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Thread: Clay Recipe

  1. #26
    Cool topic and perfect timing. I used to host weekend hammer-ins down here at my place, but due to work schedules I haven't in a long time. This coming Sunday will the next. The topic is claycoating and hamon manipulation. I'm making quite a few test pieces that we'll be heat treating then looking at the effects on hamon. I'll be using several different clay mixtures, application techniques and quenching methods. Each test piece will have at least three different clay sections so the effects can be compared. It ought to be a lot of fun. If anyone is down near Bryan, TX and wants to take part, come on down, just shoot me an email for more info. I'll be putting everything together for an article in our TKCA(Texas Knifemaker and Collector Association) newsletter.
    Don Halter
    KragAxe Armoury
    Bryan, TX

  2. #27
    Join Date
    May 2005
    Location
    Montrose, CO
    Posts
    2,276
    I've used a couple of different furnace cements and a couple of clay mixes, too. They all work, but differently. I like the furnace cement that comes in a caulking gun tube- it's fairly fine grained, adherent, and plastic. It also lets me apply the coat and immediately start the HT, no need to dry it for overnight or whatever.

    The best clay mix so far is 1 part wood ash, 1 part ground perlite, 1 part charcoal powder, and three parts clay from my backyard. I've tried borax, with no really impressive changes, and I'd try yellow ochre if I had any on hand.
    "Where the spirit does not work with the hand, there is no art."
    Leonardo da Vinci

    "A little science estranges men from God, but much science leads them back to Him."
    Louis Pasteur

  3. #28

    Test Hamon

    Sorry,

    The lag between posting and the post showing up on the forum made me post twice.

    RK
    Last edited by Robert G. Kobayashi; 02-09-2008 at 11:28 AM.

  4. #29

    Test Hamon

    I'm constantly experimenting with hamon application and techniques.

    I almost always do my "experimenting" on strap (whatever that may be, in this case 1075 from Admiral Steel).

    Here's a couple of pics from my latest.

    Thanks for looking!


    Respectfully,

    RK



    Heres the photobucket link:
    http://s249.photobucket.com/albums/g...view=slideshow

  5. #30
    Join Date
    Feb 2006
    Location
    Rock Spring, GA
    Posts
    347

    So...

    Robert,

    Were these all the same recipe? And what was the recipe(s) shown in the link? It would be nice to have that as a reference for any further comparisons that might be shown in this thread by others. If we're gonna "show-and-tell", then let's be sure to tell which steel (which you DID), the "clay" recipe, application technique, and how it was quenched (water temp, pull temp, etc.). Maybe even how the steel was prepared for the photos (i.e. "sanded to 2000 grit and etched w/ FeCl").

    Just my opinion if we want to do apples-to-apples comparisons.

    Thanks,

    Shannon

  6. #31
    Couple things I wanted to drop into the conversation. First of all, it seems that pretty much everyone here gets much more involved in their clay recipes than I do...I fall into the furnace cement crowd. I prefer the black furnace cement for its fine texture, although I typically thin it with water and then re-thicken with the finest dry refractory I have around at the time; the black furnace cement has an almost tar-like texture which makes it a pain to spread out of the tub. I have used some of the gray furnace cement mixes with pretty good success as well, although some of them are quite grainy and make fine control difficult.

    As Kevin mentioned briefly earlier, there are a few different types of refractories out there that often get lumped under the heading "furnace cement" while having vastly different properties.

    -To my knowledge, actual furnace cement almost invariably comes pre-mixed in tubs. It is a chemical set refractory, and as such needs time to harden, but is extremely tough actually somewhat flexible until it is fired. In my experience adhesion is excellent during drying, heating, and quenching, but fairly easy to remove after the quench.

    -Satinite is a heat-setting firebrick mortar, but there are also chemical set firebrick mortars (these may be similar to furnace cement, but I have not used them). My personal experience with Satinite (often pronounced "satan"ite) on blades has been poor. Adhesion during drying and heating has been poor, and I have always had problems with it popping off one or both sides during the quench. The best part about Satinite is the consistency, thus "satin"ite.

