A question about air inlet/exhaust port on a Kilncare Ikon kiln

[Smorzando]

Hi folks,

I recently bought my first kiln - it is a Kilncare Ikon V46 toploader (I’m in the UK). It is a 13amp plug in kiln, fairly similar in design to the small Rohde and Nabertherm kilns.

It has a small air inlet port on the lower right hand side and an adjustable exhaust port on the upper left side of the chamber. There are no peepholes.

I’ve done two bisque firings in the kiln during which I closed both the inlet and exhaust at 600 degrees C. However I am about to do my first glaze firing and am utterly confused as to what I should do during this type of firing regarding when (or if!) to close the inlet and/or exhaust. 

The manual simply says ‘For glaze vapour, the vents will be closed after the glaze has finished releasing’.

Um…what?? I have spent the last six hours or so driving myself nuts trying to read the entire internet to get an idea of what I should be doing in terms of ventilation during a glaze firing. Since the Kilncare Ikon is not a very widely known kiln, I’ve been trying to get an idea of what people do in Rohde or Nabertherm kilns with similar designs, but am still at a total loss. 

If anyone could give me some advice I’d be extremely grateful! Thank you.

[Min]

I'm not familiar with your kiln, does it have a vent? Could you post a picture of the "air inlet port" and the "adjustable exhaust port"? Sounds like these might be functioning  as what we on the other side of the pond use spy/peep holes for? (apart from using to see cones)

People have different opinions on when an electric kiln glaze firing should be closed up during the firing. For my kiln (without a vent) I close the peep/spy holes up at around 750C. 

Congrats on your new kiln!

Edited July 22, 2023 by Min
clarity

[Smorzando]

Hi Min

Thanks very much! I was actually mid way through the firing when I got your reply.  I decided to close the vents at 600 C - I asked someone with a Rohde kiln (with a similar arrangement of vents) and that’s what he said he does. Helpful to know you also close your kiln up at 750. 

I don’t know why the European kilns have this set up and don’t seem to have peepholes, but there you are .

I have attached a couple of photos to try and give an idea of how it looks.

 

[Bill Kielb]

Many of these kilns use the buoyant properties of hot air to remove fumes instead of a mechanical fan, often called stack effect. At the conclusion of a bisque firing it is generally assumed all significant off gassing has occurred. Bisque firings work because of peak temperature and sufficient time in the firing for all this to occur. Even glaze firings have glazes which contain clay, and oxides  which need to off gas almost as if being initially bisque fired.

So suction is determined by the diameter of the pipe, final height of the vent termination above the kiln and the temperature difference of the air. Height being a very significant factor. So in general, at bisque temperatures most off gassing is done, so that sets a credible termination temperature and depending on the height of the installation the inlet and discharge ratio is set to maintain a very small amount of air through the kiln up the outlet pipe …… just enough to prevent fumes from infiltrating into the kiln room.

opening the discharge a bit more than the inlet will ensure the kiln stays negative with respect to the kiln room. How much required is often a very very small amount and very dependent on final height. Open too much or too long wastes energy and in the extreme case could affect how even the kiln fires. So trial and error often establishes this.

A reasonable way folks often figure this out is the smell of wax resist burnout. If one can smell the wax early on in the firing, the kiln atmosphere is leaking into the kiln room. So opening the vent (s) just enough or slightly more to ensure this smell is exhausted …. and establishing this ratio (of discharge opening to inlet) results in a reasonable expectation that all fumes are being removed. Closing these after bisque temperature reasonably ensures a minimal amount of energy is wasted. The challenge is often to get inlet and discharge ratio established during bisque and then close the inlet only after bisque temperature so any very minor leakage will be out of the kiln room. The stack effect will always try and pull air out of the kiln.

Sorry for the complexity, but logic often says bisque temperatures are the magic number. Most manufactures stress the kiln must be vented but the variability makes it hard for them to provide uniform settings for all.

Edited July 23, 2023 by Bill Kielb

[Smorzando]

Thanks for your reply Bill.

