Mudfish1

Copper red glaze test tiles is a good idea - I will mix up a batch and make sure I have some test tiles in my next firing. I fired a large West Coast gas kiln for many years, but when the studio closed I moved to my garage, switched to a Cone 8 electric kiln, and reformulated all my glazes to Cone 8. Now that I am moving back to Cone 10 gas firings, I will dust off my old glaze recipes and get used to my small gas mystery kiln. I had a copper red formula that was great because it was beautiful in reduction, but also a lovely green in oxidation. Hopefully I can blow the dust off my notebooks and find it! For anyone that has a small gas kiln, is it hard to get good reduction throughout such a small volume? Thx

Hi Neil; I always thought if you get a flame out the top, it meant that you had a reducing atmosphere in the kiln? Good idea on the clay color, when I do a real firing I will know how much reduction I got. I use a lovely iron-rich stoneware clay that gets nicely buff colored when it's reduced. Richard

Friends! I am happy to report a successful Cone 10+ firing in my mystery kiln! I have attached a picture of my cone packs at every level, with Cone 7, 8, 9, and 10 from left to right in each cone pack. Top of the kiln hit a hard Cone 10, and the bottom of the kiln just liquified all the cones. To fully liquify the Cone 10 like that, I am guessing I might have reached Cone 12+ on the bottom? Hard to be sure. First, using no damper, I fired the kiln up to about 2100 F by having my gas pressure as high as it would go with no standing flame from the vent. I wanted to see how hot I could get with an oxidizing atmosphere. If I avoided any standing flame from the vent, the kiln seemed to stall at around 2100 F. Then I slowly adjusted my gas pressure upwards and used the pyrometer to simply make sure that kiln temperature was increasing. I started to get a small standing flame from the vent, but I ignored it. I just watched the pyrometer. Every time the kiln stalled, I increased the gas just a bit. It was a painstaking process, but by making tiny adjustments to the gas pressure, I was able to hit a max temp of 2303 F based on my pyrometer. Less gas would make the temp start to drop. More gas would make the temp start to drop. So with no damper, I had found the optimal gas flow rate to maximize kiln temp. Note that at this point of maximum temp, I had a significant standing flame coming out of the vent (see picture). That means my kiln reached peak temp with enough gas flow to have significant reduction going on. This surprised me - I had assumed having extra unburned gas flowing through the kiln would cool things down, but the data was clear - I reached peak temp with a nice standing flame from the vent. I then did some experiments to test out the effect of a damper. Keeping the kiln stalled at that peak of 2303 F, I slid the damper on just a fraction of an inch. That made the temp drop. If I slid the damper on more, that just made the temp drop more. I took off the damper and got back to 2303 F, and then tried sliding on the damper while simultaneously decreasing gas pressure. I assumed I would be able to play with more damper/less gas and maintain the peak temp, but it didn't work that way. The damper made the temp drop. Deceasing the gas made the temp drop. I could not find a combination of more damper/less gas that reached my peak of 2303 F - every combination of conditions was cooler. So that part of controlling the kiln is still a mystery. I blew past Cone 10 with no damper and a significant reducing flame coming from the vent. Any use of a damper made the kiln cooler no matter what else I did. Given my results and what I described, I would appreciate thoughts on how to play with that damper/gas flow combination of factors. In the meantime, I can certainly get this little kiln to Cone 10 temp just by adjusting the gas flow! Thank you to everyone that's been reading my posts and giving me excellent ideas and suggestions on what to do.

