Firing

[LisaJJ]

Hello, I'm new to this forum after taking up Ceramics after a long break. I've just bought  new kiln, Potclays Silver Toploader electric kiln, and up doing the 1st test firing to check its working properly etc. Question, do I leave the 3 bungs and spy hole bung in or out? My manual says to put in the spy hole bungs after about 4 hours, but I'm not sure if this is referring to the spy hole on the lid or the 3 bung holes going down the side? There's no diagram with manual and am guessing. I would call Potclays but its Saturday evening and I've just fired it up. Many thanks in advance. Lisa

[oldlady]

eliminated my post, did not read the question carefully enough.

[Min]

3 hours ago, LisaJJ said:

I've just bought  new kiln, Potclays Silver Toploader electric kiln, and up doing the 1st test firing to check its working properly etc.

If it's a brand new kiln with new elements the first firing should be a slow bisque firing with the kiln empty and all the spyhole covers out (if there is no vent on it) to whatever cone or temperature the manufacturer recommends. You want any moisture, machining oils etc to be vented plus for the elements to oxidize to build up a protective layer.

[Bill Kielb]

3 hours ago, LisaJJ said:

Question, do I leave the 3 bungs and spy hole bung in or out? My manual says to put in the spy hole bungs after about 4 hours,

If it’s a new kiln and especially if an empty test fire, you might want to load your furniture just to get some thermal load p. Then run your normal bisque to cone 04 (1063c).  Normally leaving a few bungs out for four hours is plenty of time to remove moisture and get plenty of oxygen. I wouldn’t take the top one out, just wastes energy really. So to season the elements and remove any dust / oils etc….. a slow bisque to 04 with the bungs removed for four hours likely is just fine. Now, what’s a slow bisque to 04?

Just a suggestion, the Stanford control that usually comes with these is a segment control and Stanford is big on ending with a soak. My suggestion:  read up on cone firing, use witness cones, they are made of glaze and will accurately represent how much heatwork was done on the glaze and clay. Firing to a top temperature is really not an accurate way to fire ceramics. What is important though is the speed with which something is fired especially during various phases of the firing.

I would suggest to get witness cones, a cone firing chart, learn cone firing and create a slow bisque and slow glaze firing schedule to match your clay and glaze to save yourself a bunch of learning time.

Here is an article about seasoning elements https://skutt.com/images/Top-5-ways-to-Extend-the-Life-of-your-Kiln-Elements.pdf

Bisque firing article https://ceramicartsnetwork.org/daily/firing-techniques/electric-kiln-firing/bisque-firing-schedule-help-prevent-glaze-faults/

Are some sample schedules with approx. C conversions https://ips-cic-filestore.s3.amazonaws.com/r278179/monthly_2021_03/B7AD028E-B25D-40BC-8595-DD42F34FF1E4.jpeg.a770dc28387aa0f09a51eb651ba5672e.jpeg?X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Content-Sha256=UNSIGNED-PAYLOAD&X-Amz-Credential=AKIAJZ2HKAZ3HINDYD7Q/20210731/us-east-1/s3/aws4_request&X-Amz-Date=20210731T235206Z&X-Amz-Expires=1200&X-Amz-SignedHeaders=host&response-content-disposition=attachment; filename*=UTF-8''B7AD028E-B25D-40BC-8595-DD42F34FF1E4.jpeg&response-content-type=image/jpeg;charset=UTF-8&X-Amz-Signature=e76a9a0ab1051174fdb0e41baebb87f340c36c3f25ff3a517fae518f4476ab46

 

 

 

[Min]

@LisaJJ, are you firing to earthenware or stoneware temps?

One other snippet about conditioning elements, this one from Euclids which is a company that supplies kiln elements to many manufacturers. With all due respect to Bill I disagree about only needing to keep the spyhole plugs out for the first four hours.

"Why and how should I pre-oxidize my elements?

Pre-oxidizing the elements is recommended for customers using their kilns at elevated temperatures (cone 6 and higher), or under corrosive or reducing conditions. To oxidize the elements, heat your empty kiln to a temperature above 1922F/1050C with the peep holes open and the lid raised slightly. Holding the temperature there for 6-8 hours will ensure thorough oxidation of the elements, but most of the oxide growth occurs in the first 1-2 hours. This procedure grows a protective oxide coating on the elements before the elements are exposed to any harmful atmospheric conditions. This procedure is usually only done once, but can be repeated as required if the kiln is fired under harsh conditions such as a reducing atmosphere (which actually removes the protective coating)."

