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.

Thinking smaller, getting ready for next firing.

Here are a couple more photos of some of what came out of the Christmas firing of my kiln.
The bricks are really great. The white one in front is one of my favorites.

The large tiles came out very well also.

I went thru alot of firewood last time getting the kiln up to salt glazing temperature. In an expiremental effort to speed up the firing and save fuel, I am reducing the chamber size to salt glaze my pots. I will let you know the results soon.....

All bricked up, waiting for the mud to seal the cracks. I also moved the pyrometer thermacouple probe into the heart of the chamber this time. I hope to get a more accurate reading from it.

Firing is set for sometime this weekend.

Christmas firing challenge and success

I had been planning to fire up my kiln on Christmas day for a week now. I wasnt sure I was going to be able to stick with it after I injured myself on my left hand on Christmas eve. After a trip to the ER and 5 stiches later, I decided to very carefully go on ahead with the firing. With the help of my wife Jackie, my two sons William and Daniel, and their good friend Brandon, I was able to keep the firebox stoked the needed twelve hours. Even with the wind blowing and temps outside dropping into the upper 20s F they helped me with little complaint. Thanks to all of them for the hard work.

I realy like the salt glaze effect on this candlestick holder. Grey green maybe from the bottle glass dust mixed in with the local Flora clay I am using on these.

My chimney flame arrestor had been working great! No more visits from concerned neighbors or the local police over flames shooting out in full view. lol

I enjoyed using my newly purchased pyrometer off Ebay. I still need to discover the correct location in the chamber to place the thermocoule probe. I was getting readings from it far below the actual temps I knew I was reaching. I must of had it in a cold spot out of the main flow of heat. Better luck next time.

Tiles and bricks came out great! Only lost two tiles to cracks. the white brick and pots are from the streambed creek clay. The low iron content make salt glaze not work well at the temps I can reach. I had much better flow this time thru the chamber for the gases. I found that stacking the bricks longwise to the exit flue with 3/4 inch gaps works good. Much less smoke in the barn this time! I will try to post some more pics of what came out soon.

Getting ready for the next firing.

Some of the terracotta tiles I have ready for the kiln firing coming up on my christmas break.

Ive made a new brick frog in honor of the town my latest kiln is located in. Notice the corndog clay insulated thermocouples ive made on the bench.

A few sample Flora bricks drying out ontop of the stove barrel in the barn.

Salt glazed bricks?

Here are a few photos of bricks I fired in the new kiln here in Flora.

All of them came out good and hard. I was also trying out salt glazing just to see what would happen on the bricks.

All of the ones on the bottom two layers showed the effects of the salt.

The heat must have been more intense the nearer they were to the firebox vents.

I will need to work on how I place them as they tend to sag and crack as they get that hot.

If I can perfect this they would make a very interesting and weatherproof outdoor bbq grill.

Second firing of the new Flora kiln. Much better.

Changes have been made and the results show much promise! With the help of the forced air blower, taller chimney, and 15 hour firing, my sons and I have hit the temperatures we needed. With this kiln I have learned to be more patient. It is bigger and wakes up slowly, like an old bear from hibernation.

I made some more bricks and a few pots to go along with the refires from last times attempt. The chamber is much fuller than last time . I still am working on the proper placement of everything to get good flow to the flue. Guess it will just take time to learn about this beast!

Some of my young help.

Smoke from the chimney was not to overpowering. Thats a good thing being at the edge of the town where people have to breath all of it if the winds shift to out of the west.

Early on I stoke the firebox alternating left side then right side. This keeps the cold flue and chimney from "choking" on too much gases. As it warms up I begine to stoke both sides together. I can only feed it everything it wants toward the end if the firing. Then its hard to keep up with its hunger.

Its at this point I begin the salt glazing. Nothing fancy, just throwing in a cupfull to each side of the firebox every other stoking. Im not sure how it will glaze though, the pots at the top may not be quite hot enough or not get the full effect of the salt vapors. We will see.

I will post to show the results after the cooldown.

Heres a short video of it for all of you.

Trial kiln run needs some improvement.

I fired my latest kiln up last saturday on a test run to work out any bugs it may have. There was alot of it that needed improvement! This is my first arched chamber and the location of the exit flue is low. This makes for weak draft until the chimney warms up. It smoked like crazy the first hour or so. Even after that it didnt draw like I wanted until after a few hours stoking.

Since I built this kiln at my new site, I had to bring over everything from the other location I was working at before. I hadnt bothered to bring the blower for the firebox. Wasnt sure I would need it. I think I do. Couldnt get it up past red. I couldnt reach the temperatures needed without it in my short firing timeframe. 1 day. So that little blower is gonna be a must have for this kiln too.

I built the upper part of the chimney in a hurry the days before the first firing. I didnt like its look or the gaps in the brickwork. Neither did the local policeman on duty. lol. That night he payed me a visit worried that the flames he saw shooting up from it were gonna burn down the barn. Guess he wasnt used to seeing chimneys shooting out flames after wood stoking. I have since rebuilt it taking the time to do it right and make it a couple feet taller for better draft.

Ive found a new sorce of field clay I am excited about that it seems to work much better. I will post when I have some results for all of you to see.

My first brick kilns video

Here is a short video record of my brick and pottery kilns.