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curt

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  1. Like
    curt got a reaction from Pres in Cause of these cracks?   
    Yes now that is a cooling dunt.  Very sharp edged, sharp enough to cut you if you run your finger over it with a bit of pressure.  
    The earlier crack does not have anything like this.  The glaze knew the crack was there from the very beginning and simply pulled away from it throughout the firing, just like it was pulling away from ridges elsewhere on the pot (since it is pretty clearly a breaking glaze).
     
  2. Like
    curt got a reaction from Magnolia Mud Research in Cause of these cracks?   
    Yes now that is a cooling dunt.  Very sharp edged, sharp enough to cut you if you run your finger over it with a bit of pressure.  
    The earlier crack does not have anything like this.  The glaze knew the crack was there from the very beginning and simply pulled away from it throughout the firing, just like it was pulling away from ridges elsewhere on the pot (since it is pretty clearly a breaking glaze).
     
  3. Like
    curt got a reaction from Babs in Cause of these cracks?   
    Yes now that is a cooling dunt.  Very sharp edged, sharp enough to cut you if you run your finger over it with a bit of pressure.  
    The earlier crack does not have anything like this.  The glaze knew the crack was there from the very beginning and simply pulled away from it throughout the firing, just like it was pulling away from ridges elsewhere on the pot (since it is pretty clearly a breaking glaze).
     
  4. Like
    curt got a reaction from Min in SHIMPO wheel US voltage to NZ   
    I got a brand new Shimpo VL Whisper from the US a couple years ago, and directly on the circuitboard there is an option to change voltage from 110 to 240 by unsoldering a connection and resoldering it into another connection nearby.  Then you don’t need a voltage adapter of your own.   I did this and it worked fine.  Just need the physical plug adapter,  but make sure it is grounded!  For a while mine was not and I can tell you that is not good.
     Shimpo had instructions on how to do the soldering change which were able to be downloaded from their website if I recall.  Not sure if your wheel would have this option but worth investigating while you are figuring this out.
  5. Like
    curt got a reaction from Hulk in SHIMPO wheel US voltage to NZ   
    I got a brand new Shimpo VL Whisper from the US a couple years ago, and directly on the circuitboard there is an option to change voltage from 110 to 240 by unsoldering a connection and resoldering it into another connection nearby.  Then you don’t need a voltage adapter of your own.   I did this and it worked fine.  Just need the physical plug adapter,  but make sure it is grounded!  For a while mine was not and I can tell you that is not good.
     Shimpo had instructions on how to do the soldering change which were able to be downloaded from their website if I recall.  Not sure if your wheel would have this option but worth investigating while you are figuring this out.
  6. Like
    curt reacted to neilestrick in Clay Disposal/Recycling   
    Recycling clay as an individual user is very different than recycling clay for a business or entire studio. The pillow case or plaster slab method doesn't work on a larger scale. For individuals it's great, though.
    I think there are smarter ways of getting rid of slop than piling it up next to a pond and killing vegetation. That is not a problem with the clay, it's a problem with the person.
    I also think that the clay pit mine itself is far more damaging to the environment that the small amount that I throw out. And you would be surprised at how much gets thrown out during production.
    I don't think there is a right or wrong answer to this. It all depends on your situation and what works for you. 
  7. Like
    curt reacted to Min in Crash Cooling...Deliberately   
    There was an interesting article in Ceramics Industry from Larry Cam. His company fast fires from ambient to ambient temps in 3 hours or less, bisque, glaze and decal firings. He stresses how the LOI of both claybody and glazes are  important as are the schedules and heatsinks. He uses a deflocculated casting slip that is then press molded into plates etc. Full article here, including graph of firing / cooling schedule. I'm thinking that if you just want to crash cool and not fast fire the firing and cooling ramp could be useful. (There is a contact link to Larry Cam at the bottom.)
  8. Like
    curt reacted to neilestrick in Crash Cooling...Deliberately   
    It would all depend on what type of clay you're using, what forms you're firing, and how thick and evenly constructed they are. Lots of variables. Remember that raku firing uses very under-fired bodies, which handle thermal shock better than vitrified bodies.
    I've got a little test kiln that I can get to cone 6 in 5-6 hours, and it can cool fast enough to unload 5-6 hours later. It's so small that there's not much mass to cool down, though. My big kiln takes more like 32 hours to cool because of how much work is in there. Cooling it by pulling air though is a tricky situation, because it won't cool evenly that way. You can crash cool down to red heat without much problem, but getting through quartz inversion in a rush is tricky.
    If I remember correctly, tile companies that turn them around super fast are dry pressing the tiles under extreme pressure, which makes for a very stable form. Plus tiles have very low mass, and if they're doing non-vitrified wall tiles, they don't have to worry much about warpage.
  9. Like
    curt got a reaction from Babs in Who wants to see an explosion, look here!   
    Yes thought it might be Flir.  Was looking at them a while back.  They seem to be the most widely available in many different models.  Good to get a real user review!
    I imagine I will be able to point it at myself and get some idea of whether or not I should even bother venturing into the studio...
  10. Like
    curt reacted to Bill Kielb in Who wants to see an explosion, look here!   
    Sad but interesting true story.
    Early on, many many years past now my parents both became terminally ill at similar times. There were times that they were so frustrated and worn out that they refused to have their temperature taken, just flat out refused!  I was in my early twenties so sort of powerless to scold them and force them into it.  Fortunately I have always been a temperature junkie so back in those days I used one of the first non contact thermometers to measure the back of their necks while they ate breakfast. It worked like a charm!
    Man I wish I had that thing now, it looked like something out of star wars! I sure thought I had the coolest item at the time. Recently I looked online and I think I found one on Amazon for twenty bucks that lasts far more than 20 minutes on a full charge. I wish I would have saved that along with my really cool LED 7 segment calculator that had battery issues of its own, which replaced my sliderule! LOL
    Late Add, got curious and found this adapter for your phone. Nearly as good as what I have, Figures!
     

