andros Posted January 22, 2021 Report Share Posted January 22, 2021 Hello! I’ve recently made my first raku firings in my home made raku kiln (a readapted tiny electric kiln) but I’ve had pretty bad results… I tried 4-5 firings using different commercial glazes thought for “normal” electric kiln low firing: colored glazes thought for 980-1050°C\1800-1920°F (with some addition of 850-1000°C\1560-1830°F Alkaline frit for lower a little bit the melting pont and make them more translucent), metallic glazes and “pearl effect” colored glazes (i.e. with addition of bismuth nitrate, I guess) that have by themselves the right temperature range (900-950°C\1650-1740°F, I believe…). The metallic glazes went out fairly well, but for the others it have been a disaster... the “pearl effect” glazes came out complitely black, very black, and very matt. The colored glazes came out full of bubbles and with a very strange metallic colored surface; this metallic layer could be removed by scratching with a steel wool. Unfortunately I’ve not taken pictures… This was the very first time for me, and I have not previous experience, no courses, never seen other peole do this kind of firing, so now I can only guess what went wrong. The first observation is that the firing time have been quite shorter that expected: 5 min at the maximum to see a “wet” glazed surface. My kiln is very very small (a cube with 13” sides), but this looks to me a very short time… So the causes for the disaster, I guess, are primarily due to the fact that I made the firings in reduction condition, too much gas, too few oxigen. This even if the fire didn’t look “smoky”. This could explain the black and metallic surfaces (even if I can’t figure out the real specific cause of the metallic surface). For the bubbles I don’t know if I waited too little time by the moment in which I’ve seen the “wet” suface, or if the temperature rose too fast, or it was too high. Could somone give me some idea about what have been my errors? Link to comment Share on other sites More sharing options...
Sorcery Posted January 22, 2021 Report Share Posted January 22, 2021 Seems a little fast. What Clay? It could be gassing off making the bubbles. Could be the "normal" glazes too. Sounds fun Anyway! Sorce Link to comment Share on other sites More sharing options...
andros Posted January 22, 2021 Author Report Share Posted January 22, 2021 I used a so said "Semi-refractory" earthenware clay with 0-0.5 mm chamotte at 40% containing molochite. Bisque firing range 980-1150°C. I guess that it would be not useful to mention the brand name, since it's an italian brand. For "normal" glazes I mean commercial low firing glazes, not "raku glazes". Link to comment Share on other sites More sharing options...
PeterH Posted January 22, 2021 Report Share Posted January 22, 2021 7 minutes ago, andros said: I used a so said "Semi-refractory" earthenware clay with 0-0.5 mm chamotte at 40% containing molochite. Bisque firing range 980-1150°C. I guess that it would be not useful to mention the brand name, since it's an italian brand. For "normal" glazes I mean commercial low firing glazes, not "raku glazes". What cone/temperature did you bisque at, how long did it take? Link to comment Share on other sites More sharing options...
andros Posted January 22, 2021 Author Report Share Posted January 22, 2021 980°C. I can't tell about the timing. I don't have an electric kiln, so I must rely on a shop that fire my stuff for me. I don't know the details of firing program but it's a standard one for earthenware... Link to comment Share on other sites More sharing options...
PeterH Posted January 22, 2021 Report Share Posted January 22, 2021 28 minutes ago, andros said: 980°C. I can't tell about the timing. I don't have an electric kiln, so I must rely on a shop that fire my stuff for me. I don't know the details of firing program but it's a standard one for earthenware... Great, I was just checking that it wasn't an iffy bisque in your raku kiln. Link to comment Share on other sites More sharing options...
JohnnyK Posted January 22, 2021 Report Share Posted January 22, 2021 What is your process after you reach the "wet" glaze stage? How do you reduce your pots? Some of your problems may be the use of so-called "regular" glazes instead of Raku glazes... Link to comment Share on other sites More sharing options...
andros Posted January 22, 2021 Author Report Share Posted January 22, 2021 As soon as I saw that the glazed surface was "wet" I've turned off the gas, than opened the kiln and passed them in a bucket with pine sawdust as fast as possible, and I've closed it with the lid. I've left them in reduction for 10 min. More or less... Anyway I don't think that the problem is the reduction. While moving my stuff in the bucket I already saw that the “pearl effect” glazes came out complitely black and that the colored glazes came out full of bubbles and with a very strange metallic colored surface. So it happened inside the kiln, during firing. Link to comment Share on other sites More sharing options...
oldlady Posted January 22, 2021 Report Share Posted January 22, 2021 not my area of expertise but i have learned from many joint firings. the time is much too short, the bubbling of the glaze says so. i have known a very successful potter who for many years used low-fire (cone06) colorful glazes to enhance her raku work. they do a great job, they were designed to go to cone 06 which is about the temperature her raku firings reached. she did have a pyrometer to let her know that the temperature she wanted had been reached. look up Marcia Jestaedt. look at the fans and robes. Link to comment Share on other sites More sharing options...
andros Posted January 22, 2021 Author Report Share Posted January 22, 2021 Thank you oldlady! Link to comment Share on other sites More sharing options...
