Time for a change. Building kiln 5

Ive settled on changing my kiln yet again. I have never really been happy with the way the flora kiln heated up. The kiln never reached good glazing temperatures. It may be the way the crossdraft was positioned from the firebox. Or it may be that the firebox was too small in comparison to the ware chamber. Not sure. The new plan is to build a new firebox ontop of a larger ash pit. I also will be making the new pot chamber smaller. I think if the firebox is a bit bigger and the ware chamber halved in size it should speed up the firing and hopefully peak temperature. After all, I was reaching higher temps in my volcano kiln. So here goes!

Wood kiln modifications to add crossdraft flame flow done.

Its been below freezing since Christmas here, so the snow and ice have built up alot outside. Though cold its beautiful too. Looking out my back door across the porch and backyard to the kiln barn.

I reworked the kiln chamber floor as best as I can to reflect Peters crossdraft suggestions. Im still thinking of ways to improve my ash pit which is undersized and difficuct to empty. The entrance flue vent to the chamber is now at the front while the exit flue to the chimney is at the rear.

Looking foward to trying this out as soon as I get the needed firewood gathered up!

Kiln science and improvements

A fellow blogger which I discovered searching over the internet on kilns a while back replyed to my open request for suggestions on my kiln. Peter shares a strong interest in wood kiln building and has inspired me to test the limits of my abilities. Thank you for sharing!

from Peter:

Hi Richard,

Attached should be your drawing of your kiln with modifications to the firebox. I probably haven't given enough detail in my modifications to show you all that clearly what could be done, but thought thisshould give you an overview of the sort of thing that you might attempt to sort out the problem. Not sure if the modification I suggest here would be possible with the current structure of your kiln, but do let me know what you think thus far.
There are other ways to go with this too. Turning it into an updraft could be easier to do. If you can put a hole through the top of the arch without causing it to become unstable, a length of pipe put above that for a chimney could result in a useful little kiln. Another way would be to rebuild the chimney alongside the chamber and feed into it from near the top of the chamber arch. This would also make a form of updraft kiln, but you would also have the benefit of being able to have an effective chimney damper built into the chimney above chamber height which would give more control than usual in an updraft kiln.

My bottle shaped updraft kiln will reach in excess of 2192 Fahrenheitin the lower hotter part of the kiln in about 5.5 hours. I recently read of a small round updraft kiln that would get to cone10 (about 2336 F) in 3.5 hours with wood stoking and natural draft (noblower).

Anyway, do keep in touch Best Wishes,

Peter

I cant wait to get to work on the modifications. Thank you very much!

Here are my possible modifications to the kiln firebox.

I am limited with my useable floorspace in front of my kiln so I am restricted to the footprint the kiln now sits on. I also have a low roofline above the kiln. I see how the firebox can be moved so as to give a cross-draft effect. I will have to see if it can be done. Thanks again for the input!

Diagram of my kiln flame path

Here is a picture of how I see the flame and hot gas flow in my flora kiln. Notice the pottery in the areas that achieve the salt glaze are highlighted in light blue. I am thinking of closing off the rear most firebox exit ducts into the ware chamber to force the hot gasses to travel across the lengths of pots more.
Any thought or suggestions are welcome. You may need to click on the picture to zoom in and see the details.

Salt glaze is a tricky thing!

Im pretty pleased with the pots and pieces near the flue. The salt worked its magic there. The front had almost no glaze effect. It may be that the chamber temps were lower at the front of the kiln. It may also be that most of the churning flames the salt vapors ride on were nearer the flue side. Either way it means I still havent mastered this yet. Back to the drawing board! Any suggestions? Im thinking of closing up the flueside chamber floor duct and expanding the frontside duct. My hope being that it will force the salt vapors to travel across all of the pots in the chamber, not just the rear most.

A two handled pot and a candlestick holder. I may put the holder back in one more time. Dont like the lack of glaze in the fluted areas.

I am now settled on some facts and limitations I have to abide by.

1. Creekbed clay is out for now as I cant reach the temps needed to flux it out. Nor does salt vapor seem to have any effect on it. Maybe the low iron oxide content in it.

2. Field clay from the Cutler - Burlington site has a high iron oxide content and salt glazes easy to a near black glaze.

3. Field clay from the Flora site has a somewhat lower iron content. It also has something else in it I havent identified that gives a grey green to it. It also salt glazes well if not quite as good as the other field clays.

4. I want to seperate the bottle glass I use as flux in the clay bodies by bottle colors. Dark browns, greens, and clears will be divided to help control the resulting colors in firing the clays.

Another first for me is that I logged time/temps this firing. I may be able to use this to work out some improvements in the kiln or my stoking methods.

I can say that I did use about 1/3 less wood this time than the last. It did come up to temp quicker as well. So closing off unused chamber space when firing a small load does have a positive time and fuel savings effect for my kiln.

First firing of the year.

I started about 9:30am and fired until 6:30pm. I cant wait to see how they turn out.

Heres an early pic with alot of steam flowing out. The pots were already dry, so all I can think of is the bricks I used to close off part of the chamber were damp. It burnt off and the temperature climbed after that.

And here is the pyrometer working its way up to temp. Still working out the best thermocouple placement to read from. Its doing better this time. I may buy a new K type one, the one I am using is a repaired one so I dont trust its accuracy to much.

I'll post pics soon of the results for you to see.