Reusing witness cones

[Bill Kielb]

Very interesting in my opinion.

Great discussion! I have cone composition to the flux and oxide level so from a component standpoint I do not know where they get their boron but Know how much if you will,  to illustrate Cone number origination to curious potters. This is relevant to me because I believe things melt based on composition, not necessarily individual melting points of discrete components, I will send you something you may find useful.

when we teach beginners about heat work or even try and calculate it for computer control algorithms it’s far easier to use the last 250 F of the firing where heat work has a significant effect.

The analogy for simplicity is we can put a pizza in an oven and try cooking it at 180  degrees forever and it likely won’t be a pizza. 10 minutes at 425 however and we end up with a master piece if you  believe the marketing on the package.

Clearly this is not precisely correct but does convey that the largest fraction of  where heat work occurs. And bisqueing something  at 04 forever will likely never make a cone six glaze be a masterpiece.

when we try and calculate accumulated heat work by computer, it’s far easier to use the Orton rate over the last 250 to bend the cone nearly perfect every time than try calculating through the entire firing.

I keep using the 250 number as the approximation, I would have to go back to the Orton documents for the exact number; however 250 degrees is stuck in my head as a convenient reasonable number.

Still  ...... fascinating stuff that may or may not be useful but very interesting. Give me a bit and I will send you  an interesting spreadsheet.

[curt]

Bill yes agreed interesting discussion, plenty to explore here.

1 hour ago, Bill Kielb said:

This is relevant to me because I believe things melt based on composition, not necessarily individual melting points of discrete components, 

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... 

 

 

   

[Bill Kielb]

7 minutes ago, curt said:

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. 

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.

[irenepots]

Great discussion.  Great Forum.