File Knife Seax pt.2 Etching! With acid!

The reason I was making the file knife in the first place was to try out some etching. We don’t do etching at the forge but its something that I wanted to learn so I just went for it.

In between this and the last post I hardened the blade by heating it to a bright yellow and then dipping the edge into oil. Bright yellow is pretty hot and was a risk as I could have easily cracked the blade, but as I don’t know what the steel is I wanted to be sure that I had taken it past its critical temperature. If I had failed to do this it would have remained as soft as it was before heating, or have gotten even softer. By dipping the edge into the oil rather than plunging the whole blade, I reduced the shock as only the edge would suddenly contract. This gave me a hard edge with a softer spine to balance it out, and also meant that I might get some cool patterning at the edge called a hamon (more on that later).

To do the etching, I decided to use ferric chloride in an aqueous solution. Its quite easy to get from electronics stores as it is used to etch circuit boards. The first time I tried it, I only masked off the pattern I wanted and left the rest of the blade bare. This was a big mistake as by the time I had started to see the pattern distinguish itself the rest of the blade was deeply and horribly pitted. Oh dear, back to the grinder to remove the worst of the damage, then try again:

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This time I blocked off the entirety of the blade to protect it from the etchant and sliced out the pattern with a sharp knife. The resist (purple bit) is cheap nail varnish and the black is where I used a permanent marker to tidy up the edges as the marker stops ferric chloride from eating the steel. The hearts are a classic pattern, although not on seaxes, and the text is a snappy bit of an occult phrase.

I plunged the blade into the etchant and left it for a couple of hours as ferric chloride is pretty mild to steel. I got a light etch, but I wanted something bolder, so I bought sulphuric acid from the hardware shop. That sounds hardcore, but its actually a fairly extreme drain unblocker! I diluted it and stuck the blade into the new solution. The steel immediately started to bubble and after about a minute the resist started to fall off. I quickly pulled it out and neutralised the acid with bicarbonate of soda. Once again, the blade had some random pitting and the edges of the design were a little ragged, but I think that a double coat of resist might sort that out on the next blade or i might make a wax/tar mix which is much more hardcore. Here it is with the resist removed and a bit of a polish:

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Its a nice etch, about 3/4mm deep and with a rough base in the deepest areas. I’m pretty happy with it as a first go, although the next one should be a lot better.

After I had it clean, I decided to throw caution to the wind and break out the ferric chloride for a further surface etch. I outlined my original etched pattern to give it a bit of protection as I was a little worried that I would undo what I had already achieved. Here it is as I started outlining:

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As I had only quenched the edge during the heat treatment, the edge is hard steel and the body is softer. When you etch a blade with different hardnesses you can get a nice line at the border between each hardness. This is what I was referring to earlier, the hamon. The most instantly recognisable example of this is on a traditional Japanese Katana:

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This is a random image from Google, the hamon is that wavy line just behind the edge of the blade. The hard steel is paler. One of the main things you need to get a good hamon is the right manganese level, and I think my file wasn’t quite right (or my etching was a little poor). You can just about see the hamon I got on the edge of the blade:

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My one is a bit like ripples in water, I may have knocked the oil tank as I quenched the edge. Still looks pretty cool though.

Next up: Engraving and inlay on the blade! I will try to take more step by step photos.

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Making a File Knife Seax pt.1

As I like to have little projects to work on, especially ones where I get to try out new techniques, I have started making a small Anglo-Saxon styled file knife. What is a file knife you ask? Well, its pretty simple, its a knife made out of an old file. Its how a lot of knifemakers begin in the trade as files are the most easily obtainable source of high carbon steel. Very high carbon usually, which is great for making a knife with a really keen edge, but it also makes the metal a bit more tricky to work as it is much harder and more brittle than lower carbon steels. I like to make them every now and then as one of the first steps towards serious knifemaking is to buy named steel in bulk as it is then much easier to get a consistent and reliable hardness. File steel varies enormously and there is usually no chance of finding out exactly what steel you are working with so it can be a bit of a leap of faith when you come to the heat treatment phase, it is all to easy to mistreat the steel and end up with the blade you have slaved over for hours snapped into pieces.

The first thing I did was chuck it in the forge and heat it to a medium red glow to remove the previous heat treatment. If “medium red” is a bit vague (and it is, the colours are almost impossible to describe) you can hold a magnet to the steel at intervals. As soon as the magnet ceases to be attracted to the steel, pull the file out and put it to one side to cool slowly. This will soften the steel so that it is much easier to work and doesn’t destroy all your abrasives and grinding disks. It is possible to work it in its original hardened state, if you keep it cool you can grind out a blade whilst keeping the original heat treatment. This would make for a dead sharp and hard blade but is tricky to do and the blade would be prone to snapping as the raw file steel is very brittle. I like to soften them and then risk re-heat treating as it is much faster to rough it out this way.

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This is the file I started with, I picked it up at a boot fair for about 50p. Its is really dull and rusty, but its a good length (about 9″) and as I will be making a stock removal blade, I need to consider the tang length as well as the blade itself. The tang is the bit of the blade that goes into the handle. A good trick here is to use the file’s tang as the end of the knife tang, so you can get as much blade as possible.

I marked out the profile I wanted onto the file in permanent marker, then cut it to shape with an angle grinder and started to grind it down into a wedge section. As I was excited I didn’t take any photos, ho hum, I’ll have to do another tutorial at some point. Fortunately I have a number of old files kicking about! Here it is after rough grinding and smoothing:

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I have chopped the point off to give it the seax shape, and ground it to have a slight reverse taper (fat towards the tip) as lots of historical seaxes had these features. I then cut the tang as at this point I only had the file tang. If I had done this sooner I would have had less grinding to do, but I am pretty experienced so it actually doesn’t make too much difference. If it is your first knife and you are going slowly, cut first:

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There it is, a perfectly serviceable seax blade in a high carbon steel. Historical? Hardly, the steel is too good. Cool?

Hell yes!