Project Badgermascus – Interlude 4 – New Tools

I have decided to make a sheath for the knife, but since the blade and the fittings are quite fancy, a plain leather sheath would be unbefitting. So the time has come for me to learn some fancy leatherwork. As you know, I am quite fond of making my own tools, but this time around I have decided to bite the bullet and buy some basic stuff for starters.

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These are really just the basics – a swivel knife and six basic stamps, a beveler, and a groover. The cheapest ones there were to find.

I will surely make some of my own tools in the future, but these should, hopefully, suffice for a start. They do not allow me to make anything that cannot be done with the tools that I already have – but they allow me to make those works much easier, more consistently, precisely and quicker.

Now I am going to cut up an old leather handbag and test some design ideas.

Project Badgermascus – Part 9 – Almost Done

The knife is done about 95% now. I have peened and ground flush all the pins on scales without some major failure, although there did appear one tiny crack near one of the pins ‘sigh’. I have sealed the crack with super glue and sanded it over, there is nothing else that can be done about it.

I did not do a very good job at the pins, I must say. I think the mistake that I make is leaving myself way too much material to move, which leads to a lot of problems later on. I must remember that for 3 mm pin it is quite enough to peen less than 1 mm material into a recess just 0,5 mm deep. It is not as if the pins need to hold extra-strongly.

But, it is done and it is what it is. I applied a little bit of patina to the pins. Not to make them black, just to make them ever so slightly aged. Funnily enough, the patina has highlighted some of the imperfections – and that made the whole assembly to look actually better. Only you must forgive me for now for not revealing the whole knife yet. There is still a lot of work to do before I consider it publication-worthy, do not expect that very soon.

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I am thinking now how to best seal the surfaces and the patina. Either beeswax, or drying oil. Or both. Any suggestions? I have zero experience with patina on metal jewelry, which essentialy is what this is.

Project Badgermascus – Part 8 – To Peen or Not to Peen…

Today was very stressful, although I did not, in fact, do too much work. But I was agitated about it so I procrastinated a lot, putting off each step for fear of mangling the work and losing a lot of progress. That will also be the case tomorrow.

Today was the day of gluing the scales to the tang. And because I wanted to peen the pins from the beginning, I also had to prepare for that.

For I lack proper ball-peen hammer for this kind of job. I have a wide variety of cross-peen hammers, but only one, big, ball-peen hammer. And that is way too big and chunky for 3 mm brass pins. They are not sold in any stone shop around here, and ordering one online would again put me in the age-old problem – is it worth buying something if the shipping costs more than the product?

So I have to make do with my smallest cross-peen hammer and a few thingamajigs that I have made myself to make the job easier and, hopefully, better.

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Peening pins in bone is kinda dangerous. Bone is hard, but not particularly strong and it can easily split. To try and reduce the risk of splitting I have therefore pre-peened one side of each pin before assembly, so the pins are shorter and thus less likely to bend when I am peening the other side. To make a better job of this I have taken a piece of mild steel from a failed attempt at burner diffuser and I drilled in it 3 mm hole, chamfered to about 5 mm recess on one side. Then I held the pins in a vice and peened one end into this recess.

The second tool that I have made is from an old hook-nail. It is very old and therefore good medium carbon steel, hardenable, although not to the highest degree, and very tough. If the tool works, I am going to carburize the surface and quench it.

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First I have cut off the hook and the tip. Then I have center-punched the center of the square where the tip used to be and dished it out first with a 3 mm bit and then 7 mm bit in a hand-held cordless drill. Then I put a big diameter ball burr for die-grinder into the drill and rounded the inside of the dish and I ground the edges round with a file. I have tried it and it seems to work well when used after the hammer for the final touches on the edges. So I hope to get nice round peened pins tomorrow.

With that done, I have also repaired one of the scales – two holes were a few tenths of a millimeter off so I could not put the pins comfortably through all holes. Not a big problem, I have filled the two holes with quick-curing epoxy mixed with bone dust and drilled them new. You would not notice there was a mistake there if I did not tell you about it.

