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About tomhumf

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    Sheffield, UK

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  1. Bill, I just wanted to thank you for your very generous reply. I will go through all that in detail when planning my next firing. Need some time to process everything I think. Will let you know how I get on. Many thanks!
  2. Sorry that video was just meant to show the kiln design. I've uploaded one from my firing since I started this thread. The clip is during my body reduction phase. I fire in oxidation until body reduction phase, when I close chimney to about and inch and increase gas. I start this at around 940 °C and reduce like this for and hour, usually climbing to about 1000°C . Then I try to fire neutral / light reduction to cone 7. In the last firing for this stage I opened the chimney a few more inches and reduced gas until the flames were just not coming out of peeps, but still a chimney flame. I'm trying to follow advice I've read by Neilestrick although I've just realised I should probably start body reduction sooner according to him. - " Get up to body reduction temps- cone 012 to 08- as quickly as you can while not cracking any pots and maintaining evenness. No sense wasting gas with a really slow climb if everything has been bisqued. Put the kiln into reduction at cone 012-08, and stall out the climb. Hold temperature with the reduction for 45 minutes. If you're trying to carbon trap a shino glaze, then make this a heavy smoky reduction. Then put it into a neutral atmosphere and let it climb to cone 10. Stalling it out in reduction will ensure that you get good reduction throughout the kiln, and climbing in a neutral atmosphere will give you an efficient use of gas." The reduction was better but this time but the top fired a fair bit cooler ( about a cone) than the bottom. I seemed to have the gas up very high during reduction this time. Perhaps I should close the chimney more to allow less gas to create the same sized peephole flames... I'm a bit confused about what effect this would have. Not sure what you mean by "allowing wares to see each other " I've googled celosia red but just get loads of plant stuff. Is it a glaze or something? Thanks And yes I should have put my gloves on - good job I've got chefs fingers.
  3. Thanks, I cover most of the design in the thread I link to in first post. I'll add a video below it covers most of the details in first 2 minutes. Basically it's one burner, not much area around the shelves for flames - they are all same size as the bottom one in video and stacked to the top. Not sure about pressures, my regulator is set to 1 bar I think and I adjust the needle valve on burner as I'm firing. I'm firing to cone 7 which usually takes about 7 hours. It fires fairly evenly top to bottom but slightly hotter at bottom on recent firings. The video was first ever firing. I'm now doing a bisque firing in about 5 hours total.
  4. I've struggled to fire my little ( about 3 cubit ft?) Gas kiln for just over a year. I'm finally starting to get results I like. One problem was what temp and time to reduce at. I've found that reducing hard between 940C and 1000C for one hour is giving me the best results for my glazes. I reduce by increasing gas and blocking the chimney to about 1" opening. I used to then open the chimney fully to complete the firing. I've finally figured out this is why (I think) I ended up with a lot on pinholing on quite a few pots out of each kiln. I think there was a large temp difference between different locations in the kiln. For the last few firings I have reduced hard as before, but closed the chimney to half open to complete the firing. This gives a flame from the chimney but not from the peeps like during hard reduction. Firing this way means I get hardly any pinholing - just one pot usually on the bottom shelf right bear the burner entry. The main problem with the last few firings is the reduction on the top couple of shelves is not very good. Is this a common problem? And are there any tricks to get good reduction at the top as well as the bottom? Thanks
  5. Wow this got a lot more feedback than I expected! Seems the consensus is the firing is unlikely the cause, more probably the manufacture. This batch was some mugs with custom name stamps added on a round of clay. Something new for me. I did some re-wetting of the mugs with a spray bottle. This has never been a problem before but maybe I stressed them and caused cracks when they had got too dry. And stamping the letters may have been too rough. I'll just try and work with them wetter and carefully going forward and see if I have any more problems. Thanks
  6. I've never had a problem with cracking before. Last firing 3 mugs had similar looking cracks, this being the worst. I'm trying to understand what's caused it. Its the same clay and glaze I always use. Firing was same schedule. The only thing I can think was it was a cold night when I turned the kiln off. I close the chimney and peepholes but leave the burner port open. I don't down fire the kiln after final temp and it's small gas kiln - about 3 cubit ft. I've not had a problem before but maybe fast cooling is the problem? Any ideas welcome...
  7. Thanks, I'm still early stages, I'm in the UK though and I guess you're US.
  8. Ok thanks. My plans for burner port is currently 3" X 4" opening. I plan the chimney at 6" X 6" inside with 3" thick walls.
