Polydeuces Posted July 22, 2018 Report Share Posted July 22, 2018 Hey y'all—been posting more often recently, thanks for all the help & tips. I recently switched clay bodies to one that has more grog (Highwater's Brownstone), which is beautiful and I really dig it. That said, it's come with some issues in the department of pinholes. To make matters more difficult, all of my firings are done in a small gas kiln (used to be electric, came with the rest of my used equipment and was in pretty horrible shape)—including the bisque. As far as I can tell, it fires pretty well, but it's 100% manual and I have reason not to trust the pyrometer. Part of the issue is when I've tried to push the bisque to 04, a lot of the pots close to an internal chimney flue (maybe it's technically a cross-draft flue?) start to get vitrified on the hot side—so it feels like a rather risky affair in terms of going hotter/longer. For now I'm intending to push to cone 05, and maybe get a little bend on 04. I'm curious how you'd go about remedying the issue if you were in this situation. Thanks~ Link to comment Share on other sites More sharing options...
Pres Posted July 22, 2018 Report Share Posted July 22, 2018 Polydeuces, Have you looked up a color/cone /temperature chart. This could get you a handle on your temps. I fire an electric with not setter, and no controller. . . all by hand. This is my best estimate, and then I use cones to fine tune each of my firings. At to you pin hole, are you firing to recommended bisque temp for the clay body? Link to comment Share on other sites More sharing options...
preeta Posted July 23, 2018 Report Share Posted July 23, 2018 I don’t have any answers - curious to read what others say - but I have more questions. Are you assuming the hot spots near the flue gets hotter by one cone? Next time I would put cones in the hot spot to see what the temperature difference already is. One cone difference I would imagine would not create the kind of vitrification you are describing even though it is on the inside of wares. is your glaze firing in oxidation? What is the state of the bricks inside? Or liner? propane or natural gas? Newbie to firing myself. Learning how to identify flame and pyrometer reading. Link to comment Share on other sites More sharing options...
Polydeuces Posted July 23, 2018 Author Report Share Posted July 23, 2018 Thanks for the responses~ Pres, that chart you provided is helpful. Unfortunately my kiln has a whopping two peepholes and I can rarely if ever see any pots in there. Though, I'm considering the merits of drilling a couple extra for more visibility & the ability to vent it a little better at different stages of firings. I was unable to find any specific info on recommended temps for the clay body I'm using, but I'm planning on tackling it from multiple angles. (More oxygen, longer, hotter) and see where that gets me. Preeta, thanks for your questions. 2 hours ago, preeta said: Are you assuming the hot spots near the flue gets hotter by one cone? Next time I would put cones in the hot spot to see what the temperature difference already is. One cone difference I would imagine would not create the kind of vitrification you are describing even though it is on the inside of wares. I'm pretty darn certain it's hotter. I attempted bisque firing to cone 04 a couple times, and pots that were near the internal flue were roasted on the side facing it. They had visible discoloration, and those areas on the pots wouldn't take a glaze that was around 1.2sp. That said, I'm given to think you're right about placing some cones and being certain. It may be the case that I must avoid placing any pots in that area during bisque firing. 2 hours ago, preeta said: is your glaze firing in oxidation? No, it can get pretty heavy in reduction. I'd like to be able to vent it a little better, but ultimately I get to thinking that my chimney/burner ports sizing may be a whee bit off, or my chimney is too narrow. Not really sure. 2 hours ago, preeta said: What is the state of the bricks inside? Or liner? LOL. Pretty rough. I think this kiln was used only for bisque prior to it being passed along to me, but even in 3 years it's taken a beating while I've been figuring stuff out, drilling holes in it, etc. It's a smaller kiln, an old "Jenken" electric kiln... I'd estimate maybe between 4-6 CU ft. I'm firing with propane currently. Link to comment Share on other sites More sharing options...
preeta Posted July 23, 2018 Report Share Posted July 23, 2018 P I researched your clay online last evening and I noticed it always talks about oxidation. While nowhere does it say “not for reduction” I find it’s lack of interesting. What is interesting is it doesn’t say anything either about reduction with speckled brownstone either. On the west coast we are spoiled by our claymakers. Most of the big common ones show both oxidation and reduction test tiles or have an advisory against reduction. Here a similar speckled clay body specifically says not to be reduction fired. I still tried it to see what happened and yes shouldn’t be reduced. Iron clays don’t do well in reduction. I wonder if that has anything to do with pinholes. Our local clay company says reduction at your own peril with red claybody. I’ve actually mixed with white claybody to reduce iron content to see if it has any impact on carbon coring. It did. I wonder if the state of the kiln is adding to temperature differences. Where are your burners located? Is a new kiln or used kiln in your future plans? What kind? I mean if you plan to get an electric kiln all this research will be moot. But if you plan to continue with gas then it’s worth it. I know propane burns differently than natural gas. Hotter? Did you notice from which areas of the kiln you were getting pinholes or was it all over? It’s always good to know the cold spots and hot spots in your kiln. Is 4-6 cu ft a test kiln size? Link to comment Share on other sites More sharing options...
