Someone gave me a very nice set of chisels that hasn't been in use since years. The only problem was that it was in pretty bad shape. None of the chisels was sharp and you could clearly see some abuse from hitting nails, opening cans and using coarse grinding wheels (don't do any of these).
As the tools had quite some emotional value for the previous owner I didn't interpret it as a gift but more as commending them to my care. So I put some love into them and started a restoration project.
These were the first chisels I sharpened but as I got a lot of them I got really some practice over time. Not all methods were good and I finally stuck with one that Paul Seller presented on his YouTube channel and for which you don't need any honing guide. It's nice to give new chisels a good initial grind or to save old tools.
Step 1: Sharpening Stones
You need some water or oil stones to get the chisel sharp. Have a coarse one of about 240 grit, a medium one of about 1000 grit and a fine 3000 grit stone. I use Japanese water stones but which ones exactly you use doesn't matter so much. You can also buy combination stones that offer you two different grits in a single stone.
As I repair a lot of badly treated blades by 240 grit stone wore out very soon and I invested in a 400 grit diamond stone instead. These loose there sharpness a bit but last a lot longer than other stones. At which grit you start depends a bit on how bad your blade really is. I needed to use a 180 grit stone for some.
If you already sharpened several tools on a stone you need to level them on a flattening stone again. Otherwise they develop a hollow that then transfers on to your blade. This hinders you from achieving your desired grind angle. Simply scrub your sharpening stones over the flattening stone in a circular motion.
To prepare you water stones let them soak in water for about ten minutes. Oil stoned simply get some nice drops of oil and diamond stoned get sprayed with soap water.
The stone will slip if you just put it on the desk. You can use a wet towel or an anti slip mat but my experience is that a dedicated holder works best.
Step 2: Clear the Back
You start on the coarsest stone with the chisel's back. It can be a good idea to mark it with a sharpy to identify high and low spots after grinding. Put the blade flat across the stone and move it back and forth. Water stones need some additional drops of water when they get dry and make sure not to remove the slurry as this is what actually sharpens the blade.
Wherever you still have marks after the first passes there's a low spot. Make sure that you grind down until the marks on tip and sides are removed. It's okay to have a low spot in the centre but don't leave a high spot there. Otherwise you can't guide the chisel precisely. Continue on 1000 grit and 3000 grit.
This usually has to be done only once in a chisel's lifetime.
Step 3: Get It Sharp
Then turn the chisel such that it is aligned with the sharpening stone and flip it so that the chamfered side points down. It can be helpful to also mark it. Position the blade so that you have about a 25-30° angle to the stone surface. Move it gently forward. The natural motion will lift the tip slightly up so that you will create a bevel over time. That's absolutely fine and I haven't noticed anything negative about working with it. Move the chisel back and try to achieve the initial 25-30°. Repeat this motion until every bit of the blade has been ground. You can see it by the reflection on the metal or by the sharpy marks. If you touch the back of the blade you should feel a burr. Work your way over a 1000 and 3000 grit stone again. Always remove all marks from the previous passes.
Step 4: Polish
You can use a strop to add an extra bit of sharpness. That's basically a piece of leather glued to a board. Rub some polishing paste or abrasive onto it, press the bevelled side of the blade hard down at 25° and pull it back about ten times. When the metal is mirror clear at the tip put the flat side down and give it a single firm pull to remove the burr.
Now enjoy a wonderfully sharp tool.