I’m afraid it’s left me even more confused to be honest! I am working myself up into a bit of an anxious state about all this. Having never fired a kiln before it is all rather daunting and reading so much online where most advice seems to conflict, leaves me feeling like I am getting everything wrong and will damage the kiln, the pots, etc etc! Here’s the only info from the instruction manual regarding the vents:

The vents

Your IKON has an inlet port, on the lower right hand side of the chamber and an exhaust port on the upper left side of the chamber.

The inlet port can be opened or closed by sliding the shutter arm forward or backwards.

The outlet port has a shutter flap that is opened or closed using the black ball handle on the outlet exhaust. Move the Handle in towards the kiln to close the kiln and away from the kiln to open it. The handle can be left anywhere In between to limit the amount of air leaving the kiln.

For a biscuit firing the exhaust port should be left fully open up to a temperature of around 600c in order to allow all moisture from the work to be released from the kiln chamber. The inlet port can also be open if there is plenty of moisture to be released from the ware during this cycle if not required.

After the drying temperature has been reached the vents would then be closed to allow the kiln to reach its final temperature.

For glaze vapour, the vents will be closed after the glaze has finished releasing.

For cooling the vents can be opened at any point after the final temperature has been reached. At this point it may be of advantage to open both the inlet and outlet ports. However, when and how the vents are opened for cooling is very much a preference.

 

I should point out maybe that the kiln is in a wooden shed (with a concrete floor), it is rather draughty in there and there is a small window always open. But there is no other specific ventilation. 

 

[Bill Kielb]

53 minutes ago, Smorzando said:

I’m afraid it’s left me even more confused to be honest! I am working myself up into a bit of an anxious state about all this. Having never fired a kiln before it is all rather daunting and reading so much online where most advice seems to conflict,

Yes, lots of interesting advice. The basis for venting with respect to fumes is what I tried to convey. If I had one wish looking back, it would be that I wish I learned the underlying why parts first instead of looking for a magic number, temperature etc…. Very confusing I know. It’s a fun journey, no matter the path.

[Hulk]

My guesses are:
a) the port wide open during early bisque, then open enough throughout such that there's a small stream of outside air displacing kiln atmosphere, and
b) about the same for glaze fire - open early, allow a small stream throughout, but maybe close when the kiln is shut off, if it is cooling too quickly, or there's a cool spot due to air flow.

My kiln was fitted with a fan powered downdraft exhaust.
The fan system pulled a small stream of kiln atmosphere through small holes (two .25 inch holes, if I remember)* in the bottom of the kiln.

I ran the fan throughout bisque fire, on the way up and on the way down (burnout could still be happening on the ramp down from peak, yes?).

For glaze fire, I ran the fan throughout the climb to peak, drop and hold, and controlled cool, turning off when the elements are turned off.
I plan to do the same with my new kiln.

The make-up air, some came through a small hole drilled in the lid, and to be honest, mostly through spaces here and there between bricks and such.

The idea (mostly from reading, also talking with potters) being the outside air helps
  i) burn out stuff in the clay
  ii) the elements last longer
  iii) brighten glazes
  iv) remove some of the fumes from the area

Note the word "some" - there were still fumes, just not as bad.
 

*Per Bill's suggestion, I could tell the fan system was working, as the wax burnoff smell was plenty strong downwind from the fan exhaust (outside).
Also, the fan exhaust was clearly warm due to the tiny stream of superheated air, even when mixed with mostly ambient!

[Min]

18 hours ago, Smorzando said:

I’m afraid it’s left me even more confused to be honest!

Complexity bias is definitely a real thing but it's hard to avoid sometimes!

If I had your kiln I would leave both the bottom air inlet plus the exhaust port open during a glaze fire until you get a bit hotter than you did at 600C, If your glazes turn out wonderful with shutting the inlet and exhaust port shut at 600C then great but  what you are trying to avoid is deterioration of the elements due to gases/fumes from the glazes attacking the elements so they last longer. 

Are you okay on how you bisque fired? What type of clay are you using and what was your bisque procedure?