Polydeuces Posted July 23, 2018 Author Report Share Posted July 23, 2018 5 hours ago, preeta said: P I researched your clay online last evening and I noticed it always talks about oxidation. While nowhere does it say “not for reduction” I find it’s lack of interesting. What is interesting is it doesn’t say anything either about reduction with speckled brownstone either. On the west coast we are spoiled by our claymakers. Most of the big common ones show both oxidation and reduction test tiles or have an advisory against reduction. Here a similar speckled clay body specifically says not to be reduction fired. I still tried it to see what happened and yes shouldn’t be reduced. Iron clays don’t do well in reduction. I wonder if that has anything to do with pinholes. Our local clay company says reduction at your own peril with red claybody. I’ve actually mixed with white claybody to reduce iron content to see if it has any impact on carbon coring. It did. Interesting—I hadn't really thought about that aspect. I'll send them an email to check in as to any technical info I can acquire (and will post here). I'm fairly certain that, in the warehouse I had seen a reduction tile—but perhaps I'm mistaken. Either way, it would be a damn shame if I'm simply using the wrong body for this. It just looks...so...nice. 5 hours ago, preeta said: I wonder if the state of the kiln is adding to temperature differences. Where are your burners located? The burners are underneath the kiln, pointing up. It's just two weed burners. 5 hours ago, preeta said: Is a new kiln or used kiln in your future plans? What kind? I mean if you plan to get an electric kiln all this research will be moot. But if you plan to continue with gas then it’s worth it. I'm not really certain what direction I'm going into in the future. My aims, thus far, have been to get my process worked out with what I currently have. My current space doesn't really allow for an electric kiln, and I have mixed feelings about putting one outside (though I do have rain coverage). If I could find a bigger old junky kiln for very inexpensive (prefer free!) I might try and run that. A digital kiln would be excellent, though. Running small firings on gas is kind of exhausting. 5 hours ago, preeta said: I know propane burns differently than natural gas. Hotter? I'm not really certain—I've never fired with natural gas, but I would imagine hotter. My understanding is that the pressure on propane can be pretty high—I think natural gas is very low pressure, though that's some vague recall. 5 hours ago, preeta said: Did you notice from which areas of the kiln you were getting pinholes or was it all over? This past glaze run, it was all over. Previously I've ran a glaze fire with this clay body, and aside from some negligible pinholes, it came out pretty clean. It did not happen with a lighter (grogless) body I had been using (which was even glazed thickly with a rutile glaze). 4-6 cu ft is I think technically in a "medium" size. It's not quite a test kiln. On a glaze fire, after having cut the shelves to allow for airflow, I can probably fit about 20-30 pots in there (depending on size). Link to comment Share on other sites More sharing options...
Callie Beller Diesel Posted July 23, 2018 Report Share Posted July 23, 2018 @Polydeuces Is your bisque also going into reduction? How tightly did you pack the bisque that the pinholed wares came out of? Link to comment Share on other sites More sharing options...
Callie Beller Diesel Posted July 23, 2018 Report Share Posted July 23, 2018 21 minutes ago, Polydeuces said: I'm not really certain—I've never fired with natural gas, but I would imagine hotter. My understanding is that the pressure on propane can be pretty high—I think natural gas is very low pressure, though that's some vague recall. The pressure on natural gas is indeed lower, but that only matters when you're talking about burner orifice size, pipe diameter and number of bends in said pipe. Burning hotter or colder is a bit academic: burning enough of either propane or natural gas in the correct atmospheric conditions will get you to temperature. Link to comment Share on other sites More sharing options...
