Dressing natural stones after flattening

Discussion in 'Hones/Honing' started by MrCrispy, Sep 11, 2019 at 6:03 AM.

    I'm pondering how to best finish some stones from the wild that I just flattened on a granite reference plate...and I am confused about some aspects of prepping stones where there isnt a known grit reference to target. Maybe I am over-thinking it?

    I have two nice Hindostans perfectly flat. They have very different characteristics, with one being quite soft, the other being harder. One horizontal strata, the other vertical. Harder stones it would seem would have a higher 'potential grit' than a softer one?

    It seems most people suggest to flatten 'fine stones' to 1200grit and 'rough stones' to 600grit.
    both of my Hindos just came off 220grit, and make a hollow ground sing with pretty different tones.

    When will I know that I am over-polishing the surface, and just dulling the surface layer?

    /confused
     
  1. Learn by doing and trying new stuff. What others do or say may not relate to you and your needs/experiences/scenarios.
    Me, I almost never polish anything past 600x on w/d, most only see a worn 400x Atoma.
     
  2. It's going to depend on the stone and your purposes. Very hard stones can be used in different ways by dressing them to a differing finish level. Softer ones can't be used this way very well, as they tend to quickly revert to whatever surface is produced during use as dull particles are ripped away.

    I would advise experimentation also. Start coarse and use the stone for a bit, see what happens. Does it quickly get a groove worn in? If so, it's a softer stone, and dressing won't matter much for very long. If not, try dressing a little finer and see what effect that has on cutting speed and finish. Go from there. All the experimentation may seem tedious, but with natural stones it's really the only way.
     
  3. Thanks for the input! I will keep working with them and make up my own test bed.
    I'd like a consistent test that doesn't use a blade, so I will keep poking around and do some testing on doing some testing. ;).
     
  4. This is the best use of Gold Dollars IMO... they don’t take or hold a great edge, but they can tell you how coarse or fine a mystery hone might be.
     
  5. SliceOfLife

    SliceOfLife Contributor

    If a Whetstone needs dressed, that's a drawback in my opinion. Really the only ones I've found that require this treatment are overly hard Jnats and some VERY old synthetics (barber hones). Even those are rare. I think people tend to blame an unpolished surface of a whetstone when something else is the problem quite frequently... also I recall MANY of the "foundstone" experiments having the property of cutting coarse after lapping and then not cutting at all after they wore in... making them unsuitable as whetstones. Most stones that make good whetstones are minimally affected by surface polish, because they have abrasive density enough that they act as a HONE, and not a file. If a stone changes significantly from polish, that means it's working as a file... and with whetstones, a file that wears down to uselessness quite quickly in most cases.

    Oilstones can use level of finish to adjust how aggressive they are, but it does require regular refreshing, albeit they tend to hold it MUCH longer than whetstones.
     
  6. Thank you. I am struggling to ask the right questions to get to the why. For conservation I am used to thinking along the lines of polishing and sealing surfaces to avoid oxidation issues. New to the world of interesting mystery hones, I catch myself wanting to 'pretty up' a stone after stripping the oil and lapping it. Soft or hard, I get the benefit of beveling the edges to avoid messing up blades when honing...that fixes a danger.
    I use a DMT 320 for cleanups and granite reference plate with 220grit wet dry for flattening.
    So, if I get what you are saying, the *'virgin' exposed strata* is the true stones cutting strength?
    Polishing it further can reduce the cutting strength but harder stones fit into that place in a progression naturally.
    I am very visual so this helps a lot.

    What do I lose if I took the approach to never touch up a stone outside the flattening process?
    I like a slurry when honing, is the DMT320 ok for this or is there value in cutting naguras to match?
     
  7. I am thinking of cutting 1x2x1/8 aluminum stock, setting a bevel, raking them 5x each direction, and marking them to match each stone. This way I can pull out a test next year or pass along the info with the stone if it doesn't fit my collection. I may be chasing my tail but I enjoy the test/analyze process
     
  8. SliceOfLife

    SliceOfLife Contributor

    Basically:

    If a stone is gonna be a good whetstone, it should cut fast no matter how much you polish it. This is because it has abrasives significantly harder than steel making up a SIGNIFICANT portion of it's makeup, regularly and consistently dispersed in mixture of materials the stone is made from.

    It should also wear fast enough (this doesn't necessarily mean fast... for harder abrasives like the garnets in Coticules, VERY SLOW wearing is ideal... for stones with more friable flakes of silica as the primary abrasive, you want faster wear) that the rate of abrasion doesn't continually change as the stone wears... cuts aggressively, then the abrasives wear, stone slows down, stone wears again, becomes aggressive, abrasives wear, becomes slow, etc.


    Because of this, a GOOD whetstone that is hard enough it would hold lapping scars of a size that would be problematic, is going to have so much abrasive density, that the tool will ride on the abrasives ABOVE the scars... Softer stone with already rounded abrasives? It's gonna wear in almost immediately under the tool and lose the scars. Basically, if a Whetstone shows a significant change in refinement coming off a 120grit DMT vs off 2k grit sandpaper... it speaks poorly of the whetstone... or the user (If you're grinding a razor with a ton of pressure into a 120grit surfaced extra hard Jnat and are surprised that it cuts coarser than it should... maybe get yourself an easier to use stone).


    That being said, the exceptions prove the rule. I've got CRAZY hard coticules that are definitely easier to use if polished... same for ultra hard Jnats. Thing is, these stones are of a type that straddles the line of what should be a whetstone and what should be an oilstone. The Coti's especially cut more like an oilstone than a whetstone when you get to extreme levels of hardness (even though I personally don't use oil with them).

    But as a general rule, it's VERY rare that I polish up any hone I plan to use with water except ultra hard Jnats and I consider that level of hardness a defect that I am accommodating by polishing up the stone, I don't feel it's a normal sort of maintenance that a top quality stone should require.

    And then of course there are ultra-fine oil stones, where the polish on the stone can definitely make a difference in refinement... but we're talking a whole different mechanism for how the stone works vs a whetstone.


    The long and short of it is, when I see guys doing sandpaper progressions on stones like Thuringians (very soft) or your average coticule (quite soft on average), or -even more pointless- high grit synthetics (these have such insane abrasive densities you could scar up the surface with an engagement ring and a razor would still ride right over the gouges on the pronounced abrasives on the surface, as long as you knocked any RAISED area's down before use).
     
    Last edited: Sep 14, 2019 at 11:37 AM
  9. duke762

    duke762 Contributor

    Although I like the idea of a reference, I think I'd use some kind of steel for this. I'm afraid aluminum would seriously load your stone. I won't let non-ferrous metals anywhere near my natural hones.
     
  10. Slice made excellent points... I’ve seen the DIY rock hunt work out well a few times for woodworkers but the successes I saw fell into 1 of 2 categories:

    Someone starts with known raw materials IE research novaculite deposits and go gather rocks there.

    Or someone studies enough geology to roughly recognize a silicate rich rock that’s got a better chance of working and then accept that you’re only going to be happy with about 1/8 of the stones you try out.

    There was a British woodworker I chatted with a few times who basically went to his local landscaping center and bought all his whetstones, so it can be done.
     

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