I will share with you a proper analysis of the acquired data, but I just finished a little experiment and I am too eager to share the results.
Without too big analyzing of anything, it is clear at even a casual glance that polishing is the most time-consuming part of the job. It is also the most boring part, in my opinion, because not much can be done and the opportunities for a mess-up are numerous. It is necessary to go through the laborious process for fancy knives, like Ciri’s dagger, but for a kitchen knife without any ribs or facets it is a waste of time.
For over twenty-five years, ever since I read about the technique in ABC as a kid, I wanted to try a process that goes under many names, “tumbling” being probably the most known one. I have even mentioned the device for it in the article “The Handmade Dilemma” as a “polishing drum”. It is a technique that has been in use for thousands of years, literally – for example Bohemian Crown Jewels contain precious stones that were polished this way. And it has been tried and used for knife finishing both on commercial and hobby scale. All that it takes is having the polished things in a rotating drum where they tumble over each other, sometimes with the help of a polishing medium, sometimes without. A very simple machine, and had I lived by a stream I would build a water powered one years ago. Unfortunately I do not live near a stream and wind is too unpredictable so I am stuck with using electricity, and I have not got my hands on a motor with the right properties yet.
But I got lucky, my colleague has bought small toy tumbler for his son when he was little and they do not need it anymore, so he lent it to me a few months ago. As you can see, it is not big enough to hold a knife, not even a small one, so after I let it run with a few pieces of unhardened steel with very mixed and generally unsatisfactory results, it has collected dust again.
But here was the second stroke of luck – I have bought a slab of high-carbon tool steel and I started to make myself a set of better hardness measuring gauges than the impromptu ones I have made from an old saw blade. I have already ground and hardened these little chisels to HRc 62, and I only cleaned the two big facets and sanded them up to 150 grit – that is the grit up to which the grinding and polishing is relatively quick and the blade does not heat up too much. I was not intending to high-polish these, since that would be silly. But I remembered the lent tumbler and checked if they fit in – and the did!
So I chucked the blades into the polishing drum with a spoon of jeweler’s rouge and half filled it wiht crushed walnut shells, mixed it all up and let it run for one day. Bugger – it got blocked after unknown time and I only found out next day. So I started it again for one day. And the change in surface was remarkable. It was not polished, but the perpendicular sandpaper scratches were no longer visible and the surface has got a very nice satin sheen to it. But I like my blades mirror-polished, so I started it for another day. I took another chisel out and subjectively there was no change against the first day, so I assumed that this is as good as it gets (but I will let it run for one more day). But I also assumed that since there are no visible perpendicular scratches anymore, I can quickly buff it to mirror polish with the three buffing wheels that I have – and I was correct.
Here you can see four pictures taken with my digital microscope (courtesy of our quality department who tossed it away because they lost the installation CD – so I took it home and downloaded free software). Each picture represents a section approximately 10 mm wide in reality.