  11. Like
    curt got a reaction from Bill Kielb in Who wants to see an explosion, look here!   
    Yes thought it might be Flir.  Was looking at them a while back.  They seem to be the most widely available in many different models.  Good to get a real user review!
    I imagine I will be able to point it at myself and get some idea of whether or not I should even bother venturing into the studio...
  12. Like
    curt got a reaction from Bill Kielb in Who wants to see an explosion, look here!   
    Amazing Bill and great pics!  What kind of camera, software, cost, etc if you can?   Seems like a new toy I need for my studio for sure!
  13. Like
    curt reacted to Bill Kielb in Who wants to see an explosion, look here!   
    @CactusPots
    Yes sure,
    Infrared camera, lots of uses.  When water evaporates it cools the area so it’s real easy to spot it. First two pictures are of a large life size soldier sculpture drying. We waited until all the water was gone to ensure this did not fracture of explode in the kiln. I think this went to cone 2 (single fire)  to preserve the color of the underglaze.  It was fired on very flat shelves well grogged at no more than 200 degrees per hour. It was too large for an electric kiln so it needed to be rolled into the gas kiln and hand fired, but we have a pretty sophisticated graphic monitor that allows the user to see the firing rate and adjust as needed.
    Pictures
    1. Large Soldier sculpture still slightly wet ( not quite ready for kiln) 2. Large Soldier sculpture very dry (ready for kiln) 3. Relay terminal overheating 200+ degrees  ( time to tighten terminal) 4. Cup of hot coffee, cool handle and rim, +/-88 degrees (just for fun) 5. Ordinary leak in drywall (popular use)
     
