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Celia UK

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Everything posted by Celia UK

  1. I am a great fan of Jennifer McCurdy. Having found her on the Internet and watching the only 2 videos of her working, I contacted her and visited her last Autumn on a trip to the US from England. Like many potters I've met she was warm, welcoming and very generous, giving her precious time (she was preparing for an upcoming show), showing me her studio and telling me about her work. I just love her pieces and am totally in awe of her skill - more and more so, as I make feeble attempts at using some of her techniques. If you like porcelain and want to see someone working it with amazing skill and precision, take a look at Jen on youtube.com. Awesome!
  2. I started with the 'single cream' thickness in mind, but this was generally too thick for my glazes, so I now think 'milk'. It could be that single cream thickness is different in UK. Also, yoghurt comes in so many thicknesses, that this really doesn't help at all. Test, test, test ....as everyone keeps saying. No short cuts here.
  3. Thank you for your comments and some things to try. Celia
  4. I recently used cobalt carbonate to fill a stamped motif on two small pieces made with white earthenware. I applied it when they were bone dry and cleaned up carefully (I thought) before bisquing in my electric kiln. There was cobalt residue on both pots which only showed after bisquing - very messy! I know I could have had SOME on my fingers, but the cobalt appears to have spread during the firing. There was also some blue on another pot that was placed nearby in the kiln. I was able to clean them up, but it took some time! Any ideas as to how / why this happens and suggestions for preventing it another time. Thanks.
  5. Having read all of the above, it's making me worry about my clay / glaze now. I am using smooth white earthenware - and mostly make decorative pieces. However, if I want to make some mugs, what would be the best bisque firing temperature and same for glaze fire. I generally use a mid range transparent glaze, coloured with small qty of oxide. (Copper carbonate, cobalt carbonate, red/black iron oxide,)Are these 'safe'? All advice greatly welcomed. Celia
  6. No. News to me in the UK. Sounds like a hoax. If so, bad taste.
  7. Rediscovering the joys of clay

  8. Ah yes, that may be a bit trickier to control since you would not be able to isolate a single component of the prepared powder, but it couldn't hurt to do a few 100gram test batches with different concentrations (say .5%, 1%, and 3%) of a frit that contains borate added to your glaze powder. It is a good thing that you get the glaze in powdered form, because if it were premixed with water then it would be much harder to consistently add the same amount of frit to each glaze batch (if the testing turns out). I have definitely found that crazing will happen when there is too thick of a glaze application. Using just clear glaze really doesn't take much to make a nice glossy seal. If you take a credit card and scrape a line in the glaze you should see that the thickness on the piece is about the width of credit card or even a touch less (you can then rub your finger back over the scrape to fill the glaze back in). Also, if you thin it down it would definitely help glazing the piercings. (I too am very much into pierced designs) I find if the hole has filled in as I pull the piece up from the dip, if I blow gently into the opening it will break the surface tension and possibly clear it. Otherwise if it stays closed, depending on the shape, i can use a small drill bit to hand "drill" the hole out without completely chipping away the dried glaze. You can take your finger and gently rub over the runs to "sand" them away so to speak, or you can use actual sand paper to gently grind them down. Just make sure to try to keep the dust down (wear a mask). I was taught that when you stick your hand in the glaze and pull it out there should only be a thin layer still stuck to your fingers, if it's thick and sticks like gravy to the back of a spoon it's too thick. There is also a way to make a density meter with a block of wood and a weight so that you know the glaze is the same thickness every time you make it. Basically you attach the weight to the end of the stick and place it in a bucket of plain water so that part of the stick is floating above the surface. Mark where the water level is on the stick. Next, place it in the bucket of well mixed glaze that you know has been combined with the right amount of water (you've tested how well it covers the bisque and possibly fired to see if it crazes) and mark where the glaze level falls on the stick (it should be lower than the water mark). Then, the next time you mix that glaze you can drop the stick in the bucket in between intervals of adding water to the powder until the stick comes to rest at the glaze level line. You should end up having the same density glaze every time. As with nearly everything, this was not my original idea. I believe I got it out of a Ceramics Monthly magazine actually. As far as firing the bisque to a higher temp then glaze firing, I've honestly never done so since I fire to cone 9/10 and the clay would never accept the glaze at that point since it would be completely vitrified. But I am curious if it helps with crazing at lower temps since it is much more economically feasible to fire lower. Best Shannon Hi Shannon - thanks again! I've also read about dipping your hand in to test the glaze thickness, but I've found ideas of 'thin cream, thick cream, gravy, breaking over knuckles' etc a bit on the subjective side and dependent on my cookery knowledge / skills ! I did look at a hydrometer in the homeware store recently - having read that this was the 'proper' way to measure viscosity. I resisted buying one, but as it was less than £5 I may invest - though your idea sounds very clever too! Whatever, I need to identify the ideal measure first!!! Testing, testing.... Have a wonderful Christmastime. Celia
