Acid etching can bring out the hamon on blades that otherwise might not show one at all. For more information on what it is, click here.
If you decide to proceed with this, you should know that although this usually goes to plan and the internet is flooded with success stories, you do so at your own risk. You should never do this with an expensive blade. ever.
In order to etch your blade, youre going to need a few things
- Can you fully dissasemble your sword? You will need to do this to stop acid getting underneath the habaki and into the tsuka. You will want to be using just the bare blade.
- Your etchant of choice in a suitable container. I'd love to be able to say which one to use, but I feel it's probably best that you ask around and/or experiment yourself. Lemon juice or vinegar are in my opinion the best simply because they aren't as caustic as ferric chloride and they are more easily available.
- Rubber gloves. Not so important with lemon juice or vinegar but as important as hell with ferric!!! no kidding.
- Cup of Bicarbonate of soda / water
- Kettle full of freshly boiled, hot water.
- A few cloths.
- A metal polish such as mother mag or if youre in the uk, something like 'peek' will do but you have to be real careful about how much you use as it has a habit of just removing any and all of the etch if youre not careful.
I'm going to assume that you know how to disassemble your sword and that you have done so, leaving you with just the blade. Now, you will need to make sure that it is clean. I use washing up liquid and a soft cloth as it removes any grease or oil that may be on the blade. Make sure that its rinsed and dried off afterwards.
If you want to wear gloves, you may now put them on ;)
Next you will need to use the hot water to heat the blade. Etching seems to take best when the blade is warm. If youre using vinegar or lemon juice, you can also preheat this for the next step, but be careful as the fumes can be pretty unbearable.
Taking a cloth and your chosen etchant and watching those all important fingers, wipe it up and down the blade on both sides making sure that the whole thing is covered evenly. keep doing this, dipping the cloth in the liquid and wiping up and down the blade.
As you do this, the colour of the steel will darken. It's at this point when you stop wiping the etchant with the one cloth and use the bicarbonate and a different cloth to neutralise the acid. Dont be shy with the amount you use as you want to stop the acid working any further.
Looking at the blade, you should see that it has darkened and you may well see the hamon now fairly visibly. There will also probably be areas of the blade that have discoloured more than others. Don't panic, this is perfectly normal. Using the mothers mag and another clean cloth, carefully polish out these 'blotches' and imperfections. Dont worry about lightening the colour too much either as you can continue etching the blade until you have the effect you want. Just concentrate on making sure that the colour of the blade is consistent all the way along.
Repeat this etchant -> bicarb -> polish cycle until you're happy with the way the blade looks.
Once you are sure you are happy, the colour is consistent and and you have the hamon showing as you want it, you can finish it off by polishing the shinogi-ji and the mune back to a more shiny finish.