  14. Like
    curt reacted to Bill Kielb in Reusing witness cones   
    Great fun!
    I like your Orton thought. Last thing I promise. Cones never fully melt so in essence they are about six cones higher than the glaze which of course fully melts (we hope). Grind up a cone 4 cone, it will melt like a glaze at cone ten. We never fully melt properly used cones, or rarely anyway. Still very interesting, simple and yet extremely complicated.
  15. Like
    curt got a reaction from Bill Kielb in Reusing witness cones   
    Bill yes agreed interesting discussion, plenty to explore here.
    Completely agree with this, and of course the whole notion of a eutectic (groups of materials which melt together at a lower temperature than any one of them alone) is a well established tool that every pot we make depends critically on!
    Boron is interesting outlier here because - all alone and on its own - it starts melting at 300 C and is completely fused by 700 C (see Digitalfire on Boric Oxide).  Basically this means that in any clay or glaze containing boron, the melt process is actually starting way before bisque temps.    And one thing we know about ceramic melt processes generally is that once one material starts melting, it tends to pull other materials into the melt more quickly, accelerating the melt process and the whole thing snowballs from there.   This is one reason (beyond the eutectics themselves) why the more fluxes you have the more likely you are to get a good melt. 
    I can see how your 250 F rule of thumb is quite useful - and reasonable! -  in the applications you are mentioning such as teaching concepts, automated control, overall heatwork evaluations, pizza cooking ( :-) ) etc, it is a useful approximation...  And no doubt that last 250 degrees is the most potent part of the heatwork process not least because, at that point, pretty much everything has been pulled into the molten material of the melt.  Only its own stubborn refractoriness - in spite of now multiple eutectics now going on around it - will save a given material it from being assimilated into the Borg, I mean the melt. 
    The twist in this particular thread is that by re-using cones we are accumulating heatwork over multiple heating episodes, rather than seeing the cones in the context of a one-shot, continuous-straight-throught-to-the-end process (which is the other 99.99% of the cases).   Since time - at some level and to some degree - does matter to heatwork, then if the melt process at the micro-structural level of the materials is getting going early (depending on materials, eutectics, etc.) , this would lead to a situation where every time it is used a cone is storing up heatwork, starting in many cases at surprisingly low temps.  And the more times we use them the resident heatwork ratchets up.
    Wouldn't it be handy to have an Orton research technician wade in about now??
    One other loosely related observation I will add is that I was always taught that bone-dry clay bodies do not shrink when fired to bisque.  After testing quite a number of clay bodies of all sorts I now believe this is incorrect (note to those of you who nest things when bisque firing).  Assuming this is true, why is there shrinkage from the dry to bisque stage?  Is it shrinkage due to pore and molecular water loss?  Is it shrinkage due to some kind of sintering loss?  Or is it to some degree shrinkage due to the beginning of heatwork amongst the constituent materials?  Just asking as I do not have a good explanation.   I can hear the voodoo drums starting up in the background now so will stop here... 
     
     
       
  16. Like
    curt reacted to irenepots in Reusing witness cones   
    OK here are my results.  The cones are 5.5,  6 and 7.  I was out of 5s.
    The sets of cones on the left of each pic are the original, reused cones.    On the right are the single fired cones.  The last pic is in the first category, but I neglected to add a new set to that lower left half shelf.  Do you think there's a significant difference?  It looks enough to me that I won't re-use underfired cones again.  I hope this info is helpful to you too.  Thanks for your input!
     




