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Everything posted by Thrown_In_Stone

  1. The Bisque is a medium speed cone 04 on smooth white stoneware. Potters Choice glazes brushed on fired to cone 6 medium speed. The glaze is perfect after the glaze firing. The only defect is after the decal fire for which the firing schedule is 250ºC/hour up to 830ºC with a 15 minute soak, natural cooling.
  2. Hi everyone,. I usually fire little decals with my logo on to the bottom of every ceramic item I produce. I have just moved from Earthenware to Stoneware after having had excellent results with Earthernware decals but after doing the decal firing on stoneware I am getting pinholes and bubbling all over the stoneware glazes (not just on the decal but everywhere). I have followed the firing schedule my decal supplier has advised which is 250ºC/hour up to 830ºC with a 15 minute soak, natural cooling. The colour of the glaze also changes slightly. The stoneware is cone 6. And the glaze is mostly Potter's choice to ^6. There are also other brands of glaze which is affected. Any Advice? Would you increase the temp of the decal firing in the hopes that it will heal over the pinholes or reduce the decal temp in the hopes that it will stop the glaze melting so much. (And what temperature would you recommend). Thanks for any help you can give.
  3. Thanks for your comments. I actually like the vase too, In fact it's in my kitchen filled with water to test if it leaks (being earthenware), If it doesn't I'll be selling it or at least using it for myself, looks like it should have come out like that! I should note that I wasn't best pleased as this is my brand new Skutt kiln; 3rd firing ever (fist glaze firing). However I know this isn't the kilns fault as it did it in my old one once, not quite the same glaze combo but almost the same. Thankfully not too much damage to the kiln, most of the glaze came off the batt wash with only minor grinding needed. Also ran off the shelf onto the bottom slab which after removal left a 1cm deep hole in one of the bricks *SOB* . Though I'm extremely thankful that it wasn't worse, as one of the splashes was 15mm away from the bottom element groove (how lucky am I?). The glaze in the mugs is not the white, it's transparent but almost identical base glaze. I'll try find the recipe for the blue and post it later.
  4. Well, I seem to have found one of my famous explosive glaze combinations again. I have 2 glazes (Blue and white) The blue is fabulous, it's never let me down but I tried putting a white over the top of it this time and OH MY DEAR GOODNESS. I attach a picture of the the result in in the kiln and one of the pots. The glaze doesn't seem to have run off the pot, more fallen off; I just don't know at what point during the firing though. The recipe for the white is: Calcium Borate Frit: 39 Soda Feldspar: 27 Whiting: 5 China Clay: 6 Quartz: 23 Zirconium Silicate: 10 Cone 04. Any ideas? Is there ingredient that may be in the Blue glaze that the zirconium it's reacting badly with?
  5. Hello, I have just bought a new Skutt kiln and wondered what setting I should use for bisque. I'd like to use the cone firing mode but should I use the slow setting with no pre-heat, or the medium with a 1hour preheat (which is 60ºF per hour up to 180 then hold fir 1 hour). My greenware is dry. Thanks for any advise you can offer.
  6. I think with the right glaze and flux, you should be able to get some interesting effects. The glaze, I would think would need to be a bit fluid and be used as a capping over a more stable base glaze. You might test by glazing a piece with a know glaze then making up a wash with rutile and a frit like 3269 or 3110. Do a line test rutile 25 frit 75 and in 10% increments go to 75 rutile/25 frit. Give it a try. Hope this helps Wyndham Thanks for your advise, I'll give it a try. I note you say 3110 which is a high alkaline frit and is commonly used in crackle glazes. If I do a wash with this is it likely to cause crazing of the below glaze? Cheers, Gary
  7. Evening all, I was just wondering, does Rutile promote mottling and streaking or other interesting effects in Earthernware glazes approx. cone 04? Or does this just happen in stoneware. Many thanks.
  8. Thanks for your input. No, there's no glaze chips on the shelf at the end of the firing. I put another kiln load on yesterday, I'll see how this one goes. My normal firing schedule is 3:30 to 500ºc then full power to 1060ºc. The firing normally takes around 9 hours. The firing from last night I had it on a ramp of 4:45 to 500ºc then full power to 1060ºc with a hold of 2min. I increased the first ramp to ensure it was slower whilst any remaining water was pushed out from the glaze incase this was dislodging it. I guess for what you describe you mean slow the top end. On my next firing should I slow it down by an extra hour?, ie something like this: 5:00 to 500ºc then 5:00 1060ºc? I've never used a ramp at the top end, I hope the kiln can cope with it. It seems to go slowly when it gets above about 900. I don't want it to suddenly switch off with an error that it can't heat fast enough. I guess I'll not know until I try.
  9. What kind of soak time would you put in? Would you reduce the final temp to compensate slightly?
  10. This makes me think there may be something soluble in either the slip or glaze that is coming to the surface. Maybe try a different water supply with a small batch, bottled water, etc. Can epsom salts affect anything?
