: JBaymore - Viewing Profile

In a true downdraft kiln, the exit flues are always located in the floor. Which often puts them below the "burner ports" or "inlet flues". So the answer is "yes". A lot of the studio type ceramic kilns have a modified downdraft circulation...... to get away with the construction of the horizontal flue breech below the working floor.

Take a look at he picture of the kiln floor on the lower right of this page to see the set of tuned exit flues in a true downdraft unit. Wheneve I can do a true downdraft for a client (a bit more expensive to build), I do so.... they fire better:

http://www.johnbaymore.com/page31.html

best,

....................john

This kind of analysis gets really complicated if you are asking this question in trying to do a "better or worse" kind of comparison. That was one of my key points in the NCECA presentation. Too many "green" statements are very narrowly focused....and often highly misleading. The "big picture" is the only real accurate answer when you take ALL factors into consideration. To do this requires experts to look at it all. And lots of time and study (and hence money).

First of all..... WHO is firing each type of kiln, and HOW are they firing it? Those two factors alone can have a huge impact on "the numbers".

For example, in teaching situations I have deliberately taken a specific gas kiln and set it up firing in what would be an "appropriate" amount of reduction. Then I measured the levels with an Oxyprobe. I then had other people come in and observe the kiln VISUALLY for a while to "learn" the level of reduction happening using all the usual visual, auditory, and olefactory markers that potters tend to use for this. They could even see the reading on the Oxyprobe for that part. I then had them leave the room, and I mis-adjusted the controls to put the kiln into oxidation. I asked them each to then come back in and adjust the kiln VISUALLY to match the prior original condition (but no Oxyprobe available to them this time).

When they SWORE the kiln was set "the exact same way"...... I'd check with the Oxyprobe. The readings were ALL OVER THE PLACE. Some of these people were students... and some were facutly with MFAs and YEARS of firing experience. Some people's settings would have produced less CO and less particulate C ...... and others produced more. (Yhis is also what people often get "surprises" when they open the kiln.)

WHAT is the kiln design? There is another HUGE factor. Some gas kilns have very really lousy combustion systems on them and very poor in-chamber mixing. Others are "state of the art". Each would provide different answers for you... and STILL would be tempered by WHO is firing then amd HOW.

Some wood kilns have very efficient aeration and mixing...and some are literally still 15th century technology. Each would priovide you with completely different answers. There is a noborigama in Japan that has full industrial scrubbing........ fires as clean as a whistle.


To generalize (which makes this answer wrong in 99 percent of cases), PM 2.5 and PM 10 for a wood kiln is significantly higher than for a gas kiln. But on the other hand if you look at a 30 year cycle period, wood kilns are carbon neutral if replacement trees are being grown while gas kilns are greenhous gas producers.

Periodic studio type electric kilns are HORRIBLY polluting when looked at in the "big picture". They are NIMBY units when people think of them as "clean". They have a chimney.... it is located at a centralized power plant. Centralized electric generation and transmission is very lossy.... inefficient use of fuel. Coal is contaminated with mercury. Those types of kilns are typically underinsulated. They are also small and have large surface to volume ratios... so the heat energy used to heat up the kiln structure as a ratio to the heat energy used to heat the wares is TERRIBLE. I could go on.

Name your poison.


best,

....................john

Should not make any difference at all.

best,

...................john

Here's the molecular formula for the glaze:

------------------------------------------------------------
Baily's Red Cone 6
Code Number:
=========================================

Custer Feldspar............. 46.60
EP Kaolin................... 4.00
Bentonite................... 2.00
Bone Ash.................... 15.00
Lithium Carbonate........... 4.00
Talc........................ 16.90
Silica...................... 11.50
Iron Oxide Red.............. 11.50
=========
111.50

CaO 0.33* 8.02
Li2O 0.12* 1.53
MgO 0.29* 5.10
K2O 0.11* 4.42
Na2O 0.05* 1.37
P2O5 0.10* 5.98
TiO2 0.00 0.01
Al2O3 0.21 9.23
SiO2 2.08 53.93
Fe2O3 0.15 10.41

Cost: 0.17
Calculated LOI: 4.44
Imposed LOI:
Si:Al: 9.91
SiB:Al: 9.91
Thermal Expansion: 7.19
Formula Weight: 231.58


Date: 2013-06-15
ID: Baily's Red Cone 6.XML

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Using Cooper and Green Limits...... it is slightly undersupplied in both alumina and silica. Alumina/silica ratio is pretty good. If you bring one up.... bring up the other too.

best,

......................john



EDIT: Fixed word "rations" to what it was supposed to be "ratio".

I'm not teaching at the college this summer........ so my plans......

Try to finally get the yard in shape here in June if it ever stops raining!

Finish getting pots made for a firing shortly.

In less than a week ... I'll be a grandfather for the first time. Go see my daughter and my new grandchild.

Packing up and scheduling shipping of work for some shows that are happening while I am away.

Headed off to Japan to work and study for the rest of the summer.

Get back JUST in time to deal with pre-start-of-semester faculty meetings and tuning up course outlines and content.

best,

.....................john