  9. Ah yes, that may be a bit trickier to control since you would not be able to isolate a single component of the prepared powder, but it couldn't hurt to do a few 100gram test batches with different concentrations (say .5%, 1%, and 3%) of a frit that contains borate added to your glaze powder. It is a good thing that you get the glaze in powdered form, because if it were premixed with water then it would be much harder to consistently add the same amount of frit to each glaze batch (if the testing turns out). I have definitely found that crazing will happen when there is too thick of a glaze application. Using just clear glaze really doesn't take much to make a nice glossy seal. If you take a credit card and scrape a line in the glaze you should see that the thickness on the piece is about the width of credit card or even a touch less (you can then rub your finger back over the scrape to fill the glaze back in). Also, if you thin it down it would definitely help glazing the piercings. (I too am very much into pierced designs) I find if the hole has filled in as I pull the piece up from the dip, if I blow gently into the opening it will break the surface tension and possibly clear it. Otherwise if it stays closed, depending on the shape, i can use a small drill bit to hand "drill" the hole out without completely chipping away the dried glaze. You can take your finger and gently rub over the runs to "sand" them away so to speak, or you can use actual sand paper to gently grind them down. Just make sure to try to keep the dust down (wear a mask). I was taught that when you stick your hand in the glaze and pull it out there should only be a thin layer still stuck to your fingers, if it's thick and sticks like gravy to the back of a spoon it's too thick. There is also a way to make a density meter with a block of wood and a weight so that you know the glaze is the same thickness every time you make it. Basically you attach the weight to the end of the stick and place it in a bucket of plain water so that part of the stick is floating above the surface. Mark where the water level is on the stick. Next, place it in the bucket of well mixed glaze that you know has been combined with the right amount of water (you've tested how well it covers the bisque and possibly fired to see if it crazes) and mark where the glaze level falls on the stick (it should be lower than the water mark). Then, the next time you mix that glaze you can drop the stick in the bucket in between intervals of adding water to the powder until the stick comes to rest at the glaze level line. You should end up having the same density glaze every time. As with nearly everything, this was not my original idea. I believe I got it out of a Ceramics Monthly magazine actually. As far as firing the bisque to a higher temp then glaze firing, I've honestly never done so since I fire to cone 9/10 and the clay would never accept the glaze at that point since it would be completely vitrified. But I am curious if it helps with crazing at lower temps since it is much more economically feasible to fire lower. Best Shannon
  10. Thanks John - a very clear explanation and some specific things or me to work on. I can see some disciplined testing coming on in the New Year to reduce all the guesswork. The reason I'm going to these lengths, is so as not to waste two 5kg bags of glaze powder that I found at the back of the art store at the school where I used to be the headteacher (recently retired hence new interest in ceramics). I could just dump them and start over, but that seems wasteful & I could have the same problems with another glaze. Anyhow, it's a good exercise to go through and will be increasing my knowledge along the way. I need to be philosophical about ending up with unsuccessful test pieces and using up my clay stock, but I can also look on it as throwing practice, if I use small bowls rather than test tiles! I SHOULD be wrapping Xmas presents and doing the last food shop today, but I'm going to source the boric oxide and SiO2 (need to look this up!) online first! Thank you so much for taking the time to reply - what a great way to get help, I love it! Hope you have an enjoyable Christmastime. Celia