  17. Like
    curt reacted to Babs in Problems with dunting   
    Only on way up unless your kiln plummets downward or you are firing an almost empty kiln imo.
    An older potter was stunned when I asked her to put her red/  coloured  clay coffee mugs she'd made since day one pf her potting life, filled with water,  on a piece of paper overnight. We were having a conversation about how high we could fire before losing the attractive terracotta colour.
    She was shocked when the paper was damp the next morning.
    Never had any complaints in 50+ years of potting.
    ( after a few cups of milky tea  I wonder if it would seal??????) Do not follow this practice at home:-/
    However a mug left on the grandpiano or a vase of blooms , well....
    Not trivialising this matter just adding to conversation,  observations.
  18. Like
    curt got a reaction from Rae Reich in Reusing witness cones   
    I have reused cones a few times, including next to brand new ones, but can’t really tell you whether it works reliably or not.   It seems roughly good enough, judging from glaze results on pots, etc..
    But knowledge of the melt process tells me that even though a cone is still perfectly straight after firing, chemical change is nevertheless occurring inside the materials of the cone.    Boron for instance is/was used in Seger cones up to and including cone 6.  Now,  boron starts melting at a very low temperature, and thereby begins to pull other materials into the melt.    This melting / thermochemical change process may be significantly advanced at the micro structural level before there is any change evident in the physical shape of the cone as seen with the naked eye.
    The point is this:  If a cone is pre-calcined, then the melting process is pre-advanced.    All else equal this used cone will (could?) fall much earlier than a brand new cone right beside it.
    Finally, add to this the fact that most of a cone’s heatwork takes place in the first part of its bending (see Orton’s own pictures regarding this) and I think the conclusion must be that re-using previously fired cones could give very misleading information about the heatwork actually experienced by pots and glazes (ie, overestimate it).
  19. Like
    curt got a reaction from Bill Kielb in Homemade clay from dirt... lots of sand?   
    Some silt in your clay body is tolerable - but probably not more than 10% by weight.  Think of it like grog.  It is not really going to melt in the firing, and will form a large particle aggregate which acts like  gravel does in concrete.
    but, I think as Bill said you want way finer size if you are looking for actual clay particles in the classic sense.  Silt - even fine silt - does not behave like clay and is almost impossible to work with.  It just falls apart when you try to work it.  So it cannot make up the majority of your clay body.
    Even most Kaolins at 100 or 200 microns are mostly not plastic.  For plasticity and workability you need legitimate clay-sized particles - eg, ball clay or stoneware clay - in the tens of microns particle size.  Think maximum 200 mesh or finer and you will be starting to get there.
    OR, you can try to crowbar in some plasticity with small additions of bentonite if you are willing to make this adjustment.  But even that has its limits.
     
