[Clayart] pyrometer testing.

Robert Harris robertgharris at gmail.com
Mon Oct 25 04:49:12 UTC 2021

Mel, I'm curious as to how you figured out what temperature the cone should
fall at. (And therefore be labeled as "too low". My Orton cone charts give
three different temperatures depending on the rate of rise for the last
200F of the firing. (27F/hr, 108F.hr and 270F/hr). My firings are usually
around 60F/hr for the last couple of hours, which is in between the first
two temps given. (Cone 11 is given as 2322F and 2361F for the 2 temp
gains). There is no indication that the temperature difference is linear
(and I suspect it probably isn't). So I'm curious how far off your
pyrometers actually are.

On Sat, 23 Oct 2021 at 06:25, mel jacobson <melpots at mail.com> wrote:

> Colleen and I fired both of our stoneware kilns
> this last week at the farm.
> She fired the big stoneware and I fired the smaller one.
> I have done some gas plumbing changes to both kilns, adding
> a high temp regulator at the kiln end with a tee connection
> to both burners so they each fire the same, all the time.
> (much easier to chart as we can use the numbers on the gauge)
> We have added high temp regulators at both kiln's tanks.
> (jeff from the gas company installed them/ near 40 lbs of pressure.)
> The difference in firing speed and efficiency is amazing for both the
> big stoneware and the hard brick salt kiln.  We are now under 8 hours for
> the salt kiln and in the past it was always 12+.
> We used the digital pyrometer on the big stoneware, +cones of course.
> I used my older analog pyrometer and the infa-red gun.
> Some early results by changing pyrometers around and using the gun
> indicates the digital pyrometer as expected was low at cone 11 by almost
> 30 degrees. My analog was closer but did not give accurate numbers at cone
> 11.  I fired cone 11 flat, Colleen prefers cone 11 at 2 o'clock.
> For around 50 bucks the infa-red gun is a great helper. One has to turn
> down
> the pressure for a minute or so as you do not want back pressure flame.
> You have
> to get close to the peep and aim to the center of the kiln. At cone 9 the
> gun
> read 2321F. Damn close.  It too read low at cone 11 over.
> The best news for me is that all three pyrometers give very accurate
> readings
> during the firing. We know when to reduce, when to change settings etc.
> I have attached the analog pyrometer to my small kiln with all wiring
> stapled
> in place.  It also has a sign..."Do not move"  "EVER".  I have marked that
> dial so that when cone 11 is going over it hits a spot. dead on.
> Of course nothing takes the place of cone 9,10,11 for accurate firing.
> I am using one analog pyrometer on the electric bisque kiln. It sticks in
> place at 2000 but reads well for bisque temps.
> I have hammered three analog pyrometers and one digital. In the dumpster.
> When we have guests in firing, it was common for them to dig out my old
> pyrometers and have them reading the wrong numbers...so out they went.
> In talking on the phone to some heat engineers they all agree when
> measuring
> devices start to act up...hammer them. They do not fix. They all agree that
> digital is the best, with the infa-red gun as your back up. CONES WORK.
> as we all know, engineers work with very high tech
> industry with amazing perfection. They never mess with pottery kilns so
> we are always the last to know.
> And without doubt, all heat measuring devices are very fragile. I like mine
> attached to the kiln.
> mel
> ps, and remember, we as potters are often victims of what your propane
> dealer
> supplies. At times you must argue for more pressure.  It took a long time
> for
> me to become a trusted friend of "Jeff". He now "gets it".  but for many,
> kilns
> are running with house pressure and that means long firings. "often they
> do not
> listen as they don't understand."
> I bought $1500 of gas for the winter. and in the last week propane went to
> $2 a gallon. I paid $1.21, and it could easily go to 3 bucks. (last July I
> paid 92 cents.)
> website: www.melpots.com
> www.melpots.com/CLAYART.HTML
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