Then I was ready for the job that I was putting off – the glue-up.

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I have used slow curing epoxy, with work-time 1,5 hours, instead of the 10-minute one that I have used previously for kitchen knives. The reason for this was not only to reduce stress and the possibility of a complete fuck-up, but also the fact that this simply could not be done quickly. Mixing the epoxy, slathering it over the tang and attaching the pins and the scales was simple enough, but after that came the difficult part – to clean all the squeezed-out epoxy from the fileworks. I have used first small pieces of kitchen towels soaked up in denatured alcohol to wipe out the biggest excesses and then a toothbrush soaked in the same to tease-out glue from al the nooks and crannies. I do hope I have made a good job because there is no way back now except either take it as it is or to drill out the pins, smash and grind out the bone and start with the handle scales all over again, which would not be fun at all.

Project Badgermascus – Part 7 – The Pinkening

For the next attempt at the patina, I had to think of a more fool-proof way to mask the areas of the assembly that are not allowed to come in contact with the chemical solution. I have used plastic packaging tape in the past, so I tried it this time. But the one I bought this time is extremely difficult to take off because the glue is too strong. That makes it also difficult to apply tightly around the blade since once it gets stuck, it cannot be corrected. And, the masking around the filework was a major headache-inducer, there the tape was totally insufficient.

So I needed something that is resistant to water and water-soluble chemicals both acidic and basic, hot and cold, something that will show me clearly what is masked and what is not, something that can be applied with high precision and good adhesion to complex surfaces and simultaneously can be removed easily later on without damaging the patina.

And after some thinking, I did come with a solution that worked really well. I made everything pink!

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That is the cheapest nail varnish that I have seen at the local drugstore (2,-€ per bottle). Afterward, I have added the packing tape on big surfaces, but I think it was unnecessary and just me being overcautious.

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I proceeded to make the patina on brass fittings by alternating between acid bath (HCl, very diluted) and polysulfate bath (with occasional brushing with a soft brush under running water) until I have received a color that I was content with, which is sort of metallic blue/brown/dark gray, very similar shade to the oak-tannin patina on steel.

Cleaning off the varnish was a bit of a hassle and used up a lot of paper towels and acetone, but the important bit is that it could be done, could be done well (it was easy to spot uncleaned places) and did not scratch the patina on either the fittings or the blade. I will probably buy heaps of cheap nail varnish, it opens up great possibilities.

Project Badgermascus – Part 6 – Trials and Tribulations

I have spent both Monday and Tuesday finishing flattening, drilling, and fitting the handle scales and the brass fittings.

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First I have sieved some bone dust that I have collected through a fine nylon mesh (from pantyhose – I do not wear them, but they can be quite useful in the workshop, so I have indeed several in a drawer). I mixed then the bone dust with five-minute epoxy, filled the hollow back of the bones with it and heated it with a heat gun to about 70°C (not so hot you cannot touch it, but hot enough you cannot press your hand against it for a longer time, a hairdryer would suffice too for this particular task) for quicker curing and stronger bond.

After it completely hardened I ground the back flat again and proceeded to drill the holes for pins.

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Drilling the holes was relatively uneventful. Double-sided tape was very useful in holding the scale on the tang and the whole assembly on a flat piece of wood for drilling to avoid chipping of the bone on exit. Also, I have used blunted and overheated drill bits to hold the scales in place for a good fit and I did not mess up the job terribly. I did make minor mistakes on the left handle scale, but those should be correctable when fixing everything together.

With the scales drilled and fitted against the bolster, I proceeded to make the brass pommel fittings. That went really well, and everything went smoothly. Too smoothly you might say. I glued the brass fittings in place, peened the pins and ground, and polished them over.

That is where the problems started, and I must say – they are not all my fault.