  9. I've had to put this on hold due to money but, now have the funds ready... This is my latest plan after your suggestions and some other reading. 9" thick walls, will probably do 4.5 " arch with fiber over the top and 9" thick floor. I'm hoping to make it work with one burner, my biggest concern from this plan is the space around shelves. It's probably a bit tight top and bottom ( 1½" ) and too much at the flue side (4½") but can't see a better way without having to cut a load of bricks. I plan 8 courses for walls, which would give about 10cu ft total internal space with arch.
  10. @Bill Kielb Thanks so much, will have to re read that a few times for it all to sink in I think! Lots of good stuff
  11. It's iron Great video, is the longer version online somewhere? Id be interested to see it if so. I have a couple of questions... the attached photo is of my latest firing. Same glaze but a bit more frit this time, all the mugs were in same firing. I'm wondering if the differences in look is because I didn't ' fill the kiln and not have any dead spots' like you say. In this firing I reduced between 1600F and 1900F, and was in oxidation ( I think ) after that up to cone 7. I will probably try and follow your schedule next time, and maybe reduce more in your heavy reduction section. I'm a bit unsure of how best to get the temp to climb while under heavy reduction. My method of reducing my little electric kiln conversion is to shut off the chimney to about 1 inch gap. This creates a reduction flame out of chimney and peeps but makes it hard to gain temp - I understand this is because its burning inefficiently. But if I increase the gas burner power it's just going to burn more inefficiently? ...but if i reduce gas it will go back to oxidation I guess I'm missing some of the control of larger kilns, and I don't really understand the terms primary and secondary air. From what I understand they the air mixed at burner port (primary) and air available at chimney (secondary) ? Wish I could get an oxy probe but no budget for that unfortunately. What happens if you reduce under 1400? Not that I want to but seems like something really bad would happen...? @Mark C. I understand your point about cold spots / oxidised spots. Hopefully I will be able to minimise them in some way, I guess a lot is down to kiln design which probably isn't great in my case. @neilestrick I'm stuck with gas firing really at the moment. I understand every pot won't be the same. I'm happy with 75% of the pots out of this lot, just wish I could prevent the really boring white ones ( like 3rd right and 3rd left) in the photo.
  12. Lots of Dremel love here, I will get one I think. Not sure about them being expensive, the low range ones are £60 / ~ $70? On Amazon...I suppose compared to knock offs they are expensive?
  13. Ocassionally I unload the kiln and find some little chunks of glaze/ clay / god knows what on my pots. This is despite looking over/ sanding the bisque carefully, sieving glazes etc. I'm thinking of getting a Dremel to tidy up these sharp lumps. I don't currently have anything like a sander or grinder. I only grind bases with sandpaper or rubbing two pots together. If you think dremels are a good idea, what kind bits would I need? I'm looking at the Dremel 3000 which has a few included. I guess you need a hard rough one to remove material then a polishing bit? Thanks!
  14. I can see how you think glaze thickness is the issue. I have keep glaze the same, and same dipping time for ages while trying different firing cycles. I thought the thickness might be an issue myself and thinned the glaze a little for the one on left. Not sure if that means thicker glaze would be better....but I've had plenty of bad results with the previously thicker glaze too. I will try take a pic before i go on holiday of the bases, they are very similar. The right one is very slightly darker but not really dark like on the plate base.
  15. I've been struggling with this glaze for a while, I really like it when it works... It's a speckled clay with white glaze I've developed on all these photos, fired in a tiny gas kiln. I like the mug on the right - the glaze breaks on the rim, handle and throwing lines, and there's a bit of speckle showing. I don't like the left one at all, the glaze is melted but very boring. I like the yarn bowl results - similar to the right mug. These have all been fired with between 30 mins and 1 hour reduction at around 1500 F - then completing the firing in a neutral atmosphere. I've played around with a lot of schedules. Some just holding on reduction at around that temp, some climbing through it in reduction. I can't seem to pin down what temp or amount / length of reduction is giving this look. Perhaps it's more to do with final temperature though I've aimed to fire everything to cone 7 consistently. The plate was done in the one firing where I began reduction at 1800F and stayed in reduction until the end of firing. I don't like this look as much. Although the speckle is very pronounced I don't like how the glaze has lost its whiteness. ( I think I may have splattered iron on the surface and painted the rim with iron on this one, so not a perfect comparison) I've started making better notes in my firings, but maybe someone might know if the look I'm after is to do with reduction or simply temperature? Or any other hints Thanks!
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