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MartinB

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  1. What Min said, try glazing with only one glaze on both the inside and out, it might be that the glaze is not that compatible with your body. It could also be that you have different amounts of glaze on the inside vs the outside depending on which you dipped first. The body absorbs some water with the first one, then the second application doesn't draw as much water so you end up with a thinner coating. You could make sure the body is completely dry after the first dip, or give the second dip more time to build up a thicker coating. Depends on the thickness of your body, what temp you bisqued at etc Its a process of elimination. Good luck! Edit: Do you have a link to the glazes? Am curious about them being compatible...
  2. Have a listen to this podcast - Building a Community Center | Tallie Maughan | Episode 249 http://thepotterscast.com/249 Its the place I started doing pottery at in London, its gone from strength to strength and is a real hub for ceramics in the city now, they're even opening a second site too. Might not transfer over to what you're thinking but definitely worth a listen and probably some useful advice.
  3. I did see Cool Ice (^6 porcelain) listed on potclays website but its out of stock and £51 for 9.25kg!
  4. If only it was available in the UK I'd jump at it.
  5. Most online suppliers have a section for cone-6 glazes but pretty much all clays are just listed as stoneware and given a broad firing range. I'm interested in a cone 6 porcelain but there are none listed specifically as that, though several say 1240-1300 firing range. I assume at the lower end I would be sacrificing some translucency and strength... I've ordered sample packs of a few and am going to run some tests. I'm happy enough re-formulating my glazes to work at cone 6 but if I can't get a nice body I'll have to stick to higher firing.
  6. Yeah I've seen very few cone 6 clay bodies that aren't sold as firing from cone 6-10. Keep reading posts here about beautiful translucent cone 6 'Frost' porcelain but there's nowt in the uk.
  7. If you found the video interesting and want to know more about glaze chemistry and what all those numbers mean when you look at insight-live or glazy.org I couldn't recommend highly enough the Glazed and Confused course offered by Matt. Crazy amount of well presented information and a stupidly low price. I've had a vague understanding of what the numbers mean from reading various books and online articles but never explained so clearly in such depth with loads of diagrams. In no way affiliated but now a massive fan boy, hope you continue to release all the future courses you hint at.
  8. Thanks Matt, really interesting. Just signed up for your U.M.F workshop, looks a bargain for $10 and nice to see some technical tutorials!
  9. MartinB

    Math Problem Is Beyond Me

    Make up two more 8000g base glaze batches, giving you 24,000g in total, this should knock the 0.75% chrome down to 0.15% (you would have added 36g instead of 12g of chrome to the 8000g batch to make 0.75%) You'll need 3x10,000g buckets to contain the 24,000g EDIT: my %'s were wrong, listen to 123pop
  10. MartinB

    Colour Response Of Base Glazes

    So the two new glaze bases came out the kiln this morning and they definitely improved the colours, though I foolishly didn't label them correctly so don't know which was the higher sodium and which was the higher boron. The copper at 0.1 percent looks good and matches the colour of Linda's Runny. The Chrome at 0.1% didn't go as bright as Linda's, but definitely looks better than the dull previous tile and these were 100g batches so not sure how accurate my 0.1g addition was, and the Purple Stain is now working again. All in all I'm happy, learnt a ton about glaze chemistry along the way Chrome at 0.1% Copper at 0.1% Purple stain at 4%
  11. MartinB

    Glaze 101

    I'd recommend this, or one of his books depending if your high or mid firing. A wealth of information in both books, the video covers a lot of the same ground with a few extra bits thrown in but it well presented and easy to watch (although the background music gets really annoying after a while!)
  12. MartinB

    Tips On Using Porcelain

    Thought I'd jump in on this thread. I'm curious how other's prepare porcelain for throwing? I've been using Audrey Blackman for a few months now (after throwing with stoneware for a couple of years) and out the bag its very soft and flexible. If I wedge on a wooden table it doesn't firm up much, and if I wedge on a plaster bat it starts to crack or get short after a few pushes. I had a bit of a revelation today, I was throwing with Earthstone Glacier for the first time and it was a similar consistency as the AB out the bag and if wedged on a plaster bat was splitting etc. After having a couple of bowls collapse I put the resulting sloppy mess on a plaster bat and came back to it after about 10-15 mins. I wedged it up and it was firm without cracking/splitting, I then threw with it and managed to pull some nice delicate walls that didn't collapse. No one else really throws with porcelain at the studio I go to so asking questions like how firm it should be and how to prepare it properly is difficult. So, how do you know your porcelain is 'ready' for throwing? Any help is much appreciated. Martin
  13. MartinB

    Colour Response Of Base Glazes

    Thats what I originally thought but from what the others have said and some further reading higher sodium content can give a good colour response turning Copper turquoise and Chrome a strong greeny/yellow, which is whats happened with my test tiles I think. Linda's base is high in Sodium and low in Potassium, and the digitalfire base is the opposite. So I'm trying to push the digitalfire base towards Linda's, but without going too far (I don't want a really runny glaze). I think the Boron still has something to do with the colours so going to try that too. The rest of the ingredients and amounts of them aren't drastically different, so its got to be the amounts and ratio of the fluxes.
  14. MartinB

    Colour Response Of Base Glazes

    Thanks for the input guys. I've been learning Insight Live this evening and have formulated 2 variations on the digital fire base. One that introduces some boron (about half the amount of Linda's) while keeping the Ka2O and Na2O similar. The other that lowers the Ka2O and increases Na2O and has a very small bit of boron. Was a case of changing some of the feldspar's and using a little frit. The Si:Al ratio, Calculated Expansion and CaO values have stayed pretty much the same as the original recipe, was fun trying different ingredients and balancing everything out. Will be interesting to see what the change in flux ratio does to the colour response and viscosity, I'll post results when they're done but might be a couple of weeks.
  15. MartinB

    Colour Response Of Base Glazes

    I've never tried CTM but looking now they are substantially cheaper on a lot of things. Bath Potters is my go to place as they're just down the road so I can go collect, but then if they're twice the price it'll still work out cheaper shipping from CTM. Cheers! I didn't post the recipe as I wasn't sure on the etiquette of posting something from a bought source, its a relatively new book out so didn't want to tread on any toes, but yep you're right, it has approx 15% Calcium Borate Frit, so the actual amount of Boron is dwarfed by the massive amount of Soda Feldspar. Thanks Diesel Clay for the Sensible Shoes vs Party Shoes analogy Makes a lot of sense and a great way to visualise it. In my head the feldspars didn't have much to do with colour response and were just a general base, and when talking bright colours I think of Barium, Strontium and Boron. The purple stain has thrown me a bit though, I'm pretty sure its not to do with Magnesium in the ingredients as I actually did a chrome/tin oxide test of both Linda's base and the digitalfire base and they produced similar results, apart from Linda's looking a bit nicer. Though I only tested the bought stain in digitalfire's and a commercial base. A brief search shows that purple stains are normally chrome and tin so it'll take some more investigation. I've attached a photo tagging which is which. You were also right about the Kaolin amount, Linda's only has about 5% which now sounds very low. So on with more testing, introducing some frits and hopefully I'll end up with some sensibly party shoes. Will also be a good time to figure out InsightLive. Thankfully the studio I'm at has most ingredients you can use for testing so I don't have to commit to a big batch order yet.
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