Jump to content

Seeking advice on reduction firing with Gas Kiln


Recommended Posts

I have an Olympic torchbearer 18" top draft  gas kiln and haven't payed much attention to reduction or oxidation until now but I am interested in doing some things with reduction and I was wondering how this hobbyist can tell if I have a reduction atmosphere or not. I usually adjust it to get a clean burn below and have virtually no flames out the top. I am wondering if that means I have an oxidation atmosphere in the kiln and what I can do to make it a reduction atmosphere. I have a set of bricks I stack on top to protect my garage from the affect of the kiln and I pre-position a brick so I can seal the kiln for cooling. I notice if I push in my sealing brick to partially cover the hole, flames start shooting out of the hole of the kiln into the brick chimney. Is this causing a reduction atmosphere? I don't have money to buy an O2 sensor so hoping I can determine it without one. Thanks. 

P.S. I cant really see my cones through these tiny peep holes. Any advice on how to make them easier to see? 

Kiln1.jpg

Edited by kraythe
Link to post
Share on other sites

I use a home made propane downdraft kiln and the way I tell if it's in reduction is when there's a 6 inch flame shooting out of the chimney.  Less flame = less reduction, more flame = heavy reduction.  I like the way the 6 inch flame turns out so I keep it there.  It's actually pretty difficult for me to get to temperature without at least a little reduction.

 

And yes restricting the chimney (damper) you can put it into reduction.  Also I use cones as more of a witness because I have no peep holes, I mostly go off of my pyrometer.

Edited by liambesaw
Link to post
Share on other sites

Burn the clean with clean flame until 1800 degrees-then push in the damper over the flue Exit until a flame comes out as noted in above post.

when its reducing its not a clean but a dirty atmosphere . Flames will come out your spy plugs. This is when you need a digital pyrometer to see if kiln is stalled out or climbing . They are pretty cheap so get one if you plan on doing this as well as a protection type for actually thermocouple.

Keep the kiln is reduction while  it climbs to whoever temp you are going to.

Use a kiln shelve cut to make a sliding damper over hole . It can be between the bricks you have there.

Moving those bricks is a pain  compared to a damper

Link to post
Share on other sites

I have a pyrometer but it doesn't do as good of a job as cones because cones measure heat work and pyrometer just instant temp and I don't have them on all levels, just on the middle ring. So I can do the flames trick because I want to do some cool stuff with temoku. I have been firing cone 10 and finding out my cones are not down all the way so things are being underfired and its frustrating to not know just how much work is being done. 

Link to post
Share on other sites

You need both cones and a pyro-the cones tell you when the fire is done (end point). The pyro tells you that the kiln is still climbing when in reduction and that its not stalled out (not climbing)

In Gas firing you use both cones and a pyrometer. 

Again fire until 1800 degrees burring clean then push in the damper until flames come out (this is when your digital pyrometer ) will tell you the fire is slowed down but still climbing .

Keep some reduction until the cones are end point and fire is over-close damper .

Link to post
Share on other sites

Get the welding googles-do a search from main page on this as its be covered to death here.

Spotting cones in any hole is a skill.

You need a backdrop brick and the right dark wielding glass-(some like a laser light)-I have never used one.

In small holes only one or two cones can be viewed .-Just make sure the chunk of soft brick or a clay slab sits behind to give you a visual wall to view the cones.

again this is a skill and the right safety glass-you will use both.

 

I searched the main page and there are many threads on reading cones

here is one

 

Edited by Mark C.
Link to post
Share on other sites

No have too have the right glasses to view cones without hurting your eyes. The rays are bad for you. Get the welding glasss that is suggested in many threads-set the cones in front of a solid surface check it out when you are loading to make sure its visible . Its all part of the learning curve.

Many biginners struggle with this so just work thru it.Get a laser pointer if you want-You have to see the cone that matters in terms of end point shut down.If you cannot do this drill a larger spy plug hole in center of kiln and make a larger soft brick plug to plug hole.

Link to post
Share on other sites
  • 1 month later...

With respect to seeing the cones in a heavy reducing atmosphere we have begun using a cheap Green laser that can be focused to a dot or enlarged to a spot. In spot mode the laser illuminates the cones perfectly. In dot mode it is almost too bright and difficult to aim steadily without getting an annoying reflection. With respect to reduction there are some simple things that you can do to establish if you are in reduction during your early firing to give you a better idea of how your burners respond and of course the spyholes showing a proper reduction flame will be a reasonable indication that you are in reduction, top to bottom. We have started to make videos on these topics for the greater art community and sharing them on our you tube channel at Madison Pottery. An O2 meter is best if you can afford, but this can be done by sight and recording temperature rise early on for how much air they need to fire in oxidation then working from there. In the next month or so we will likely be able to put up a decent video  illustrating more clearly how to do this. 

Edited by Bill Kielb
Link to post
Share on other sites
  • 4 weeks later...

little kilns are IMO much more difficult to maintain atmospheres than a bigger kiln. The small nuances in primary and secondary air make huge impacts in the atmosphere.  a 1/4" closed on your damper might eqaute a 2" on my bigger 60 cubic foot kiln. An O2 sensor would allow you to visually understand what is happening when you make small tweaks to your setup, but without one you're going to have to rely on learning the flames and what that means to your glazes and desired results. You may end up finding out that reduction is great for some glazes and not for others; when I was a noob I thought if it wasnt reduced then it wasnt worth it (big flames are coooooolll!). Most of my work is now cone 12 ox, except for my cone 10 copper reds.