Folks; Thanks for the continued interest and help during my quest for a Cone 10 firing! Mark it really helps to know that my burners are fixed (non adjustable) so that I can take that issue off my list of possible adjustments. I had read that some venturi burners are just designed to be efficient over a certain range of pressures, so it sounds like that is the case with my own little mystery kiln. Bill thanks for the nice illustrations of the burner flame and combustion tables. I will pay attention to the burner flame color as it enters the bottom of the kiln, that will give me a direct observation to indicate whether or not I have sufficient oxygen from the venturi effect, or if I am pushing unburned gas into the kiln. My understanding is that for any given damper setting, there should be a gas pressure that results in a good blue flame. More gas would then lead to excess fuel and a yellow flame? So is observing flame color at the burner a practical way to determine the max efficient gas flow into the kiln? David, I appreciate your artistic skills! I won't try to compete with my own drawing, but my shelves are evenly stacked with the first layer 3" above the kiln floor to create mixing box for incoming flames. Total interior height is about 27", so shelf spacing looks like (from bottom to top) 3" (from kiln bottom) 6" 6" 4" which leaves about 6" space to the bottom of the kiln lid. The idea of placing a last shelf a few inches from the lid makes sense - it would certainly reduce heat loss from that vent, good suggestion. In answer to the comments about my shelves, I am trying to keep it simple for now. I have > 1" space all around, and left a 1" gap in between shelves at each level. I didn't try to get fancy with staggered shelves, or with placing some shelves closer to the wall to block direct gas flow up the inner sides of the kiln. I've read about all kinds of creative shelf placement to block/channel/slow down the gas and force more mixing, but I wanted to master the basic kiln behavior before I got too creative with shelf placement. I remain intrigued with the idea of adding a short flue to get some buoyancy effects and increase the draw of air int the bottom. However, I am going to bet that the kiln was designed to make Cone 10, if I am smart about the gas pressure/damper combination. I have to believe that I can squeeze another 80-100 F temp increase out of the kiln if I play with the gas/damper settings, as everyone is suggesting! It may be friday before I get off work early enough to give this another shot. I want to start early enough that I won't be out there at midnight (again) trying to entice the kiln to get to 2300! Thanks everyone!

Folks! Thanks for the excellent feedback and help. Based on the suggestions, it sounds like my next step will be to fire again and play with the tradeoff between damper setting and gas pressure, and see if I can coax the kiln above 2300. David I didn't realize that a Type K thermocouple could be inaccurate above Cone 6, so I will definitely keep my witness cones in there during my next test fire. I am counting on the thermocouple to at least show if I am heating up or cooling down - as long as that works, I can play with it and use the witness cones to let me know if I am getting there. Bill, your comment about flame color was useful. The picture I attached was from early in the firing, at fairly low gas pressure. When I am towards the end of the firing and the burners are much higher, should I still see that nice blue flame? Does that blue color mean that there is enough air coming from the venturi burners? My understanding about venturi burners was that they were adjustable to allow more or less air to mix with the gas. I crawled under the kiln and removed the ceramic cylinder, and took pictures of just the burner and orifice assembly. The metal assembly you see in the side picture screws directly into a hole in the gas supply pipes under the kiln. You can unscrew it, but the whole assembly comes off - no moving parts. It's just a short metal can with a cross piece and disk with a hole that screws directly into the gas pipe. No moving parts. The second picture is looking down into that metal assembly. You can see the gas pipe at the very bottom, the short metal can rising up, a metal support structure going all the way across that's welded to the insides of the metal can, and then a small circular disk with the gas orifice itself. The little disk at the bottom also won't turn or move, and just seems to have a hole in it for the gas to come out. I don't see any way to increase or decrease the air flow - the bottom of the metal assembly is just open to the air, with that cross piece and small disk welded to the metal can, and the whole assembly just screws into the gas pipe below. Has anyone seen this burner design? Is it basically just fixed and not adjustable? Appreciate your ideas/comments!