Polydeuces Posted July 23, 2018 Author Report Share Posted July 23, 2018 @Callie Beller Diesel, thanks for the clarification! I'm always learning something. To answer the more operative question—I have been stacking my bisque pretty tightly. I'm pretty sure the kiln hasn't gone into reduction during bisques, but I guess there's no way to be certain, as I don't have an oxygen probe. There's no flame emerging from chimney nor peepholes, so I suppose that's a plus. So far, my first plan of attack goes with the following procedure: Drill some extra peepholes for visibility into different levels of the kiln, and leave them open during bisque firings. Add some cone packs into different areas of the kiln. Pack a looser bisque. Any parameters around this? Like, how many bowls can I nest safely? Shoot for a higher cone, (I'm thinking I'm going to place an 05 & 04 in there, and wait til the 04 just starts to bend). Soak for half an hour? Keep the gas pressure as low as possible. I've got some leftover bisque from the last firing. Some of the pieces have been glazed, but I'm thinking I'll just rinse them off and have another go with them. (Bad idea?) Link to comment Share on other sites More sharing options...
Rae Reich Posted July 24, 2018 Report Share Posted July 24, 2018 I think you can make a mini bag wall from a brick or two or a propped up piece of kiln shelf to protect that hot spot. I've had that scorched side on pots too exposed to flame and they don't absorb glaze as well there. Regarding Pres' pretty color chart, you don't need to see the actual pots being that color, you're looking for the color of the atmosphere. If it's too murky while you're trying to climb, you're reducing, and working against the climb. Change air/gas balance. Link to comment Share on other sites More sharing options...
Polydeuces Posted July 24, 2018 Author Report Share Posted July 24, 2018 Hey Rae, thanks for those tips! I'm curious about the bagwall thing. I have a "floor shelf" and on the actual floor of the kiln are two rows of bricks (running parallel) from the chimney flue to the opposite side of the kiln. Basically there's a "port" raised on top of those bricks—so the gases enter the port, run horizontal underneath the shelf, and outside the chimney. The pots sitting on the floor shelf, next to that "port" are the ones that get extra toasty. My curiosity is the placement of said bagwall, and if it would disrupt the movement of the gas? I'm not entirely sure how to adjust air/gas balance with my current setup. I'm running two weed burners. There is a needle valve at the Y splitter on the propane line, and each burner has a flow control valve. Other than that, it's just an adjustable regulator. It's something I've been curious about for awhile. Firing this way, I usually start with low pressure, open the flow valves on each of the burners in the early stages, and then increase pressure, which usually happens around 1800-2000F. Is there a different method that's recommended? Generally I treat the pressure as the primary means of controlling the gas level, but I can't necessarily "inject" air, at least not to my knowledge, without a blower fan. I originally ran with a squirrel cage fan & iron pipe setup, but found it very "cannon-like—" it made me nervous as hell, and I dare say it was very challenging to get a low flame at the early stages of a bisque fire. Link to comment Share on other sites More sharing options...
preeta Posted July 24, 2018 Report Share Posted July 24, 2018 P I am learning about gas firing at a community college. I am lucky. I have a teacher who has done a lot of different firings. So I use all my senses while figuring out reduction firing. Not just sight. But taste , smell and sound too. I use my senses to guess and then check the cones and electronic equipment to see if I am right. So if you can’t see the sound of the flames and bbq burning smell and taste tell me the kiln in reduction . Do you have air going into your kiln? An air line that you can control? How do you set your kiln into reduction? Do you have flues to close? Do you body reduce? At school we have a large gas kiln that is a dedicated bisque kiln and never reduced! Link to comment Share on other sites More sharing options...
Polydeuces Posted July 24, 2018 Author Report Share Posted July 24, 2018 1 minute ago, preeta said: P I am learning about gas firing at a community college. I am lucky. I have a teacher who has done a lot of different firings. So I use all my senses while figuring out reduction firing. Not just sight. But taste , smell and sound too. I use my senses to guess and then check the cones and electronic equipment to see if I am right. So if you can’t see the sound of the flames and bbq burning smell and taste tell me the kiln in reduction . Do you have air going into your kiln? An air line that you can control? How do you set your kiln into reduction? Do you have flues to close? Do you body reduce? At school we have a large gas kiln that is a dedicated bisque kiln and never reduced! Oh dear, if I should be so lucky~ No air lines or any means of injecting air. I use a loose brick in the chimney stack to damper the chimney, usually as it is getting close to peak temperature. I've experimented with reducing earlier for body effect (if that's what you mean), but have found that it can be tricky to get it to climb once the brick is in place. I wish I had a separate bisque kiln. It'd make life a lot easier. I'd totally get a used electric kiln for this express purpose, but I have no where to put it. ¯\_(ツ)_/¯ Link to comment Share on other sites More sharing options...
