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  1. Thank you, Mark C. And Ray for your kind advice. I am sorry to have been so long to reply but I have been away this month without access to my computer. Mark, I use the glaze I described which is clear (cone 10). I add mason stain of different blue and green shades (1%) to give it color in oxidation and copper and iron in reduction. It crawls along thin edges. This seems worse in oxidation firing. Ray, I will definitely try to add more flux. Thanks for the suggestion. Nielestrick, the porcelain pieces are very thin but carved so the whole piece is dipped at once. I guess i will try to apply the glaze more thickly, so it will not run off the thin parts as much. Thanks for the advice. Happy New Year to you all!
  2. Can you explain this comment? What type of impurities? Are you sure they are from the clay... and not the local studio environment? This is NOT my experience with their clays. I use a small amount of their porcelain along with mainly stoneware. If you are having problems, have you contacted them about it? best, ....................john Hi! Thanks so much for responding to my plea for help. I just wish I had reread my post before I sent it off last night. I did not mean to imply that all of Sheffield's porcelain is dirty! Just my unfortunate batch! Please read the post I wrote to nellestrick, above. As I said, the Sheffield folks have been wonderful and I love their clay. The porcelain is an absolute dream to throw with. They have replaced the problem batch with a new one, free of charge, and I am eager to see how it does in my big reduction firing. When I cut the wet clay with my wire I do not see the clumps of brown stuff that the other one had running through it. My problem is that I made a lot of pottery with the old batch and I am trying to make the best of the situation. I also would like to find a use for the old batch. I guess I will just switch to the celadon glaze that I use in reduction, but leave out the iron and copper. Also, I will try to dry the pots after they are lined with glaze. Sharon
  3. Thanks so much for your response. My glaze is a clear glaze. I sometimes add mason color to it to give the ware a blue or blue green tint. I don't have much crawling at cone ten in reduction, either,but then again I have not used this clear glaze much in reduction conditions. I always use celadons and these behave very well on Sheffield cone ten porcelain.
  4. I adore the clays from Sheffield pottery, especially their white stoneware. I have been using it for years. I have only bought one batch of their porceIain, as I am relatively new to the medium. I misspoke when I said their porcelain has impurities. Most likely it is just that one batch. When I brought the problem to Sheffield, they were marvelous as always and replaced my porcelain batch, free of charge, with a new batch that is clean in reduction. The old batch was bought 5 years ago and had what looked to be clumps of iron oxide dispersed though out the clay. When fired in reduction these left large black metallic blisters on the clay. My first cuts into one of the new bags look good. Since Sheffield did not want my leftovers of the old batch and I have a large body of work made with the contaminated batch, I am trying to find a use for this porcelain. I hope to avoid the black spots by firing in oxidation (they still show but are much lighter, also I wire cut each bag into sheets and hand pick out the powdery chunks of contaminant). Thanks so much for the advice about glazing the inside first. I will try that!
  5. Hi Folks, I have started to use cone 10 porcelain from sheffield pottery. Since it is full of impurities, I decided to fire my porcelain pots in oxidation. My pieces are pretty thin and I get crawling just along the rim of each piece....like clockwork. Crawling is also a problem along sharp ridges where curves of the form jut out and then recede. Does anyone use Sheffield's porcelain cone 10? If so, would you be kind enough to share a clear porcelain glaze recipe that does not crawl, with me? FYI, I wear gloves to handle the ware, glaze immediately after bisque so dust and grease are not a problem. I have added 1.5% bentonite to my glaze to add some small platelets to my glaze mix which has made little to no difference. The recipe which I use (from Mary Risley (RIP) at Wesleyan University 40 years ago....): Custer spar 33 Flint (silcosil) 32 Whiting (snocal 40) 20 Grolleg Kaolin 15 Help?!!! Does anyone have any recommendations (bedsides switching to EPK in the glaze. I am in the process of testing it)? Sharon Nahill Oak Hill Pottery Meredith, NH
  6. Hi folks, I was wondering if anyone could recommend a good spray gun. I have a general purpose one but it only has fan shaped spray.