Folks; Thank you for the excellent suggestions! Bill, it's a 3/4" line. I was worried about not having enough gas. I nursed it up to about 2200 F and never opened my valve more than 2/3 of the way (no pressure gauge, just a ball valve on the gas line). When I stalled at 2200 I decided to see how much I could still increase the gas flow rate - with the valve wide open I had about a 4 foot standing flame coming out of the kiln and started dropping the temp fast. I think that means I have plenty of gas flowing into the kiln, but as Russ was saying I don't have enough oxygen coming in from the venturi burners to get complete combustion, so all that extra gas doesn't burn and just cools things down. I haven't looked carefully at the burner orifices to see if there is a way to adjust airflow into the burner - should there be a twistable part or something that lets more air mix in? I'll have to crawl down there and take some pics and see if there is something I can adjust. Mark, I do have a shelf I use as a damper, but I wanted my first test firing to have the most air/gas flow possible through the kiln. When I used the damper to block about 1/4 of the opening, I got a higher exit flame and started losing temperature. I think I was reducing the oxygen flow into the kiln by restricting the exit vent, and getting more un-combusted gas out the top. As Bill said, I probably have significant heat loss through that large vent hole. If I can reduce the opening with a damper and then reduce the gas flow rate to avoid too much unburned gas, maybe I can nurse it up to 2300? I should have played with the damper/gas valve at the same time and seen if I could keep the temp climbing. In case I want to try Bab's idea, would adding a short chimney really help draw in more oxygen? How big an effect is that, and how tall should the chimney be if I want to try it? I'll give it another shot this weekend and see if I can get to 2300. As always, thanks for the good advice and suggestions! I did get to 2218 F, and as you can see from the picture (Cone 7, 8, 9, and 10 from left to right) I did get Cone 9 to go horizontal. However, I want to see Cone 10 flat as a pancake!

Folks! I finally got the natural gas line installed and did my first test fire of my mystery kiln. Loaded with shelves and cones, but no ware. To remind everyone, it's about 10 CF, with five venturi burners coming up from the bottom. No matter what I tried, I could not get above 2218 F. It wasn't a lack of gas pressure, I never even opened the valve all the way. With no damper, kiln stalled at 2218 and never went higher. I tried less gas, and the temperature dropped. More gas led to a standing flame above the vent, and the temperature dropped. I fine-tuned the gas flow for 2 hours (no visible flame, light visible flame, heavy visible flame, etc) and I just could not get above 2218. The picture on the right shows the best setting I could find, a small 6-8" flame gave me the maximum temperature. I am assuming that the venturi burners just weren't pulling in enough air to burn enough gas to keep heating up the kiln? Are there other possible causes for the I described? Do I need to try and adjust the burners? I want to get to Cone 10! Thx

Folks! Thanks again for all the helpful information. Neil, the little kiln I posted a few weeks ago is indeed the one - it's about 10 cubic feet, but I was estimating 15 CF just in case I want to upgrade or build a larger kiln one day. (My pottery mentor told me I can't be a real potter until I build my own kiln, so I am planning for the future!). Bill, those darn burners and orifices are just like the rest of my "mystery kiln" - not a mark on them, no type, no manufacturer markings, no size. I dropped drill bits down into the orifice and they are 1/8" - I confirmed the actual diameter with my micrometer. In any case, I started from everyone's useful comments and I have been doing some online homework and additional calculations. I want to fly this by everyone, let me know what you think! From reading their online material, Ward Burner Systems recommends about 10,000 - 16000 BTU/hr for each cubic foot of kiln if you are firing to Cone 10. That would mean I need 100,000 - 160,000 BTU/hr for my 10 CF kiln, or 150,000 - 240,000 BTU/hr is I want to plan for a 15 CF kiln in the future. I then tried to confirm these numbers by checking out new Olympic gas kilns from their website. Looks like their 10 CF gas kiln (Model 2827G) lists 280,000 BTU/hr on their Spec Sheet, so the Ward Burner System numbers might be for a better insulated kiln. Based on these larger numbers, I decided my goal should be to provide between 280,000 - 420,000 BTU/hr. That should make me totally safe even if I build a 15 CF kiln one day. Natural gas has about 1000 BTU/CF, so I then did the conversion to find that my pipe needs to deliver between 280 - 420 cubic feet/hr. Bill, thank you for that handy table! It made me realize that plumbers and builders don't guess about these things, they have handy tables that help them size and design piping systems for homes with boilers, hot water heaters, etc. Not sure where Bill found that table, but it's solid - I did some more online searching and found several more that have about the same numbers as Bill's table. If I take the upper limit of what I could possibly need (420 cubic feet of natural gas/hr) and then consult Bill's table, it looks like for a 60' run of pipe the 1" will be too small - I will need 1 1/4" pipe to be safe. What does everyone think? Is my analysis solid? Now Rae asked the next key question - does my gas meter have the capacity to provide another 420 CF/hr of gas if it's cold outside and my home gas boiler is firing away at the same time? My home boiler is 210,000 BTU/hr (unlike my mystery kiln, it has an actual metal plate with all the specs!), so my worst case scenario would have me needing 3 times as much gas if I was running my home boiler and gas kiln at the same time. Or maybe I tell the kids to just huddle around the gas kiln at night if the house gets too cold? Anyway, thanks to Rae! I will ask my plumber what is the maximum CF/hr that my gas meter can provide, and see if I need some kind of upgrade to my meter. Look forward to any comments or suggestions! Richard