The first problem was that the round stock I have used for pins apparently has different chemical composition than the flat profile used for fittings. Had I known this, I would not file them flush and I would leave them slightly proud of the surface (“admitted” instead of “hidden”). However, there was no way back once I ground them flush, so I was hoping they will get hidden under the patina.

But the patining did not go well too, in three ways.

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The first  – I have made a mistake – I have not masked the steel properly. I thought I did, but I just did not. And as one Czech rather rude but astute saying goes – ” myslet znamená hovno vědět” – “to think (assume/mean/guess) means to know shit-all”. So when I was giving the brass a nice hot bath to copper plate it, some of that bath leaked under the masking and copper-plated and etched the blade in some places too.

The second – the different brasses did not take copper plating identically, it was a lot more difficult to copper plate the pins than the rest. It took over an hour to do on the pins what took mere minutes on the rest (which exacerbated the problem with poor masking later on).

The third – when blackening, I have made the solution probably way too concentrated. It has covered the parts in a nice jet-black matt color almost instantly. But that color has completely rubbed off when I washed it with water and brush. I did not realize the true cause of this so I tried it two more times, but it just did not take, especially not on the pins, After the third attempt I thought I am done on the pommel at least, but it flaked off the next day again.

These mistakes are not catastrophic, but they are a major setback. I had to re-polish everything (done), re-etch with ferric chloride (done), give the steel new tannic-acid patina (in progress), and only after that is done to my satisfaction, can I again try to patina the brass.

However, I have to deal somehow with the pins now. They are ground flush already, but since they will not take the patina the same way the rest does, I must leave them visible. And that means probably leaving them polished and not applying patina to them at all. I will do that and then I will decide whether I like it or not. If not, then I will have to drill them out and either replace them or, if I bungle that job (which is very likely) to make completely new fittings. Either way, it is at least one day, and possibly several days, of work before I can progress further.

However, there did come one good thing out of this – I found two new recipes for black that do not require copper-plating the brass first. One requires hot-bath with ammonia (CuSO4+Na2CO3 – precipitates basic copper carbonate which after filtering and washing with water can be dissolved in hot water by adding ammonia), so it is a major stink and not exactly easy or quick. The second one works at room temperature but is rather caustic and dangerous to handle (HCl + potassium polysulfide). I will probably try the second one now, although I do not like very much working with caustic solutions, since my equipment, as you have seen, is not exactly suited for that kind of job.

Project Badgermascus – Part 5 – Handle Scales

Tomorrow you will get a break from this project, I promise. But today, the Great Flattening from yesterday has continued.

After some deliberations I have decided to try and go for fully blackened brass fittings. That means that the blade will be dark grey, and the fittings really, really dark gray. What kind of handle material should I use? Marcus has sent me a nice piece of stabilized spalted maple, but I do not think it is the right material for this project. Ditto, any of the dark woods that I have. I think the blade deserves the poshest material I have available – bone. I think it will provide a nice contrast to the dark metal.

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Which meant I first had to rough-cut the scales with a hacksaw, which is one hell of a job, let me tell you. Bandsaw or any electrical saw is a big no-no for cutting bone, this has to be done manually. Including pre-cutting he flat sides, before grinding them truly flat.

Thus I had to spend the whole working day with a respirator and my fingers are all sore now. Because the grinding had to be done manually too. Belt sander does work on bone, but it destroys belts way too quickly for my liking and as I learned in the past, these thin flat pieces would have a tendency to be dragged out of my grasp, increasing the risk of injury or bungled work. So flatstone+glue+sandpaper it was. Maybe after I build myself a disk-grinding attachment this work will be easier, but now it is not.

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The scales are ever so slightly bigger than the tang and thicker than the bolster now, and they will remain so. I do not intend for a flush fit, but for a proud one ( I have seen English-speaking knife-makers refer to it as “heirloom fit” although I was not able to find anything specific about it, so I am not sure that is the correct term).

