Pottery/DK820X-2 Duncan Kiln Firing/Venting Questions
QUESTION: Good day Ti,
Let me begin by thanking you for guiding me through my first official small firing using the information you gave to a past questioner AnneMarie (regarding her Older Duncan DK1020-2 kiln) I recently purchased an older Duncan myself, the Kiln I bought had never been used. It is a DK820X-2. Before doing this firing, I first did an empty Cone05 firing using the information given in a substitute manual I found on the Internet from Paragon kilns. It ran for 6 hours, and the kiln sitter did not shut off, nor did the kiln sitter cone bend. Being a beginner potter myself, I blame myself for interrupting the firing but I was nervous about the whole process, and turned the kiln off. Looking for additional information, I came upon this website, and your answers to AnneMarie. I realize now, I should have turned both dials on, not just the bottom one. Well, todays firing went beautifully, the kiln turned off by itself, and both cones bent. (kiln sitter and self supporting) the entire firing from start to finish was in a little over 5hours total. I monitored the temperature with a pyrometer I had from a small glass kiln I own. I increased the firing every 800*. low for 2hrs, med for a little over 2hrs. and high for just a little over an hour. The few pieces I fired came out perfect, it was a bisque firing.
My question is, do you ever hold ceramic bisque or glaze firing at one temp. as I do in glass firing? And for what reason if you do? Also, how would you do this with this type of kiln? (using the med/hi dials?) and at what temp would you hold it at? The reason I am asking is because some articles I read, it mentions holding. So, I am a little confused. Also, on the dial, it has Hi Fire as well as just Hi/med/low. Why would if ever, do you use the Hi Fire setting? Again, thank you again for today, your advise to AnneMarie gave me the confidence I needed for a successful firing today, and thankyou in advance for answers to my few questions. Though I love glass fusing, I am really falling for the wheel, and hand building pottery.
ANSWER: Dear Barbara,
Thank you for your recent comments and questions. It is nice to know that potters look for answers before asking. I am very glad that you were able to fire up your kiln using the instructions given to AnneMarie.
As for your firing, as long as you place the appropriate cone in the cone sitter, your kiln will fire a glaze firing just as it did your bisque. What you should know is that you want to place a cone pack inside your kiln in the middle of the shelf where you can see it from the peep hole. A cone pack is a set of cones in the following order. One cone lower than the maturing cone, the maturing cone and one cone higher.
The purpose for the cone pack is to be able to see where your kiln is in firing. Let's say you are doing a cone 5 glaze firing. You would use cone 4, cone 5 and cone 6 in that order. On your first glaze firing, you will need to watch the kiln during the 4th hour by looking into the peep hole, using welding glasses, and checking cone 4. When it starts to bend, you have approximately 15 minutes before it bends completely and cone 5 begins to bend. The same for cone 5. Once cone 5 bends or matures, the kiln sitter should shut the kiln off as the cone 5 cone will bend in the sitter to match the cone 5 cone in the kiln. In a perfect firing, cone 6 will have started to bend.
If you look at a cone chart, you will see what temperature the cones reached.
Holding is primarily used when firing crystal glazes. The hold is done so that the crystals mature. There are other reasons to hold a kiln, but if you are just starting out firing glazes, you will probably stick to standard glazes and not have to worry about holding until you decide to work with alternative glazes, such as crystallines.
However, if you choose to use a holding pattern for the crystalline glazes, you will need a pyrometer to be able to tell where the kiln temperature is at. Normally, the kiln is turned down by using the l/m/h knobs. Then the kiln cools to a specific temperature and is allowed to set at that temperature for a set amount of time. Usually between 15 and 30 minutes. Then the kiln is brought down completely.
The Hi Fire setting is just that, a high fire firing. If you are using porcelain, this is the setting you will want when firing glazed pieces. If you are bisque firing, firing as you did your bisque firing earlier. Of course, if you are firing stoneware, earthenware or terra cotta, you will only use the l/m/h settings.
I hope this answers your questions. If you have further questions, please feel free to contact me again anytime. I am always at your service.
Ms. Ti Phillips
Earth Stoke 'N Fire Pottery Studio and Artist Retreat
---------- FOLLOW-UP ----------
QUESTION: Thank you Ti, I appreciate your speedy advise.
Another question, what are your views on venting out? Some say it is important to do so only for glazing. My kiln is in my garage. A woman I know who does kiln repair said she felt as long as I have a door open and/or the top peep hole open during the firing that should be enough. She feels that because todays glazes and clays are non toxic it is okay not to vent out underneath the kiln, or have the overhead vent as suggested in the past. Maybe her answer would be different if my kiln was in an enclosed area in a building. What do you think?
Thank you for your comment and recent follow up question. Venting is as important as protecting yourself from clay dust and glaze dust. Your friend is very misinformed. Not all glazes and clays are non toxic. In fact many contain raw materials that are toxic during the first few hours of firing.
The reason I can attest to this is I am a clay and glaze chemist and have worked with these materials in their raw state for over 25 years. I teach clay and glaze chemistry for students who wish to develop their own clay and glazes. I have written over 85 pottery classes which I currently teach online and here at my retreat.
Since you are not making your own clay and glazes, but rather purchasing manufactured products, the raw materials to make these products are not available to you to identify the contents. Therefore, precautions should be taken to avoid unnecessary exposure.
Think of it this way. If you were near a home that was burning, you would definitely not stand in the path of the smoke because of the different chemicals that would be filtering into the air. A kiln does not put of smoke if in an oxidation atmosphere, however, I can guarantee there are raw materials expelling from the kiln and how these raw materials mix is what gives you toxic fumes.
I feel bad when someone gives information such as this to a novice potter, especially without doing some research on the subject and just assuming. Fortunately, you do try to research and have come to the right place for answers. You are welcome to show your friend this post and hopefully enlighten her on the firing process and fumes. I would be glad to answer any questions she may have also.
In your case, leave your garage door open during firing. If you have a side door, place a box fan at the door facing out so the fumes are drawn out of the garage. Wear a mask anytime you are near the firing kiln for protection. Leave the peep hole cone in to prevent excess fumes from escaping the kiln.
If you have further questions, you are welcome to contact me anytime. I am always at your service.
Ms. Ti Phillips
Earth Stoke 'N Fire Pottery Studio and Artist Retreat