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About tomhumf

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    Sheffield, UK

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  1. I'm just remembering when I glaze them, a couple of them were really bubbly on the surface, which I smoothed over. I think the top of my bisque was a bit underfired , possibly where these mugs were so maybe this has caused it...
  2. Right. I'm wondering next time whether to try body reduction - neutral/ ox phase then back into reduction...or just live with top firing colder than bottom. Ok ill try that. It was around 8 hours glaze firing so not super short for my little kiln
  3. See image attached. I've never seen anything like this before but last two firings I've had it on 2 different glazes. It occurs are the same spot in kiln ( at the base opposite burners - this seems to be a colder spot. ). I'm firing a very small gas reduction kiln. The bubbles are super thin and crack if you touch them, underneath the glaze seems to be melted fairly well. The only thing I can think I changed on last two firings is I added a neural / oxidation phase near the end this has got the top of kiln up to temperature better. Also maybe my bisque has been a bit short... So any ideas what's caused it, and if you think refiring them will smooth over bubbles?
  4. I agree with what you say - just had to point out that dog dishes are one of my best sellers at the moment Don't underestimate what people are willing to spend on their pets
  5. I've recently made some beer tankards with the idea of 'traditional English tankard' in mind. They look fairly similar to the Leach tankard style, perhaps because I've been a fan of their pottery, and Simon Leach YouTube channel. I was wondering if Bernard leach invented the style - I guess it was based on previous designs he had used. I've done a quick Google on the topic and haven't found much apart from Wikipedia. Does anyone know of any good history articles / books on ceramic tankards? I would feel better making them if I'm carrying on a long English traditional method rather than just nicking someone else's idea!
  6. Ok sure. No I'm working to cone 7 in reduction at the moment, is there some reason you shouldn't do that?
  7. Thanks all. I can't get any visible cutlery marks on the black one. The white does cutlery mark but not very easily and rubs off unless I attack it superhard with a knife. I've started using Zirc as an opacifier as I want a bright white in reduction. Previous tests show 7% is still quite white so I'll drop it down to that. Failing that I suppose I could flux more to reduce cutlery marking? It's not really a big problem but I'd prefer it not to happen. I'll make up some plates and do some more testing like your suggestions.
  8. I'm working on a new raw glaze recipe. https://glazy.org/recipes/60373 Seems to be good so far, it's within the green and cooper limit formula for cone 7, and doesn't seem to scratch at all. The attached photos are with additions of 10% zirc silicate, and 10% black iron oxide ( not mixed very well) . The black one has patches of very matt surface. I'm wondering if this would be a problem for dinnerware surfaces?
  9. Oh thanks, I just look at the digital fire page for zirconium though and it has a comparison with tin. Looks like tin doesn't stay white in reduction so I'll probably not try that one.
  10. I've been using a glaze with 7% titanium dioxide as an opacifier over speckled stoneware. It's very white when fired in oxidation conditions but goes more tan / grey in reduction. I like the look of the clay in reduction and I seem to get less pinholes for some reason in my small kiln. So I'd like to change the opacifier, going to try zirc silicate and tin. I just wondered if anyone knows which ones ( if any ) will produce a very white glaze even in heavy reduction? Thanks
  11. I didn't realise when I started out how much the same type of clay varies from the supplier ( mine anyway) . Sometimes it's perfect, the last batch has been so stiff it's hard to wedge. Not something a beginner would realise that they might have to wedge some softer clay together with harder to get a good consistency. I have got bags before with loads of finger holes poked in the clay with water added to the bag, obviously it had firmed up too much. Occasionally it has been too soft and I need to wedge it up on a plaster bat for some time.
  12. 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!
  13. 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.
  14. 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.
  15. 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
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