    I have also tried some of the bagged refractories without success, which has led me to use the pre-mix furnace cements as the base of my coating for a couple years now. My personal view is that the most important job of the clay coating is to actually stick to the blade. If I want to achieve something special, I can make additions to the furnace cement. My experience has been that the worst failures in HT happen when the coating pops away from the surface either during the HT, allowing quenchant to contact areas that I intended to protect. In the worst cases this can cause terrible warping as one side of the blade cools faster than the other...and the hamon is poor to non-existent.

    Having said all of this, I should note that I have been writing down a lot of info from this thread, since the posts go into much more detail about the specifics of different materials/additives than I have seen elsewhere. I'm curious to see whether anything more comes out about the effect of the borax in the clay coat...?

  7. #32
    Join Date
    Feb 2002
    Location
    Lancaster, southern California
    Posts
    77

    Question Clay recipes

    I haven't done any hamon stuff yet, but I just thought I could add to the confusion. I was clearing out my shop so I could insulate it and run power all around and for some reason I looked at the ingredients in a jar of that heat stop stuff used to coat a blade while soldering the guard on. I don't remember the brand, but it was bentonite with 2 other chemicals added. Made be think about using it in a mix. Also, there was someone on another forum that said Koval knife supply once had some japanese clay mix for hamons that came from japan. He said he bought it all. And had great control of his hamons with it, and that he had it analyzed and it had hardly any clay in it, but wouldn't tell what was in it. Then he came to this forum and said that the mix was almost all rice straw ash with about 4% clay added. However he wouldn't post any pictures of his work. He said he used any type of straw that he could get since rice straw was hard to come buy. I looked into getting rice straw and during my reading I found out that rice straw is higher in silica then normal types of straw. Some one here said that they mixed some straw ash with satanite and didn't see any diffarence. But I didn't hear of anyone trying it like he suggested with only 4% satanite or clay added. What does this all mean! You got me. It only adds to the confusion and goes to show that there is an endless number of combinations when you take into account all the coating mixtures, steel types, heating temperatures, and quench's and quench temperatures. Now are we all totally confused.
    Tony G

  8. #33
    Join Date
    Feb 2002
    Location
    Lancaster, southern California
    Posts
    77

    Clay recipes

    Sorry, I got confused as to where I was. That was on Don's forum that the person said his recipe was almost all rice straw ash.
    Tony G

  9. #34
    Join Date
    Feb 2006
    Location
    Rock Spring, GA
    Posts
    347

    Of course we are all confused...

    Peter,

    Borax is boric oxide. At our temperatures, it is a very powerful flux. That is why it is used to de-scale steel for forge-welding. It also has a tremendous affinity for silica at our temps. It will help to fuse, or sinter silicates in a forge at our temps. The bottom line is that in very SMALL amounts, it can help keep the steel from scaling under the clay--less scale=less popping off from scale. But if it is in too high a proportion, it will make the clay mix too glassy--immerse it in the water at temp and it will crack (or even shatter) and leave bare spots. If it becomes too glassy, it will also have a high coefficient of expansion and crack from cold air, exacerbating the immersion problem. Also, if it is sintering and fusing, it is shrinking--at least somewhat--which also means cracking and falling off. All-in-all, it probably would not be as much help as potentially hurting the mix.

    I have to agree for the most part with your opinions on the different commercial mixes.

    And Tony, I believe the difference in silica content between rice and straw ash is negligible. The fact that it is silica (and quite refractory) is what is important as much as the physical structure of the ashes.

    What makes a good insulator? The physical structure as well as the material itself. Lots of air trapped between those ashes. Lots of insulation going on. I like straw ash...