Rae Reich Posted July 24, 2018 Report Share Posted July 24, 2018 The little "bag wall", being just a bit of shelf or brick that the flame hits instead of the pots would not obstruct the gasses any more than your pots do. Arrange pots away from direct flame. Sorry I do not have experience with air intake when using weed burners and propane. I have natural gas. Venturis on the big kiln and a squirrel cage on homemade pipe burner on my little one. Link to comment Share on other sites More sharing options...
preeta Posted July 24, 2018 Report Share Posted July 24, 2018 6 minutes ago, Polydeuces said: Oh dear, if I should be so lucky~ Oh P you ARE lucky because you are really learning how to fire the kiln. I wish I was in your shoes to really understand the philosophy of firing a kiln. I feel I am spoon fed here so have to create my own challenges. I didn’t read your reply to Rae so did not read about your squirrel cage fan stuff! Wow! Link to comment Share on other sites More sharing options...
Polydeuces Posted July 24, 2018 Author Report Share Posted July 24, 2018 @Rae Reich Okay, thanks for the clarification. I feel fairly certain that it's not the flame from the burners that is causing the issue, as pots on the center of the shelf are the ones getting toasted. The burners are underneath the kiln, pointing up and on either side of the shelf. To clarify, it's the side of the pots that are facing this "extreme hot zone" where all the gases in the kiln are collecting and making their way, under the floor shelf, across the kiln, and through/out the chimney. The arrangement lined up conveniently with the floor's peephole, and you can see the flames barreling down this horizontal channel toward the chimney—it's pretty exciting to watch! All that said, I worry that if I were to cover this port, or obstruct it in anyway, it would obstruct the gases from leaving the kiln and I'm not so certain if that would be helping the issue or not. Maybe it would! I don't know pyrodynamics enough to really know the best placement to safeguard pots that are close by, without obstructing the exit of the gases. @preeta I suppose in some ways, I am. I feel like a masochist more than anything else. I've been through a lot of tests and I feel like I'm getting closer to making this pottery thing work, yet all the while I can't help but feel as though I'm just kicking the waves of the ocean, if you know what I mean. Link to comment Share on other sites More sharing options...
preeta Posted July 24, 2018 Report Share Posted July 24, 2018 I understand! I have two passions in life. Pottery and cooking. Because I don’t follow rules but create problems and try to solve them. The moment I know for certain I lose interest. In a way every pot/item I make is an experiment. Things don’t happen easily to me. I struggle but stay tenacious and then boom, like turning on a switch it all makes sense. Mind you tho’ my brain takes its sweet time to make the connection! i really appreciate all the discussions and digressions here because I learn so much! Link to comment Share on other sites More sharing options...
Polydeuces Posted July 24, 2018 Author Report Share Posted July 24, 2018 Brief update. I contacted highwater and they said that it's not ideal for reduction because of the iron (but agreed it looked very nice) and recommended I smash a few pots to inspect for carbon coring. Based on pictures I've seen in relation to carbon coring, it appears to have none of that going on. Making some "educated" guesses, I would guess that it's #1: Bisque temperature & duration. Probably the easiest go-to at the moment. #2: Ventilation. #3 Tight bisque packs. Will update with any results in the coming weeks. There are only a couple days a week I can fire, and the pots are on their own schedule. Thanks for all the advice & support, y'all. Link to comment Share on other sites More sharing options...
tomhumf Posted July 26, 2018 Report Share Posted July 26, 2018 Just to throw a spanner in the works... Aside from your bisque ideas, does your pinholing occur on all glazes? Maybe try some other glazes, or try longer glaze firing to see if the pinholes heal over? Link to comment Share on other sites More sharing options...
neilestrick Posted July 27, 2018 Report Share Posted July 27, 2018 On 7/23/2018 at 9:34 AM, preeta said: On the west coast we are spoiled by our claymakers. Most of the big common ones show both oxidation and reduction test tiles or have an advisory against reduction. Here a similar speckled clay body specifically says not to be reduction fired. I still tried it to see what happened and yes shouldn’t be reduced. Iron clays don’t do well in reduction. I wonder if that has anything to do with pinholes. Our local clay company says reduction at your own peril with red claybody. I’ve actually mixed with white claybody to reduce iron content to see if it has any impact on carbon coring. Cone 6 clay bodies that are intended to be fired in oxidation require a lot more iron to get them to go dark than do bodies that are intended for reduction. Iron is very reactive when reduced. So if you reduce one of these high iron bodies, there's just too much iron reacting and the bodies can be very brittle, or bloat, etc. Link to comment Share on other sites More sharing options...
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