Reusing witness cones

[irenepots]

I need to refire a glaze load and am wondering if I can leave the same witness cones in it for this second firing, which will hopefully get up to the right temperature once I change the cone offset.   I think it should work, but I'd like some  opinions.   The lowest cone only bent a bit so they have a ways to go.  Thanks for your help!

[Hulk]

Good question!

Are you using a cone pack on each shelf?

...any road, you might add a new target cone - right next to the used target - and see if they droop the same; my guess is they would, however, haven't tried/tested that.

I want to know what happened on each shelf, still dialing in loading - size, mass, position, staggering half shelves, etc. - to get evener heat work top to bottom, also want to know if an element goes south, hence cones at each level.

[CactusPots]

This is a question I have wondered about.  Here's how I always explain it.  A cone measures time and temperature as a speedometer measures time and distance.   If so, then does witness cone accumulate say 10 points and fall?  Or does a component of the cone trigger the next?  Would 1400 have to wait for 1300?  That would have to be the case to reuse previously fire cones, with accuracy.   Nothing would happen until we reached the previous maximum temp.  I'd like to run a test.  I'm done bisqueing until next load.  If someone would try a cone 10 cone in a bisque, then refire to 10, that would be the test.  It should be right along side a normal 10.  Maybe someone has already done this and can confirm or deny.

[liambesaw]

I've reused cone 04 witness cones that didn't bend, seemed fine.

[irenepots]

OK thanks everyone for your prompt responses.  I'll leave them in and add some new ones and let you know how the experiment goes.  I'll  be sure to mark them so I know which are the old and which  the new ones.  I use the free standing cones, I think they're called self-supporting.  Thanks for your input!  I'm going to run the kiln overnight.

By the way, where exactly is the cone supposed to hit for it to be that measure of heat and temp that matches what it's calibrated to?  I can't seem to find that info.  More thanks......

[CactusPots]

My call is that the cone bends to 3 o'clock.  The point would be 90 degrees from the shelf.  Anything between 1 o'clock and 3 would be a "soft" 6 or 10 or whatever.  Past 3 o'clock and not touching the shelf would be a "hard" cone.  Using witness cones, it's always good to use more than one set.  Say one high in the kiln and one on the bottom. 

[liambesaw]

The tip of a self supporting cone is supposed to be level with the top of the base.  The box has that info.  It's the front of the red circled ones

[liambesaw]

Here's a better shot, aim for the middle one:

 

[Mark C.]

The heat should alter the cone reading even if not bent-but a test is in order for sure to know for sure.My guess is its off a bit from the erarlier exposure to temps

[irenepots]

Thanks for your answers.   Looking on the box is not something I ever thought to do.  Duh.

Since this is my first glaze fire since changing all the elements and the relays, I have cones on each half shelf.   The bisque firings ran pretty much the way I expected so I fired the glaze load as I normally do.  I thought if anything it would be running hotter since the parts are new, but it finished a little low.    The kiln just shut off so I'll  get results tomorrow and let you know if the set from the first run and the second run look the same.  Thanks again.

[Hulk]

Hi Irene,

"By the way, where exactly is the cone supposed to hit for it to be that measure of heat and temp that matches what it's calibrated to?"

Here's the Orton chart and some explication as well:

https://www.theceramicshop.com/content/457/Orton-Cone-Chart/

When temp is rising slower, cone bends at lower temp...

[Bill Kielb]

14 hours ago, CactusPots said:

This is a question I have wondered about.  Here's how I always explain it.  A cone measures time and temperature as a speedometer measures time and distance.   If so, then does witness cone accumulate say 10 points and fall?  Or does a component of the cone trigger the next?  Would 1400 have to wait for 1300?  That would have to be the case to reuse previously fire cones, with accuracy.   Nothing would happen until we reached the previous maximum temp.  I'd like to run a test.  I'm done bisqueing until next load.  If someone would try a cone 10 cone in a bisque, then refire to 10, that would be the test.  It should be right along side a normal 10.  Maybe someone has already done this and can confirm or deny.

Hmm, cool idea. Most of the heatwork is done during the last 250 F of the firing. 250 F is several cones so depending upon when your kiln stopped it’s hard to predict. Cones are basically made of glaze and fired approximately six cones over their rating. Grind up a cone four cone and apply it to something at cone ten it Is glaze.

great idea though,  I’ll have to bisque a couple and try your idea. 

As far as reusing, just use new cones.

[neilestrick]

I read somewhere official a long time ago that if you've gotten with 3-4 cones of the actual cone, you should not reuse them.

[Babs]

I stick my glaze cones into clay and bisque  before using in a glaze firing. I was taught this many moons ago.

So I guess that at least I am consistent with the effects on all my glaze firing cones.

This would be as Neil states above.imo

[CactusPots]

That's one (of many) I've never heard of.  What is the point of bisque firing glaze witness cones?  I guess I always have single fire in every glaze load as my cone wads are green.  Sometimes not even dry as I just put them together the night before.  I've never had an issue with doing it that way.

I think my next glaze fire I'll try to refire some cone packs.  I have some 11s that never moved.  I'll get as precise a measure as possible and see if there's a difference with the normal ones.  You guys do get me thinking. Thanks

[Babs]

Exactly.

My glaze firing is rapid compared to my bisque. If any moisture in my clay wad base of cone pack or doesnt like the rate of firing, the clay wad cracks/ explodes from moisture content so I just chuck them in and bisque fire them....old dog here could learn a new trick but why?

I have winged it in the past and have had the wads shatter..so no big deal to prefire them.