  If you've never learned/experienced reduction before, reduction is gained by eliminating/reducing the amount of O2 in your kilns atmosphere. This is done via two different methods, or combinations of them; increasing fuel source to air ratio, increasing air source to fuel source. Fuel source is controlled only one way; either add it in, or back it out. Air is controlled by your burner, burner set up, or damper. Primary air comes in through your venturi burner tube; you can adjust this with the rotating dial on the back of your burner. Secondary air is just as important as your primary air; secondary air comes in from any other source (mainly burner ports) of air in your kiln's exterior; secondary air is mainly controlled by the damper. Close the damper down, there is less draw in the kiln, less secondary air getting sucked in, consequently less heat, but also less Oxygen=reduction. Open it up, there is more air coming in, more heat, and less reduction. Your burner tip should be about 1" at least away from the burner port itself; this allows adequate secondary air to enter. You can also increase the amount of secondary air by having your burner ports being a "funnel shape"; on a 4.5" or 9" wall this is done by cutting the bricks around the burner port to have a bevel angling into the kiln. On a 2" brick I would not advise cutting the brick away. If your kiln stalls I would suggest fiddling with the damper before messing with your air/fuel controls. More fuel does not mean more heat. After I enter reduction at cone 012-08 (depending on glazes) I dont mess with my primary air, only fuel amounts and damper settings.

   Finding the right amount of reduction, how long of  a reduction, and what glazes like it will take a while. The small kilns allow you to fire more regularly, but IMO they are harder to learn on because little changes make a big impact, so keep accurate notes and have ways to measure your actions (small notches drawn on your kiln lid to measure damper adjustment, turns of the dials, etc).

As far as seeing your cones; all the above suggestions are great; a reduced atmosphere is often times even harder to see your cones in. If possible I like to place contrasting objects behind my cones; same principle as in a electric kiln when your cone pack is placed in a line of sight, but in front of an element channel (provides contrasting colors in the heat). In a gas kiln I like to place objects which dont offer a completely same surface behind my cones. I also blow on them sometimes when I cant see them clearly; be careful doing this...many a beards/eyebrows/hair lost to practices like this. A quick puff of air cools the cones down momentarily, but to get close enough to do so is a hot zone. Cones also need to be near the spy hole for this to work. Welding goggles and practice. Good Luck!

 

Link to post
Share on other sites

With an updraft like you have (and I have), in my experience,  you're going to get flames coming out of the flue hole at some point in the firing to get it to target temp.

There's always going to be some reduction in the atmosphere. However some flame is okay, it's when fuel is not being burned and you see smoke that it's in heavy reduction.

You need to monitor that flame to where you're not getting smoke.

On the stacking 'protection' bricks on top, try instead making a 'chimney' (4 sides) using the same bricks next time. I'll use 3,4,5 hard bricks stacked on their sides or ends. This will help draw the air up through the kiln.

I'll use a a piece of 1/2" kiln shelf as a flue to adjust the flame and reduction. My kiln is super sensitive to this. Just a 1/4" move i the flue makes a difference.

You have to be delicate in moving it as there can be brick crumbs that will fall onto your ware through the flue hole though.

 

One way, bricks standing on end...

IMG_4460-XL.jpg

Link to post
Share on other sites
  • 1 year later...
On 12/13/2018 at 2:12 PM, Rex Johnson said:

With an updraft like you have (and I have), in my experience,  you're going to get flames coming out of the flue hole at some point in the firing to get it to target temp.

There's always going to be some reduction in the atmosphere. However some flame is okay, it's when fuel is not being burned and you see smoke that it's in heavy reduction.

You need to monitor that flame to where you're not getting smoke.

On the stacking 'protection' bricks on top, try instead making a 'chimney' (4 sides) using the same bricks next time. I'll use 3,4,5 hard bricks stacked on their sides or ends. This will help draw the air up through the kiln.

I'll use a a piece of 1/2" kiln shelf as a flue to adjust the flame and reduction. My kiln is super sensitive to this. Just a 1/4" move i the flue makes a difference.

You have to be delicate in moving it as there can be brick crumbs that will fall onto your ware through the flue hole though.

 

One way, bricks standing on end...

IMG_4460-XL.jpg

 

Hi Rex: I have a Torchbearer and have tried to use a chimeny similar as yours but have noticed that it slows down temp increase.  I took it off.  Then I wondered if maybe you put it on later on maybe when reduction begins?.  Or you leave it on top since the beginning?

Thank you all for your inputs.  Happy firings.

Link to post
Share on other sites
17 minutes ago, TallerJMC said:

 

Hi Rex: I have a Torchbearer and have tried to use a chimeny similar as yours but have noticed that it slows down temp increase.  I took it off.  Then I wondered if maybe you put it on later on maybe when reduction begins?.  Or you leave it on top since the beginning?

Thank you all for your inputs.  Happy firings.

That post above is from December of 2018. You might want to pm him.

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.