And from the link from Skutt that Bill provided:

"4. Vent! Vent! Vent! Even if you have the best oxide coating ever, the fumes that emit from clay and glazes can still attack the element when it expands through heating and forms cracks in the coating. Downdraft vents are your best defense against potentially harmful fumes. Downdraft vents pull the fumes from the kiln chamber before they have a chance to damage the elements. If you do not have a downdraft vent your next best option is to prop the lid a couple of inches until the kiln reaches 1000 F to allow the fumes a path to flow out of the chamber. You should also leave the top peephole out during the entire firing to handle those fumes that escape above 1000 F."

[Bill Kielb]

3 hours ago, Min said:

One other snippet about conditioning elements, this one from Euclids which is a company that supplies kiln elements to many manufacturers. With all due respect to Bill I disagree about only needing to keep the spyhole plugs out for the first four hours.

I am good with either approach actually as long as one applies some technique. Most of the published techniques are similar actually. As far as all plugs all the time, if your kiln will make it, fine but an empty kiln has nothing but air in it really. If your kiln will make temp then Euclids method likely grows a thicker oxide layer. I am pretty happy if folks do something to grow some oxide. I am a pretty staunch advocate of not wasting a bunch of energy though for the sake of the electric bill or the sake of the planet. Long drawn out empty kiln firings with everything propped open waste energy.

The point is, do something within reason, longer is better but realize whatever layer you produce is not likely to get you 50 or 100 more firings, maybe 5, maybe 10, maybe 20 if you fire in reduction. Euclids mentions most of the layer grows in the first hour or two so at some point holding for six hours becomes excessive and all these techniques becomes equivalent. Remember, all these techniques  are in and of themselves a firing in your firing count so at some point does holding longer count as 1-1/2 firings? I have not seen published data on comparing oxide layer thickness and longevity actually.

 IMO: Do the Euclids technique if you have power, time and spare electric, but do not be surprised if your kiln struggles to make 1050 c with the lid propped and all the plugs out nor would I be surprised if the elements needed changing at 100-150 firings as usual. My point, In my opinion and experience, I am happy if you do something reasonable and consistent with the published material out there.

The vent @Min mentions is a good point for your normal firings. Not sure if this kiln comes with its own or needs an additional vent installed but vents have proven very useful and effective.

[LisaJJ]

18 hours ago, Min said:

If it's a brand new kiln with new elements the first firing should be a slow bisque firing with the kiln empty and all the spyhole covers out (if there is no vent on it) to whatever cone or temperature the manufacturer recommends. You want any moisture, machining oils etc to be vented plus for the elements to oxidize to build up a protective layer.

 

[LisaJJ]

Thankyou for your reply. I was recommended firing to 750, but mistakinly fired to 700, once kiln cooled I realised the cone hadn't gone over. Will repeat the firing to 1000, but will need to purchase cones first. I must say I really am not very experienced regarding cones etc. Completed my ceramic degree almost 20 years ago, and need a re fresh, (although I've made a heap of stuff ready to fire)

Can you recommend a specific chart regarding cones and firing temeratures? Thankyou, Lisa

[Bill Kielb]

@LisaJJ
Can you recommend a specific chart regarding cones and firing temeratures? Thankyou, Lisa

Her you go: https://ceramicscapes.com/wp-content/uploads/2017/03/cone_wall_chart_horiz.pdf

also cone position chart below others have found handy.

[Min]

@LisaJJ, when you look at the cone chart Bill linked to be sure and read the blurb on the right side and note that the speed of the firing makes a difference to the melt of the glaze/cone. For all firings the heat rate for the last 100C is important to note. If you are interested in more reading Orton has a wealth of info on their site. 

(nice to see someone here from Wales! My dad and little sister were born in Llanelli)

[LisaJJ]

13 hours ago, Bill Kielb said:

@LisaJJ
Can you recommend a specific chart regarding cones and firing temeratures? Thankyou, Lisa

Her you go: https://ceramicscapes.com/wp-content/uploads/2017/03/cone_wall_chart_horiz.pdf

also cone position chart below others have found handy.

Hi Bill, thankyou so much for your help. I re fired yesterday and cone went over at 1000. I need to purchase a whole load of them ready for my firing. Exciting times ahead. (Not too many cracks hopefully;) Lisa.

[LisaJJ]

12 hours ago, Min said:

@LisaJJ, when you look at the cone chart Bill linked to be sure and read the blurb on the right side and note that the speed of the firing makes a difference to the melt of the glaze/cone. For all firings the heat rate for the last 100C is important to note. If you are interested in more reading Orton has a wealth of info on their site. 

(nice to see someone here from Wales! My dad and little sister were born in Llanelli)

Hi, thankyou for your very helpfull reply. I'm in South Wales, Llanelli isn't too far from me, a beautifull part of the world as Wales is. Lisa