JohnnyK Posted January 22, 2021 Report Share Posted January 22, 2021 45 minutes ago, andros said: As soon as I saw that the glazed surface was "wet" I've turned off the gas, than opened the kiln and passed them in a bucket with pine sawdust as fast as possible, and I've closed it with the lid. You might try using shredded newspaper in your reduction bucket instead of the sawdust, you'll get a better burn there. Also, slow the original firing...20-30 minutes should work a lot better... Link to comment Share on other sites More sharing options...
Babs Posted January 22, 2021 Report Share Posted January 22, 2021 Think memgee Marcia Selsor coukd help. Pm her. Benzine also has experience in thisfield Link to comment Share on other sites More sharing options...
andros Posted January 25, 2021 Author Report Share Posted January 25, 2021 On 1/22/2021 at 5:56 PM, JohnnyK said: You might try using shredded newspaper in your reduction bucket instead of the sawdust, you'll get a better burn there. Also, slow the original firing...20-30 minutes should work a lot better... Tahk you Johnny. Anyway I think that the problem is that the firing has been too fast. I was concerned because at the shop I asked for a canister of propane (because I heard that it has a better calorific value) but reading the canister tag once at home I noticed it was LNG, so I opened at the maximum the canister (and torch) valve, but evidently my kiln is so small that even the LNG was not only enough, but I have to be careful not to overdo it .. Link to comment Share on other sites More sharing options...
Bill Kielb Posted January 25, 2021 Report Share Posted January 25, 2021 9 hours ago, andros said: that even the LNG was not only enough, but I have to be careful not to overdo it .. Propane has a bit more than double the heat of natural gas. Having said that, kiln burners are reassure operated, meaning start out slow, small flame and heat slowly. Turn up gradually as needed. If you have a pyrometer this is easy so that may help. I think you will find your glazes melt between approx. 1600f and 1800f. 20 minutes is plenty fast. As far as surface reduction, glazes are formulated for it. Only a few metals react to reduction and if the glaze is not made for it then little to no reaction. As far as reducing medium, if I want very clean reduced surfaces I would place newspaper neatly around the inside of the bucket and set my piece right in the middle not touching anything. Paper burns, lots of carbon monoxide produced as the fire smothers, lots of surface reduction. Newspaper works really well. If you like the variance and carbon associated with stuff in contact with the pot, pieces of newspaper are just fine. I have a friend that tours the schools and he sets his pieces inside a paper bag inside the bucket and covers. Easy, super results without a bunch of shredded mess. Link to comment Share on other sites More sharing options...
Benzine Posted January 26, 2021 Report Share Posted January 26, 2021 On 1/22/2021 at 3:57 PM, Babs said: Think memgee Marcia Selsor coukd help. Pm her. Benzine also has experience in thisfield I know a thing or two. Marcia is definitely the expert. I've tried a lot of different reduction materials over the years; newspaper, shredded paper, cardboard, dried leaves, dried corn husks, saw shavings (from a table saw/ planer) saw dust (from a sander), and a dried pumpkin *cough*... I've found newspaper to be quite reliable, and less likely to mar the surface like saw dust or other thicker combustibles will. I like to have a layer of saw dust/ shavings on the bottom, both for a bit of padding on the metal bin, and to give a bit of constant reduction, while more is being unloaded from the kiln. The newspaper just burns too fast on its own. So basically I use a combination of the saw dust and newspaper. It's worked well for me the past couple years. Fun little tidbit, I had a student with a couple pet snakes, who wanted to try their shed skins for reduction on her project. It goes up faster than nearly anything I've ever used, and makes a pretty bad smell... I had issues with bubbly surfaces on the first load I did with my students. It was a combination of not waiting long enough before unloading, and not have my opening quite wide enough. I expanded the in and out takes by an inch, which allowed more oxygen in and better combustion, and that helped *A LOT*. I've never really had an issue with the colors not coming out, other than just the variations you get with Raku normally. Link to comment Share on other sites More sharing options...
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