The principle is the same in carpentry – whenever two surfaces join, you can make the joint either hidden or visible, but it should not be visible because you failed to hide it. So if you make it visible, it should be apparent that it was intentional. Like gluing in spacers, making the surfaces meet in a groove and not on a flat, etc.

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Today’s work ended in the kitchen, where the two rough-ground scales ended in a pot at 60°C for an hour or so with circa a teaspoon of washing soda and one spoon of washing powder in 1 l of water to dissolve and wash out as much of remaining fat as possible. In the end I have added a teaspoon of hydrogen peroxide to whiten the bones a bit, although complete whitening is not possible on these.

Tomorrow when they are dry I shall fill the hollows on the inside (where marrow used to be) with epoxy to make them flat. After that, I can start the remaining works, i.e. fit and polish the pommel, drill all the holes, and finally, the glue-up. We will see how that goes.

Project Badgermascus – Part 4 – The Great Flattening

Today I have started the work on the handle, starting with brass fittings. First I have cut four pieces of brass, two for the bolster, two for the pommel, and I drilled 2,5 mm holes in the bolster pieces. On the left piece, I have then cut M3 thread and on the right piece, I have widened the holes to 3 mm.

For pins, I am going to be using a 3 mm brass rod. I cut 4 small pieces and on each, I have made a bit of M3 thread to go into the left side of the bolster (and later on the pommel). The M3 threads are, strictly speaking, unnecessary, but I find they help with two things. First, they help to keep track of which part is left and which is right, so I do not confuse them at some point and make a false cut with a file. Second, fiting the two halves together is easier, because the pins hold fast in place and do not fall off when manhandling the assembly.

I guess these preparations should not take me too long. They took me over five hours. The drilling, cutting etc was not the biggest issue. The biggest issue was the tang. During polishing of the blade it became noticeably thinner, and because the polished area bleeds over to the tang, the tang was not flat anymore – it was a few tenths of a mm thinner at the bolster. So I went and flattened it on a stone.

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As you can see, the tang has relatively deep gashes cut into it with the edge of the grinding wheel. Those are there for three purposes – they reduce the weight, they provide a good grip for the epoxy later on, and they reduce the area that needs to be manually ground off when making the tang flat.

Even so it took me a lot longer than it should have because I did not have the correct sandpaper readily available. What you see here is green corundum, which should be used only dry and only for wood. I have to buy very coarse wet & dry sandpaper, but I keep forgetting and the coarsest I have in stock is 120 grit, which is not nearly enough for this.

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And this is where I am now. Next, I will polish and finish the front side of the bolster but not assemble it. Then I will make the handle scales, fit and drill those, and only after that is done I will drill and fit the pommel part. I have not decided yet whether or not the pommel needs a hole for a lanyard.

The way things are going, I have still quite a few days of work ahead of me.

Project Badgermascus – Interlude 3 – Blackness Achieved!

Kestrel mentioned some commercial blackening compounds containing Tellurium and that train of thought sent me down a path of thinking whether I do or do not have some chemical compound containing sulfur anions, which too react with copper to make a black color. And I realized that I do because a solution of polysulfide is sold as a common fungicide. It does not work on brass directly, but if that brass is first coated with copper, then it does work. So I did exactly that, and voila! It takes a long time, but it works.

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It is not pitch-black, it has a bit of bluish-grey tint to it, but under a coat of wax or lacquer, it would be a lot darker. I consider it a definitive success.

I am wondering whether it would be possible to make pictures on brass with different patinas. As a kind of colored etching process. I do not see a reason why that should not work.

Project Badgermascus – Interlude 2 – Practice Makes Perfect (Allegedly)

I want this knife to be special because the blade deserves it. That means not only patined fittings but also decorations. So I have decided to do some filework – definitively on the tang spine and possibly the belly too.

However, I did not do a lot of filework yet. I did some, but that was twenty years ago and not only was it rubbish, but I have also already forgotten everything I learned back then.