Folks! I love this Forum, and I am glad I found so many helpful people! I don't have specs on the kiln because it is a "mystery kiln" that some of the people on this thread have been trying to help me identify. It's basically a 15CF kiln with 5 gas burners coming up from the bottom. The orifice size is 1/8", which (I believe) makes them natural gas burners. Is that correct? From the replies, it sounds like a commercial natural gas kiln is designed to be connected to a typical home natural gas line at 7" of pressure, which is about 1/4 PSI? My plumber is running a 1" pipe from my house natural gas supply out to my pottery shed, about 60 feet total distance. The gas line after passing through the gas meter and regulator is also a 1" line, so I figure using a 1" line out to my kiln won't restrict whatever flow I am getting from the meter. So basically I am hoping the kiln is designed for home natural gas pressure (1/8" orifice size), and also that a 60 foot run of pipe won't reduce the gas flow enough to matter. What does everyone think? Will I be OK? Or am I wasting my money running that natural gas line 6o feet out to this kiln?

I am connecting an old gas kiln to my house natural gas supply. Does anyone know what natural gas pressure I need at the kiln? Does anyone know the natural gas pressure in a house? Is it as simple as connecting the kiln to the natural gas line under my house, or do I need to do something else to get enough pressure? Richard

Hi Bill, your responses really helped me understand more about how things work! Super helpful. Snickerhaus - I built a pottery shed in my back yard a few years ago, and had an electrician install a 80 Amp 240 V circuit that ran from my main electrical panel on my house. While heavy gauge wire is expensive, the materials cost (wire, conduit, breakers) was less than the LABOR cost from the electrician to install everything. The lesson I learned was to plan for the most amperage/voltage I could imagine ever needing, and have the electrician install the needed wire and breakers. It cost a little more up front, but again the main cost for everything was the labor itself. Now I can move to a larger kiln in the future without worrying about doing another round of expensive electrical upgrades. Hope that perspective is helpful.

Thanks for the replies! Jeff that was a good guess, but if you can see from my (bad) pictures the lid actually rotates out horizontally and is suspended by a hinge and support. The old potter I bought it from said it was a cone 10 gas kiln, but didn't know a thing about it. Frustrating! Mark, I will start investigating West Coast Kilns and see if I can find any old models that match. This one has 5 burner ports coming up from the bottom, and the lid is attached by a rotating hinge, so I agree it's probably not from the same place that made yours. However, let's see what Google can find! Neil, thanks for the comment and suggestion about similarities to the current Olympic gas kilns. I used to fire a huge rectangular West Coast gas kilns for years, but this would be my first time firing such a small gas kiln. I have no idea how this little kiln will behave in a cone 10 firing. As a general question, who are the kiln manufacturers I should be Googling? Even old ones that have gone out of business!

This thread made me curious about #6 vs #8 wire to carry 50 amps. I found this link that might be useful, it seems to indicate that you could use the existing #8 wire for a 50 amp circuit if your distance is less than 75'.

I recently bought an old gas kiln from a retired potter, who also bought it used from an old potter. She had no idea how old it was or where it was from, but I immediately fell in love with it! Does anyone know what kind of kiln this is, who made it, how old, etc? I can't find a single manufacturing mark anywhere. It's a solid steel shell holding the soft brick, but with a strange top. Instead of a hinge that lets the top open upwards like a modern Skutt, the top is supported by a vertical steel rod and slides horizontally to open the kiln. It has an array of 5 burners coming up through the bottom of the kiln. I am including some pics, help appreciated! Here are links to some pictures: https://ibb.co/Qnh3RF2 https://ibb.co/vLXQVPD https://ibb.co/h8hmXPy