    Just my 2 cents,

    Shannon

  10. #35
    Shannon, I guess I wasn't entirely clear in my post. I am pretty well aware of the properties of borax as used in normal blacksmithing, and had a guess at its use in a clay mixture. The reason that I find its use odd is that borax has such an amazing affinity for water, and this water does not come out through normal drying. The water will therefore be trapped in the clay until it finishes cooking out at around 900F (I think this is about right). I would think this would lead to more corrosion under the clay, not less, plus the steam coming through the clay seems problematic as well. During the absorbtion and release of the water (up to 10 H20 per sodium borate, I believe), borax also expands and contracts drastically. Once at temperature, I can definitely see how borax would help fuse the elements of the clay together...that is what flux is for, helping elements fuse at a lower temperature than otherwise.

    I have been using furnace cement for quite a while with good success, and have never noticed an issue with scaling or corrosion under the coating. If you are having issues with oxides under the coating, I would assume that it is a low-temp rather than a high-temp issue, since a well-adhered clay coating should keep oxygen off the surface quite nicely to begin with. This makes me think that it is the water in the clay mix causing the problems...maybe try adding a little baking soda (high temp de-oxidizer as a bonus, I believe) to cut any acids in the water or clay.

    Tony, I have a hard time believing that only 4% clay or Satanite would provide enough structure to hold everything together. My opinion is that folks who try to keep a "secret recipe" to themselves are either selling something or hiding something, and I don't like either one. That is very interesting about the silica content of rice straw, though.

  11. #36
    Maybe I dismiss this topic due to my limited experience but there are so much reasons to get a nice hamon: Kind of clay, thickness of clay, kind of steel, hardening temperature, kind of quenchant, quenchant temperature etc.
    Therefore I think, the "optimal" clay recipe is no guarantee for a beautiful hamon - the main thing is that the clay don't fall off during heating and quenching.
    Best regards

    Andi B.

  12. #37
    Join Date
    Oct 2007
    Location
    Northeast Oregon
    Posts
    69

    And the Runes glew Ocher...

    I have never used yellow ocher in my hamon clay but silica and iron oxide have played an important role in my clay. I use red pottery clay to get my Iron oxide and I crush firebrick to get my silica. I dont know the details as to why but it creates an extremely hard clay that adheres very well, throw in some charcoal and you've got a balanced breakfast.
    There is no knowledge, that is not power.

    -Ralph Waldo Emerson

    The coldest hour is the one just before the dawn.

  13. #38
    Join Date
    Feb 2006
    Location
    Rock Spring, GA
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    347

    Let me throw in a few things...

    I am on a business trip and using the courtesy computer at the hotel, so I am keeping this short--please don't think I am being short-tempered. Yeah, I am a sword-addict. )

    Peter: At our temps, even around 900 F, the borax is SUPER volatile. So the affinity for water, etc. is not that big of a point. At 900F, it is low enough to melt and begin fusion of the silicates, but the water SHOULD have volatilized. But I HAVE quenched a blade in which the thicker parts of the clay were still WET under the hardened, crusty parts. There is just SO many variables....it is hard to tell from time to time. For the most part, the addition of borax would serve WAY more to harden and make the clay coat more brittle than it would add any benefit for descaling the steel. IMHO.

    Andi B.--you hit the nail on the head. So many factors and variables. But maybe this thread will help everyone to tweak and develop their own clay recipe that performs and doesn't fall off--that is one of the biggest problems.

    MVandine--if you use red pottery clay, the yellow ochre is already there--just in its more rudimentary red iron oxide. The clay itself is also about 60% silica--as is the refractory bricks. So you are getting a lot of silica. The crushed brick and charcoal are filler that eliminates shrinking. Sounds like a great mix.

    Thanks to all those contributing to this thread.

    Shannon

  14. #39
    Join Date
    Dec 2007
    Location
    The Netherlands, The Hague
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    33
    *cough*Sticky?*cough*

    Greetings,

    Dexter Wessel
    ~The Sword is an extension of the arm, but don't pick your nose with it!
    ~The Sword will prove its worth to you, after you have proven yours to the Sword.
    ~Rock, paper, scissors... And there there is the Sword!

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