So I am in this conundrum – I really want to make something I know I am not good at making. So I have decided to do today a practice day. I took a piece of mild steel, ground it to roughly the thickness of the tang, straightened it and I went on to figure out the hows and whats.

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What you can see here from top to bottom is a progression both in time and (I hope it can be also seen) in quality. The top one took me over two hours, the last one under one hour. Whilst the photo magnifies all the little imperfections to an unreasonable degree, there is still definitively a lot of space for improvement, some issues are still visible even at arms-length viewing distance.

I am bloody nervous about doing this because if a file slips, there is no way back. It was a huge problem for the first three patterns actually – establishing the first cut was the biggest issue I had. Files have angled teeth and they cut best when drawn perpendicularly to the edge. When you run a file at an angle, not only has it a tendency to slip and wander off, it also behaves differently when used left-handed as opposed to right-handed. Once the cut is established, all these problems are a lot less pronounced, but establishing that first cut precisely where you need it to be and at the right angle is a major PITA.

For the fourth pattern, I have finally found out how to best establish that initial cut. I have a beat-up knife made from an old saw blade in my workshop, that gets used for all those jobs a knife is good for but simultaneously not advised for. Like putting the edge on a piece of steel and hitting the spine with a hammer, to establish a cut line in the metal surface. Which is what I did here. Essentially like a center-punch for drilling. And just like center-punching prevents drill bits from wandering, line-punching prevents files from doing the same.

Now to beat my anxiety and to convince myself that I can do this…

Project Badgermascus – Interlude 1 – Sciencing How to Patina on Brass

So, the blade came out of the etch just spiffing, and giving it dark bluish-grey patina with tannic acid made it look really cool and mean, almost tacticool. But it is, of course, no longer shiny. Which made me think a lot about how to proceed from now on.

As you know, this is my first time working with damascus. Up until now, I have worked either with carbon mono steel or stainless mono steel, either with mirror or satin finish. Making the fittings on such steels from new brass, aluminium or steel is perfectly OK and does not detract from the blade. But making fittings shiny on this blade would feel, as we say in Czech, “jako pěst na oko” (like a fist punch in the eye). I do not have any spare damascus or mokume gane to go with it, nor the means and knowledge to make them, so what can I do? And the title, of course, gives away what I have decided to try – to make the fittings out of brass and make a patina on them.

So I went to my personal library, took out my favorite book “Chemistry for everybody” (published in CZ in 1990) and looked up the recipes in there. Then I looked a bit around the internet too. And then I went and bought a lot of pre-made commercial solutions for the job… NOT.

I looked up which chemicals that I already have could kinda-sorta emulate what the book says should be used for copper, brass and bronze and then I have of course performed a series of experiments to try whether I can make my own solutions. And the results are pleasing. And because there are a lot of pictures in this, the rest is below the fold.

[Read more…]

Project Badgermascus – Part 3 – Polishing and Etching

Well, now that I am down to only one blade, I can at least concentrate on it. So I did and today I have polished it all the way to 7.000 grit. There is still cable damascus on the very tip, but I have decided against making the knife shorter again and I will go with it as it is. The cable damascus is hardened and in composition similar to the 1095, so it will still cut and hold an edge well.

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© Charly, all rights reserved. Click for full size.

Now it will sit in FeCl3 for a while.

Initially, I have used still relatively concentrated solution (~1/10 dillution of solution for printed circuit boards) to see where the 1095 is. Now I am using a very diluted solution (~1/100) for the final etch, because etching this works a bit differently than etching damascus made from two kinds of steel where one has high nickel content. Why is that?

As a former chemist, I know at least a bit about what is going on now so I can show off.

The way etching works on carbon steel like this is an electrochemical process. The impurities gather during the forging process at the boundaries between the various steel layers and those impurities make the steel in those areas more susceptible to chemical attack because they create a sort of microscopic electric cells that attract the ions from the solution to the area. That is why in the etch with the more concentrated solution the cable steel quickly turned all grey and the 1095 remained all silvery – the 1095 is a mono steel with very few impurities uniformly spread throughout, whereas the cable, whilst being similar to the 1095 in chemical composition, has most impurities concentrated at the boundaries between former cable strands and at the boundary with the 1095.