Edited July 24, 2023 by Min
clarity

[Bill Kielb]

Just a late add - Nabertherm does a nice job IMO of explaining a bit about the fresh air and exhaust port. In addition, they suggest when to open and at what temperature to close.

Manual https://nabertherm.com/sites/default/files/noindex/2023-07/M01.1089_English_2023-06.pdf

• Section 5.5.6 - section about how the vent works with reference to piping, slope and height.
• Section 5.7 - first firing with fresh open 100% of the time to 950 c to season the elements and burnout in a new kiln. Just a good thing to know for future use.
• 6.5.1.1 - some nice preset program firing charts with reference of suggestions of when to close the fresh air inlet. Their range 950c-1250 c depending on type of firing, 

Anyway, it may seem confusing but this does give reference to a  suggested temperature to close the fresh air vent, and these appear to be me to be relatively conservative numbers.

This may help a bit. Perhaps confusing now, but likely will have greater meaning as you fire more and more and gain greater knowledge.

sample schedule below with specific closure temperatures.

Finally - why are we doing this? Here is a nice article from this web site that could give you an idea of what we are burning out and about when this happens. https://ceramicartsnetwork.org/ceramics-monthly/ceramics-monthly-article/Bisque-Firing-101#

Edited July 24, 2023 by Bill Kielb

[Smorzando]

14 hours ago, Min said:

Complexity bias is definitely a real thing but it's hard to avoid sometimes!

If I had your kiln I would leave both the bottom air inlet plus the exhaust port open during a glaze fire until you get a bit hotter than you did at 600C, If your glazes turn out wonderful with shutting the inlet and exhaust port shut at 600C then great but  what you are trying to avoid is deterioration of the elements due to gases/fumes from the glazes attacking the elements so they last longer. 

Are you okay on how you bisque fired? What type of clay are you using and what was your bisque procedure?

Hi Min, gosh - complexity bias! I didn’t know this was a ‘thing’. Describes me to a T! 

To demonstrate this, I actually had about seven different clays in the firing together with a whole bunch of new glazes I’d made (as I said, I’ve never made a glaze before, or indeed done a glaze firing in a kiln!) - surprisingly, in fact amazingly, I have got some really nice results - lots to work with going forward, and I think one of the lessons I’m taking away is that I need to simplify things for a while til I gain more confidence

 

[Smorzando]

3 hours ago, Bill Kielb said:

Just a late add - Nabertherm does a nice job IMO of explaining a bit about the fresh air and exhaust port. In addition, they suggest when to open and at what temperature to close.

Thanks Bill. This is really helpful. As well as getting me to understand ‘why’ things are done - and why there are no hard and fast rules when it comes to ceramics! 

I certainly have lots of learning through experience to do - so I will take all this on board but also attempt not to get too tangled up in overthinking. As I said above, the glaze firing I just did was remarkably successful and I have some nice test pieces to use as ideas as where to go next. 

[oldlady]

to simplify even more,  use a mirror or clear flat glass to determine the amount of moisture still in the kiln.  whatever degree of temperature you guess at, the glass tells moisture level accurately no matter how heavy or closely packed your kiln is each time.  each firing is different so temp reading alone is not as accurate.

hold a clean glass horizontally above the top opening.   if the glass steams up, wait for awhile and try it again.  my kiln is clear at about 1000 degrees F.  do not know C.

do wear a glove or use a potholder so you do not lead the heat to your fingers and burn them.  my glass is from the dollar tree and is in a metal picture frame so it is big.

 

Edited August 10, 2023 by oldlady
add

[Bill Kielb]

Good trick to know for sure with the mirror for moisture!  Bisque firing is also about Sulphur compounds which begin around 600 c and can be corrosive to elements and humans. Also some late off gassers above about 800c. Your mirror may clear before this. So when in doubt, closing the vent later would be a conservative way to try and ensure all the bad stuff is eliminated. As you might have noticed, the earliest Nabertherm suggests is 950c to be conservative I believe.

Edited August 11, 2023 by Bill Kielb