||[Mar. 3rd, 2003|05:14 pm]
Spent some time the last couple of evenings finishing up the polising of two tantos. I think I've discovered what works best for me for a good hand finish:|
Using the grinder, grind down to A6 Trizac (call it about 2000 grit), alternating scratch directions with each belt so that you're sure to get all scratches from the previous grit out (I usually profile and bevel with a 50 grit certamic belt, then go with 120 grit, A100, A45, heat treat, A15, then A6). Once I've got the flats of the blade polished, I go back with a water cooled grinder and put the edge on the bade, then work the polish down very carefully to within a few thousands of the actual edge. Any closer and with a powered grinder you'll overheat the edge.
Once I've got the power work done, I go inside and find a good movie or something to watch on TV, because this part is time consuming. While the Nipponese sword polishers are able to be fully focused on hand polishing a knife, I find I just can't focus that narrowly for that long on it.
At any rate, I use 3M graded microfine abrasives from this point out. I picked up a sample pack a few years ago and am still using pieces from the sample pack. I use choji oil as a lubricant (basically mineral oil with clove oil added for scent and color), and start with a 15 micron (about 600 grit) and work my way down to 0.3 micron (about a zillion grit -- OK, I think the math works out at about 25,000 grit -- this is the stuff used to finish hard drive platters, so it's pretty fine.)
At this point, it's pretty much a mirror finish, individual scratches can't be seen (if they are, I go back a grit or two and work them out.) I don't go to this kind of effort except on Nipponese style blade -- for regular blades, just buff it out, you get the same finish, but you won't be able to bring out a hamon or ji or nie if you buff. Buffing smears the steel around, while the hand polish removed the scraches but leaves the surface of the steel undisturbed -- opening a window into the steel.
(Digression) The Nipponese polishers use stones, mostly natural, in their polishing. The only reason I don't do this is that it's very, very time consuming and the stones can be unpredictable. As the natural stones often have irregularities, you have to know your stones at an intimate level -- which side is the softest, if there are any hard spots, what the pattern of scratches each one leaves, and so on. When you get to the finger stone level, you have to test and fiddle with each stone, back it with the right paper, thin it down to a paper thin sliver of stone, and carefully use them to put the final polish on the blade. If you press too hard, or not hard enough, or let the fingerstone dry out, or if the layer of polishing stone slurry gets too thin, you get a scratch you have to work out. Me, I use graded abrasives, guaranteed to be of a certain abrasive quality. The finish isn't quite the same, but until I have the time to spend the 10 years as an apprentice polisher, it will have to do.
The final step is to use nugui to darken the surface of the steel and bring out the various artifacts of the hamon. Nugui is, usually, made of some fairly common materials: black iron oxide, red oxide, some of the older formulas call for cinnabar (avoid avoid -- this is mercury oxide, and you don't want to fool around with mercury compounds.) Various vendors sell prepared nugui in powdered form, I have seen, but haven't tried, some of the prepared nugui already suspended in oil. To use the powdered nugui, I first grind the material very fine -- I've found the stuff as provided by vendors isn't fine enough, and a few minutes in a mortar improves the quality. Once ground, I mix it with choji oil and let stand, stirring occasionally, at least overnight, and longer is most likely better. Once I've lost patience with the stirring and let sit phase, I filter it through filter paper (ok, I use unbleached coffee filter paper, 2x thick), and collect it in a bottle.
To use, the nipponese polishers use a clean cotton cloth with a very fine weave. I've been trying and have had good success using lint-free optical paper -- the stuff used for cleaning eyeglasses, optical equipement, camera lenses, etc. Just apply a bit of the nuigi solution to the cloth or paper, and rub it back and forth on the blade until the blade is coated. Let it sit, I usually let it go overnight, then repeat. By reapplying every 12 hours or so for a week I get a nice dark finish that really highlights the activity in the hamon.
Well, I hope this helps someone out there. If you have questions, leave a comment.