Of course I dont do this with my bisque ones:-//

[curt]

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).

[irenepots]

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!

 

[Bill Kielb]

Thanks for sharing! So it appears however much heatwork was done previously (only in about the last 250 degrees of firing) is cumulative as the cone itself has started to mature. I love when things line up with the theory! So it’s hard to know the previous amount of heatwork in the last 250 since it failed .............. so......... always use new cones for accuracy.

thanks!

[Pres]

Yes, theory confirmed. Logic does say that as a cone measures "heat work" not temperature that using cones more than once is problematic or inaccurate. I have never reused cones as it only takes a tad of time to change up. However, most of my firings do not get interrupted, excepting for one in a thunderstorm where the transformer was hit!

Any more, I am better than close with heat color, especially when doing bisque. Glaze wise, knowing heat color does prepare you for shut off time/timing.

 

best,

Pres

[Hulk]

Good test Irene, thank you!

[curt]

Bill,   

Given melting temps and eutectics of the materials in the cones, I suspect heatwork is starting well before the last 250 degrees (Fahrenheit?) of firing, particularly in the case of mid fire or stoneware temps.    Do you have a reference on this?   However, if you are right, cones that have not gotten to within 250 degrees should be identical to brand new cones (say, in a failed firing where the kiln was shut down well before reaching top temp)?  I guess this would be a very testable proposition...

Did get me thinking about whether or not these same results would hold for bisque cones which we might be tempted to reuse?   Will have to save some underfired 04 0r 05 cones cones next time the situation arises!   

[Bill Kielb]

Likely so. Interesting observation. Cones are basically glaze . A cone six cone is 0.3 K2O, 0.7 CaO,, 0.6 Al2O3, 6 SiO2 which is a bit high with respect to the glaze. It likely should represent the melting that has taken place .......... I think! 

Not sure I think you have a reasonably sound theory. If the failure took place before the last 250 degrees of the firing then likely no effect, but the unknown is always how much of the firing took place in the actual relevant heatwork zone.

I like your theory and believe there is something to this.

[Bill Kielb]

10 minutes ago, curt said:

Bill,   

Given melting temps and eutectics of the materials in the cones, I suspect heatwork is starting well before the last 250 degrees (Fahrenheit?) of firing, particularly in the case of mid fire or stoneware temps.    Do you have a reference on this?   However, if you are right, cones that have not gotten to within 250 degrees should be identical to brand new cones (say, in a failed firing where the kiln was shut down well before reaching top temp)?  I guess this would be a very testable proposition...

Did get me thinking about whether or not these same results would hold for bisque cones which we might be tempted to reuse?   Will have to save some underfired 04 0r 05 cones cones next time the situation arises!   

Maybe,

An interesting calibration of Orton cones is to fire at 108 degrees per hour for the last 250 degrees and your cone magically bends at its 108 degree chart temp. Prior to that it’s hard to accumulate relevant heatwork. That is why   Firing to cone 5 + 20 generally works out to cone six. If you ever tried to fire at cone 3, you realize the hold time becomes ridiculous  and eventually ineffective. Firing to 04 (bisque) likely has almost no effect as the glaze in the cone can only be sintered so quitting at this point likely has no effect and folks often throw their glaze cones in their bisque fire presumably without effect.

Looking at  bisque cones they behave pretty much identically to that of others and simply have iron and boron added but still respond identically in about the last 250 degrees.

fascinating!

[curt]

Bill do you (or anyone else) have a table of the chemistry for Orton cones they could share?  I only have an old one for Seger cones, and although they are similar I know that there are slight variations.  

I also read on Orton’s website that there is other stuff in Orton  cones (eg organic binders), and possibly many other additions beyond the basic ones(eg, quite possibly some Frits?), so they are likely a bit more complex than just the standard raw glaze materials we use.  Point being that all these ingredients are designed to ensure that Orton cones always fall when they should.  And no doubt they are not intended by the manufacturer to be reused Lol. 

My point earlier was that it is highly likely that the materials in a cone are undergoing heatwork well before the cone starts to deform.  More specifically, I believe that the “relevant heatwork zone” (for our purposes here) is far greater than just the last 250 F.   Boric Oxide, (which was used in Seger cones up to cone 6, and is still used in some Orton cones?) starts melting at 300 Celsius, and is fully fused at 700 C.  The potash-alumina-silica eutectic (eg, as found in a frit) softens (is no longer a solid and begins to move) at 870 C.  Just because the cone is still straight does not that mean dramatic changes are not taking place inside of it!

And, as you point out, the fact that time and temperature ARE to a small degree substitutes in heatwork, somehow confirms that, while we may never be able to soak a cone 6 down at cone 3 temps unless you hold it for an incredibly long time, some kind of  heatwork is still taking place on that cone.

Lastly, I would say that all these observations should also generally hold true for the bisque-level comes.  In particular, if they have boron, I would suspect that there is much more going on in the cone than just sintering (which is more of a clay particle issue?), which means that they are also accumulating heatwork effects well before the last 250 degrees. (Even if they aren’t bent at all)

Rockhopper, to borrow from an older thread on this topic, cones are just mile markers along the firing highway, which have no relationship to the particular kind of car you are driving.  Hence they may or may not reflect the heatwork your pots may have received, only your pots themselves will know this.  Also, the stop-start process of reusing a cone may add an extra dimension of variability to the whole heatwork process (eg it is easier to re-melt a glass than remelt raw materials) which we really haven’t discussed here but which is probably also relevant for your pots.   Kind of an interesting idea though.