  20. Like
    curt got a reaction from Min in Porcelain plates breaking on glaze firing   
    Porcelain becomes pyroplastic (“melty and saggy”) at high temps.  Nature of the beast. The more cantilevered a form is the more likely it is to sag.  You can try firing a bit lower - say 10 or 15 degrees (but your glaze may not like this)  - or making your forms a bit thicker so they stand up better.  Or try another porcelain that is less fluxed.
  21. Like
    curt got a reaction from Magnolia Mud Research in Porcelain plates breaking on glaze firing   
    Porcelain becomes pyroplastic (“melty and saggy”) at high temps.  Nature of the beast. The more cantilevered a form is the more likely it is to sag.  You can try firing a bit lower - say 10 or 15 degrees (but your glaze may not like this)  - or making your forms a bit thicker so they stand up better.  Or try another porcelain that is less fluxed.
  22. Like
    curt got a reaction from Babs in Low Expansion Cone 10 Clear Glazes   
    This is a very interesting and worthwhile discussion, since we have all probably spent many hours agonizing over how to get a better clear glaze recipe. (I know I have).
    In my own testing, particularly with currie tiles, I have seen a few things:
    1.The most consistent and predictable crazing is because the simple overall amount of flux in a glaze is simply too high compared to the amount of silica and alumina in that glaze.  This happens particularly in the bottom left, or "C" corner of a typical currie tile, like clockwork.  The implication is that a crazing glaze is quite likely simply an over-fluxed glaze.  So the time-tested remedy of adding more silica or clay - or both - makes sense.  If you don't know what a currie tile is search these forums...
    However...
    2.  Simply adding more clay and silica in the same ratio quickly becomes impractical, mainly because glazes with too much silica and clay compared to fluxes simply become too viscous and do not melt or heal over well, mostly because silica and alumina are very refractory and stiffen a glaze, something Neil was alluding to above.  The extreme version of this problem, ie when there is far too much clay and silica in the glaze (or possibly the clay - see below), is crawling.  This effect is also very evident, particularly on the upper portions of a typical currie tile.
    One approach, if you have too much silica and clay and not enough flux), is simply to apply more heat, ie, fire higher.  And I think this is something that and and should be considered, in addition to changing chemistry, particularly if alkaline earth fluxes such as calcium and magnesium are available,   Their melting power is good, but it takes more heat to crack it.   Oh, and as long as you clay body will take it.
    Anyway, if you had to add something to adjust the chemistry, my tests suggest that glazes are much more tolerant of more silica than of more clay.
    3.  Once you are beyond the issues outlined in 1 and 2 above (ie, there is not too much, nor too little clay and silica in the glaze), the clay body becomes a very important factor.  Stoneware glazes all produce a glaze-clay body interface layer between the glaze and clay body when fired, where the glaze and the clay body "intermingle" at high temperatures, creating a new , third layer, which has chemistry of its own, distinct from that of either the clay body or the glaze themselves, but more like some intermediate version of the two.
    My take is that when glazes are thinly applied (as we like to do with clear glazes), this interface layer has a heavy influence on glaze appearance and behaviour, including crazing.  
    This interface effect appears most prominent in (relatively) heavily fluxed porcelain clay bodies, where the flux at the surface of the clay body appears to be augmenting the flux in the glaze as it intermingles, resulting in a somewhat over-fluxed final glaze chemistry.  The fine particle size of clay body materials in a porcelain body (and also of the materials in the glaze) is likely also playing a role in the glaze melt, as is the fact that we are usually trying to fire porcelain to porosity of near zero. 
    In any case, the thought is that all else equal, if you have a very fluxy, fine-particled clay body that you intend to fire to near-glass state, you can probably get away with even a bit more clay or silica addition than with, say, a coarse, groggy sculpture body (not that you would be putting clear glaze on such a body anyway?). 
    So, as Min suggested, looks like I am ending up in the same place as others here, but perhaps for somewhat different reasons.
  23. Like
    curt reacted to Min in Low Expansion Cone 10 Clear Glazes   
    @Lee S,to lower the expansion of the G1947U glaze I would be looking at the high expansion fluxes, ie the sodium and potassium that is being supplied by the custer spar. I would change some of the custer for spodumene to supply the low expansion flux lithia. There is room for more of both silica and alumina in the formula and will likely still get a good melt.
    Original recipe on the left, my altered version in the center, spodumene replacing some of the custer and a slight bump in the silica and alumina, then re-totaled to 100. (just for fun I entered Bill's recipe from above also). If this still crazes then I would increase the spodumene, decrease the custer further and increase both silica and alumina. Do you use glaze calc? 

  24. Like
    curt reacted to Bill Kielb in Low Expansion Cone 10 Clear Glazes   
    Stop crazing: Traditional way for gloss glaze is to increase Silica by 1.25 :1 clay so a progression of 
    1.25 sio: 1 clay
    2.5 sio: 2 clay
    3.75 sio: 3 clay
    and so on until crazing disappears.
     
    Don’t really like any of those glaze formulas actually all have R2O:RO in non durable range (R20 less than 2.0 can create issues). I don’t like to be less than 0.2:0.8 and gerstley not needed at cone 10. I am not a fan of calculated COE as well as the final melt will usually not be the calculated.
    something you can try that has decent chemistry:
    neph sy 28.99
    silica 23.19
    EPK 21.74
    wollastonite 26.09
    Flux ratio 0.23:0.77
    Alumina = 0.51 
    Good flux, wollastonite, should fire stiff and not run and can be tuned as above until crazing stops if necessary.
    I wish you were looking for cone 6, have used a matte and high gloss on all my low expansion porcelain for quite some time so I have those perfected.
    4,3,2,1 old standby pasted below from Glazy as well, again use crazing adjustment above as necessary

  25. Like
    curt reacted to Bill Kielb in Need help identifying glaze materials   
    Just break out the old mass spectrometer I think I saw one on eBay.
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