  7. Thanks so much for all this help. You are a godsend. In answer to your questions...I do not get carbon coring with the firing schedule that I use as i bisque very slowly. My problem is that i only get beautiful blues on occasion with the same glaze. I will definitely try your suggestion to separate the reds from the blues and a do a lighter reduction. Maybe that is the explanation....when the reduction is heavy i just dont get blue but when the reduction happens to be light by chance of location in the kiln....the blue shines. Could i bother you to suggest a rutile recipe that is most likely to work? Which of those listed by jb do you think I should start these experiments with? I will also make some porcelain test tiles to get to the bottom of all this..... I unloaded a kiln today in which I tested light vs dark rutile + or - titanium in durhams blue rutile glaze (yellow iron oxide) . You were right. My 30 year old batch of dark rutile came out very similar to my new light rutile....kind of indistinguishable. Interestingly, the type of iron oxide made a huge difference. Red was awful muddy brown while the yellow made the rutile just glow a brilliant midnight blue. I will update you as to my progress, Again, thank you for your generosity, Sharon
  8. Thanks for your rapid response. Both rutile glazes are in john britts book in his chart on rutile blue recipes. Most of them are not "blue" for me, although Rays rutile can be a gorgeous blue purple. By the way...I have a Bailey Kiln...18 cubic feet..2 years old. I love it but what do I know? Be well, Sharon [qute name=Mark C.' date='30 August 2012 - 05:38 PM' timestamp='1346366284' post='21555] My experience is my reds like more reduction than most other glazes and that especially true in the early stages as well. I never add barium glazes to my standard reduction loads. To me it sounds like you really are doing a heavy long reduction-my bottom spy plug never has a flame lick to it My Barium glazes are fired cooler and with a lot less reduction than say reds My rutile glaze like reduction and long soak times near cone end points -this helps lay down the surface if its bubbling. What is Rays name so I can view these glazes. I'll look up Johns rutile 11 in his book and see what it looks like Mark
  9. Dear Mark, Thanks for your help. In answer to your questions...i use white stoneware with grog from Sheffield Clay Co in MA. I fire with a strong reduction atmosphere (500-600) starting at around 1560 degrees farenheight all the way through untill my kiln reaches cone 10. I end up with a considerable soak from cone 9 to 10 as the temperature climb under reducing conditions in my kiln is very slow. This works out wonderfully for my reds... I do see a nice flame jet from my bottom spy hole. It is about 6 inches long. I wonder if I am just using the wrong glazes? Perhaps I should try firing my reds at a different time than my rutile and barium blues, for that matter. I use john britts rutile 11 and rays rutile taken from his book which is available free on line....I swear....that guy is a saint! Do you have any glaze recommendations? I will certainly try less reduction.... Be well and thanks so much for your help, Sharon
  10. My rutile in 4 decades has always changed color at various times with little change in my final glaze results. I always buy 50 # bags. Their have been several large color swings in past few years. Let us know if you find any final color differences-I have not . Weld Rod Titanate one of the larger companies has been bought out and the color changed when that happened (I have a bag of that now as well as another company) one is light one is dark. Back to rutile woes -I'm not up on Johns firing schedule if you want to post it great if not I will add that more reduction early can cause pitting and well as what clay body its on. What clays are you using? stoneware is more problematic than porcelain . I used stoneware for over 15 years with very mixed results due to pitting and when I went to all porcelain it really helped. Pitting still occurs but rarely now. Clean bisque ware is key as well as glaze thickness (not to thick). I do not use cones in bisque anymore (past 15 years or more-just my digital meter and eyeball but make sure your not underfiring bisqueware. I measure my glaze water content with a hydrometer (1520) and use an oxygen probe for reduction repeatability.My new meter reads upper 30s to low 40s If you are firing seat of the pants reduction is the lower spy plug have flames or not? If you are using any of these things what are the numbers?? Hope some of this helps Mark
  11. Thanks for the quick response. I fire to cone 10 reduction. Following John Britts firing schedule...I would say that I fire moderate to heavy reduction. I have mixed light and dark rutile as i had bags of each from long ago. I am testing that mix against light rutile that I got from Bailey.
  12. Oakhillstudio I have very mixed results with rutile glazes. Sometimes they come out spectacularly and sometimes they are a dull tan with bubbles erupting from the surface. Could anyone make a recommendation as to source and firing schedule? Also...any guidance on how to elimliminate blisters would be greatly appreciated! FYI...I have read every entry on the web that I can find.
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