  11. Several questions spring to mind here. How are you glazing? Are you glazing the inside and outside separately and in what order. If so what is the drying time between the inside and the outside? Are you brushing on the glaze? Are you spraying the glaze? I ask these questions as it seems to me that you may have a problem with crawling (glaze pulling away from the surface during the firing). I have experienced this when dipping glazes on thinly constructed work. The bisque becomes saturated when more glaze has been added to a surface. Bubbles or blisters appear on the unfired glaze during drying. These can be smoothed back by rubbing. However in the majority of cases the glaze crawls during the firing because of the lack of adhesion of the glaze to the surface. With brush on glazes this can also occur when subsequent layers can lift off the first layer be it ever so slightly. With sprayed glazes this can also happen when too thick a layer is applied in one hit rather than several thinner layers. One way or another the bisque can becomes saturated. Saturated areas do not have good adhesion with the glaze. With reference to your statement "about 70% of the problem pots have the problem on the side facing the elements" it may be that the side facing the elements initially heats up at a more rapid rate than the rest of the pot and trapped moisture causes further problems with poor glaze adhesion. I note also that your bisque temperature is higher than your glaze temperature. Could this be contributing to the poor adhesion? Regards Johanna Thanks for your reply. Some good things for me to test out here. At the moment I'm dipping them in one. Do you think adding a small amount of medium to the glaze will help adhesion. I'm going to try dip the outside then pour the inside to see if that fixes things (letting them dry between). With regards to firing schedules, I was taught to bisque higher than glaze for earthenware to make sure the impurities and carbon is all burnt out and more won't come out at the lower glaze temp. I wonder if there is still water in the bisque after glazing despite leaving it a day or two to dry. Perhaps I should slow down the initial ramp of the glaze fire; I suppose this could explain why it mostly happens next to the elements because this is where it's getting hot first and is where the water is coming out and dislodging the glaze?
  12. Thanks for your reply. I use the same kiln for bisque and glaze (obviously separate firings). I don't think the bisque is getting too hot, as it's only 15ºc more than the glaze firing. I haven't tested it, perhaps I should get some cones. I'm getting a new kiln in the next couple of months anyway.
  13. I add the sodium silicate in stages over a few days to get the correct consistency, mix with a drill mixer and then let it sit before putting it through a sieve, it's then usually the next day when I use it. I stir it up every time I use it and put it through a larger sieve (a kitchen one) into my pouring jug just in case there are any lumps. I can't imagine there is a layer of sodium on the mould because it does it even on new ones. The surface where the glaze crawls isn't powdery, it's slightly shiny, kind of like a very very very thin layer of transparent glaze.
  14. Thanks for your reply. The clay isn't recycled no, pretty much straight out of the bag, dried, and ground up and mixed with water and sodium silicate to deflocculate, sieved and into a mould. It's by Valentine Clays. I have noticed that about 70% of the problem pots have the problem on the side facing the elements, could there be a problem with some kind of over-firing?
  15. This is why I changed to a glaze I mix up from a recipe and I'm still getting the problem. It makes no sense at all.
  16. I never used to until I got this issue. Since then I have used gloves every step of the way but it doesn't seem to change anything.
  17. I should note also, the insides of the cups come out perfect. It's just the outsides where the problem is occurring.
  18. Hi everyone, I have a problem which is driving me absolutely insane. This problem has only just started popping up in the last few months. I am using earthenware clay and earthenware glazes, but the glaze just doesn't take correctly on 60% of the pieces. I am using a comercial claybody I have tried with a commercial white glaze and a glaze from a recipe and both give the same effect. For this particular project I am using the clay to make casting slip (Which I have done in the past without issue). I have been using this clay and glaze for years and never had a problem. I'm not doing anything different at all. I bisque to 1075ºc and glaze to 1060ºc I wash each piece of bisque to ensure dust/dirtfree surface before glazing, allowing it to dry for a few days in a warm spot. I also use surgical gloves to ensure I don't get finger grease on the pots before glazing. I attach a photo of what's happening. Any help would be much appreciated. Thanks.
  19. You may as well keep them. Even if you need the space, just dry them out and bag them up and keep them for a later date. They shouldn't take up that much space as dry powders. Or like others have suggested create a waste bucket and you might get some nice effects.
  20. Useful to know. But, how do you know if it is deflocculated or if it has too much water in it?
  21. Hi everyone, I have been using a glaze from the following recipe (from the book 'Colour In Glazes' by Linda Bloomfield): 39 Calcium Borate Frit 27 Soda Feldspar 5 Whiting 6 China Clay 23 Quartz _____ 100 _____ I expected this glaze to be a little more transparent and a little glossier. It is slightly under-fired, it's a cone 04 glaze and I fired it to 1050ºc by accident, I believe it should be around 1060º-1070ºc. Can this amount of under-fire cause the glaze to be not as transparent and have a satin finish instead of gloss? I also tried adding 0.5% Cobalt and it turned out a matt/satin opaque blue. I have used 0.5% Cobalt in a transparent glaze before and it came out perfectly, semi transparent and glossy. Other than the problems listed above the glaze works quite well, doesn't run, and fits my clay body well unlike most of the transparent glazes (commercial) I have tried. My questions are: - Can 10-20ºc underfire cause these issues? - If I re-fire to the correct temperature will it give better results? - If I fire new pieces to the correct temperature will it be better? Thanks for any advise you can give. Gary
  22. Hi everyone, I once read somewhere than when you are double dipping you can paint on a chemical between each layer to allow the different glazes to mix better. Does anyone know what it is? Im using 04 glazes. Thanks
  23. Thanks for your suggestions everyone. I will give them a go over the weekend. I can make this glaze cheaper than the commercial clear I use. I also love to experiment. I think it's a nicer feeling to know you have made something rather than just buying it, that's too easy.
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