In a concentrated solution, the reaction happens too quickly and can lead to pitting in areas with inclusions or more impurities. And a layer of various oxides builds up, leading to blotchy, uneven etch. That is ideal for revealing where the mono steel in the sandwich is, but not so great for showing the grain boundaries.

A diluted solution gives the reaction more time to attack the steel more evenly, but it of course also takes a lot longer. I probably won’t risk letting it sit in there overnight, but it will take hours. Allegedly the smiths of times bygone have used fruit (citrus, apple) juices, and it took a very long time, but I do not have several pieces to make a scientific study of it. Although, I might just cut the failed pairing knife into several pieces and perform an experiment….. Hm. I will think about it, that would be one way to get some knowledge and some fun out of a failure.

Project Badgermascus – Part 2 – More Failure

I want to stress up front, that none of these failures is Marcus’s fault.

So, what went wrong this time, I don’t hear you ask? Well, a lot, I am down one blade out of three.

I thought the pairing knife goes on really well, until 320 grit when I noticed a little perpendicular line on the spine. And It was not a line in the damascus pattern – those become visible during polishing, and that is very cool – it is a crack. I do not know when it happened. It might be there from the start, it might have happened when I was straightening the blade, it might have cracked due to the stresses involved during polishing – it is a very thin piece of steel after all. There are also some imperfect welds with inclusions in the piece, but this is not one of them, this is a crack.

Cracked spine. There is one more crack on the other side of the blade too. © Charly, all rights reserved. Click for full size.

No matter the cause, this blade is now irredeemable garbage, the only thing it could be reworked to is an awl,

I am going to finish the piece only as a show of what it could have been, but I am definitively not using any fancy materials for the handle. I planned on using stabilized maple burl (also a gift from Marcus), but now it will probably be just some random piece of birch or oak.

Works on the boot knife also did not go well. First I messed up the grind, bigly, but that was not the problem, that was still repairable, there was enough material that needed thinning out anyway. What was not repairable was the position of the cutting edge towards the blade’s tip. It turns out that I did not hit the 1095 at the center of the blank quite well. My grind was straigth, but the the 1095 in the center of the san mai damascus was bending ever so slightly to the left in this area. Had I positioned my grind just about 0.25 mm to the left, this would not have happened.

The darker cable damascus is reaching all the way to the cutting edge near the tip, where only the shiny 1095 should be.
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I have tried to re-grind the blade, but for that, I had to make it about 1 cm shorter and I  do not think it looks as well as it did before, it is too short and stubby. It should become a usable little knife, but I am not happy with it, and I am not finished yet.

Next time I will work with san mai damascus, I will probably first polish and etch the edge to see exactly where the cutting steel is. Too bad I did not think of that before.

All in all, so far this project has made me nearly cry several times and to want to quit knife-making because I am no good at it. When one spends several days with some work only then for all that effort to be for nothing, it has quite an influence on one’s mood.

Project Badgermascus – Part 1- Three Pieces of Steel, Two Kinds of Failure

Well, the title gives away that this article won’t end well. I am glad I did not start to write about this project right from the start as a series, I dislike having expectations build up only to be disappointed so I do not wish to do that to readers. And this is why I was also putting off work on this for so long – it was always a project with the potential of high reward – and high risk of failure.

You may remember that Marcus was so very kind and has sent me some damascus to play with, three pieces to be precise – one san-mai of 1095 and cable and two pieces of just cable.

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Here you can see the san-mai piece on the right already partially cleaned and ground, then in the middle is the smaller piece of cable with the scale cleaned off already with vinegar bath and on the left the big piece of cable damascus as it came. On that one, I had to grind the scale off with an angle grinder and after that, I have ground all the pieces to flat-ish until I could not spot any imperfections on the surface that might signify poor weld. This must be done since each inclusion or poor weld increase the probability of failure. It took me the whole last Friday to do this.

