it has a nick i will go to the W&D stick to remove the nick, as with all knives, only sharpen when you have to as each time you do it, you are removing metal, if i feel i have to use the W&D stick i will start on the newest 600 grit, then go to the worn piece, then i go to the leather strops, using the brown one first then the grey one, this i find brings up the edge to beyond shaving sharp if you do it right.
It's probably best to watch Ben's video's on the methodology behind the system than me trying to explain it.
There you have it, what i think is the most effective method of sharpening a spoon/crook/hook knife there is, give it a try, you will be amazed at just how simple and effective it is.