  11. Thanks Shannon - though I think I misled you by saying I mixed my glaze from powder, as this is a prepared glaze powder from my supplier, rather than me mixing up from a recipe (too many ingredients to buy at this stage). Do you think I could still try adding the ferro frit? I'll have a look in my supplier's catalogue to see if it's available. Latest firing was more successful. A few more things to learn from it - mostly in respect of my glazing technique. I need to improve my dipping skills and use of glaze tongs. Also as much of my work has holes pierced or incised there has to be a good way of getting an even glaze - with dipping, the glaze pours through the holes and it's hard not to get drips and runs. Do you think thinning the glaze somewhat would help? Alternatively, as I wondered in my previous post, perhaps bisquing at a higher temperature, making the clay less porous, would help. Oh the joys and frustrations....... Celia
  12. I know it may seem very straight forward, but since you say you mix your glazes from powder, are you using the same Kaolin (clay component) that your clay body is made from? Often times there are very subtle differences in the clay that is pulled from one location and the clay from another location that can actually affect fit. I've always made sure that even if a glaze recipe calls for a different kaolin to still use the same kaolin that is in my clay for fit issues. So far, cross my fingers, I have not had any colorant issues from doing so. I also have had issues with bubbles & crazing in my clear glazes and have found a wonderful resource in The Potter's Dictionary by Frank and Janet Hamer. It is a comprehensive resource for almost all things clay. Including what goes wrong, and possible ways to fix it. I found that adding a bit of frit which contains borax can really help improve the clarity and fit of the glaze. The frit I used is ferro frit 3195, a high calcium borate frit from my local supplier, in a concentration of 2-5% in the glaze. Obviously, more testing will need to be involved to determine what will work with your specific resources and environment. I use a numbering system on my test tiles and use that to test one variable at a time (the only thing being hard to test specifically is the firing schedule/temp). That way I can cover a bunch of different variables in one kiln firing and adjust based on the out come. I hope this helps as one emerging artist to another. Shannon EW Schanus
  13. Thanks Marcia. Think I need to narrow down my testing to reduce the variables. Once I have a new batch I think I'll do some systematic test fires and just change 1 variable at a time - as a former teacher, I should know that that's good scientific investigative practice! It's only the cost factor of firing the kiln that stops me doing this - want to get on with making final pieces! I guess this is a case of more haste, less speed and time taken at this stage will pay dividends in the long run. As generally i only want a thin glaze then bisquing higher would help with that I believe, by making the clay less porous? I am in the UK - well spotted! It always surprises me that the US hasn't ever gone metric - I thought we were the dinosaurs! I have just joined a local Potter's Group, so I will be able to pick other members' brains there too, in the new year. In the meantime I'll keep my fingers crossed until I open the latest glaze firing, in the morning.
  14. I am fairly new to ceramics, very new to firing my own work. Have small 40 litre electric kiln - make small thrown pieces. I mostly use smooth white earthenware and clear glaze with oxides added or over underglaze colours. I have fired various clays at the same time e.g. St Thomas white, and different White Earthenwares, I mix the glaze from powder and sometimes add oxides. I DO record details of all firings but the outcomes have been so inconsistent I haven't been able to identify a) ideal bisque firing temp and glaze firing temp. Some pieces made of same clay body and with same glaze, are not equally successful. I have had 'pinging' problem with glaze cracking up to a week after firing on some pieces, (I understand this is a glaze fit issue), but I don't understand why this happens on some pots and not others? Everything is always bone dry before bisque firing and I leave the kiln until it is cool before opening. Have bisqued at 06 and glazed at 05: bisqued at 04 and glazed at 05 (read somewhere to bisque higher was better to ensure nothing nasty came through glaze....but generally others say glaze higher!) Form is more important to me than the decorative effects. I LOVE my unglazed, bisqued, smooth white earthenware, and am exploring subtle oxide additions for some pieces. My best pieces recently, were clear glazed on the inside and unglazed on the outside - no 'pinking' on these pieces, but 2 that were glazed inside and out now have long cracks in the glaze. It's so frustrating when so much work has gone into the pieces - throwing, carving, incising, building on etc. then a successful bisque, all to be lost in the glaze firing! ANY ADVICE/SUGGESTIONS would be most welcome.
  15. I had a similar problem as I had slip made up from throwing water and my trimmings, so I didn't know the original dy weight of the clay. Found a basic recipe online which was 56g (2 ozs) oxide for 1000 ml liquid slip. I've mixed up some test batches, using cobalt carbonate, copper carbonate and manganese dioxide, but haven't fired the tiles yet. Will post again once fired and glazed. For future recipes, I'm going to keep a tub of dry trimmings so that % ages are easy to calculate. Good luck! Celia UK
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