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With all the pieces flat, I could decide what kind of blade I would want to make out of them.

The san-mai damascus had one end of the bar rather ugly and it had an unseemly weld right in the middle, so making it into a long blade with hidden tang was not feasible. So I have decided to make it into a small drop-point boot hunting knife.

The smaller piece of cable damascus would look great as a dagger, but for that, it was too thin, so I have decided to make it into a pairing knife.

The big piece was just about the right size for either a big chef-knife or a chopper. I have decided to go for a chopper.

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I cut the excess with angle-grinder and then ground the outlines and bevels with 40 grit belt (which was a matter of mere minutes with my new magnetic jig, it works really well and I am happy with it). A draw-filing took care of all the perpendicular scratches and flattened the surfaces a bit and my new file-guide has proven itself very useful for making the shoulders flat and straight. It really does speed up the work when you have proper tools at hand. And in case you are wondering why the clothespins  – they reduce vibrations and therefore the noise the blade and the tang make when filing the shoulders.

Drilling the holes was a nightmare, I have destroyed three 3 mm drill bits, which is something I did not expect. But I have managed to drill al I need and with this, I was done on Saturday.

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Today I have decided to normalize the steel before quenching, so I have covered all three pieces with a thin layer of clay to protect them from decarburization, I have heated them above austenitic temperature and then put them into a bucket of pearlite to cool off. That is a bit slower than how normalizing is usually done (which is air-cooling for about an hour) but faster than how annealing is done (which is very slow cooling in the furnace for multiple hours). I have done this two times for the cable damascus (with straightening after the first cycle – the pieces warped, showing that it was a good call to normalize them) and after that, I have performed one more air-cooling cycle for the san-mai, because it is much thicker than the other two and has required more straightening.

I wanted to try differential hardening on the cable damascus so I have prepared a mixture of clay, perlite, and a tiny bit of water-glass as a binder and adhesive. I did not want to wait overnight for it to dry, so I have used first a heat gun and then the forge with low-fuel reducing flame to dry it quickly, thus the dark greyish color of the clay. No clay fell off, it did not crack either, so far it seemed all to work well.

Well, quench is when it all went wahoonie-shaped.

First I have quenched the small blade, in water. Unfortunately, it was so small that I have overheated it, and thus instead of the differentially hardened blade, I got a full hardened one. I have decided to not try again and I will finish it as it is, it can still be a good blade, just not with a hamon.

As second went the san-mai. I have quenched that first in sunflower oil, pre-heated to 100 °C, and then in water. It has definitively hardened and it seemed to be OK afterward.

Last I have hardened the big chopper. I have learned my lesson from the small blade so I have paid more attention to color, adjusted the flame, and took care to heat the blade to only just above the austenitic transition on the cutting edge and just below that on the covered spine. Then I plunged it into water, agitated, pulled it out, plunged it in again, and agitated it some more to cool it off below the martensite start temperature quickly enough for it to harden.

And during that second plunge, I heard a quite tell-tale “ping” sound. That was the moment I knew this blade has failed. I have scraped the scale and clay off with an old angle-grinder disk and took it in daylight to search for a crack. And I found it, right in the middle of the blade.

© Charly, all rights reserved. Click for full size.

I will polish the blade a little bit in order to see whether I have succedes at the differential hardening at least (preliminary scratch-test would suggest yes). However the size and position of the crack make it unlikely that the piece will be salvageable for a smaller/thinner blade, it is smack in the middle and it seems to go all the way through the hardened part right up to the soft material on the spine.

Today was not a good day, however from what I have read, this happens even to very experienced smiths. Even so, it sucks. I hope that at least the remaining two blades have no nasty surprises hidden for me.

I will have to buy some high-carbon tool steel to practice differential hardening some more.