nbsa Posted January 27, 2022 Report Share Posted January 27, 2022 A mug I painted with four coats of Mayco Fundamentals underglaze appeared burned out after firing, photos attached. At first, I thought perhaps I didn't do enough coats of underglaze, but the other side of the mug looks perfectly as expected. The clay body is trail mix cinnamon from Georgie's Ceramic & Clay Co. in Portland. I fire in a community studio which handles firing for us and they fire at cone 6. Is this fault something I could have controlled, or could it have been a result of how the kiln was arranged & fired? Link to comment Share on other sites More sharing options...
Bill Kielb Posted January 27, 2022 Report Share Posted January 27, 2022 It does look like another glaze flashed over onto your mug, unfortunately that’s hard to predict or control in a community kiln firing situation. What is interesting is your overglaze does not appear particularly melted.. It might just be the pictures, but I always worry when heavy applications of underglaze are applied that the overglaze is capable of melting fully over it. Some underglaze colors are more difficult than others. Just an aside, many find fairly sharp corners on handles to be uncomfortable when used for a period of time. Unless artistic, we usually suggest smoother is usually more comfortable for most. Nice mug, nice design! Link to comment Share on other sites More sharing options...
Mark C. Posted January 27, 2022 Report Share Posted January 27, 2022 Flashed off another nearby pot. Who ever loaded it did not know this maight happen is my guess.I rather like flashed pots myself more random Link to comment Share on other sites More sharing options...
Callie Beller Diesel Posted January 27, 2022 Report Share Posted January 27, 2022 It’s not a flaw in a functional sense, although industry would consider it an aesthetic one. Sit with it for a few days or a week before you decide if YOU think it’s an aesthetic flaw, or if it’s part of the things that make handmade pottery interesting. Link to comment Share on other sites More sharing options...
Hulk Posted January 27, 2022 Report Share Posted January 27, 2022 From the bottom up, white, blue, brown - is the brown unglazed clay or clear glaze? Just curious. I've had some of what had to be flashing (particularly, from chrome/tin red to blue), however, also have seen where a pot is in the hotter part of the kiln (middle shelf) and the thinner section of the wall facing the elements is differently colored, where it got a bit hot, I'm guessing. Perhaps your pot got a bit hotter on the smudged side; note the edges of the blue in the discolored area didn't get the brown smudge - where the underglaze is thicker? Any road, I (also) like the look! The blue, particularly on the "other" side has some white showing through, which echoes the brown, imo. Link to comment Share on other sites More sharing options...
nbsa Posted January 31, 2022 Author Report Share Posted January 31, 2022 On 1/26/2022 at 10:55 PM, Bill Kielb said: It does look like another glaze flashed over onto your mug, unfortunately that’s hard to predict or control in a community kiln firing situation. What is interesting is your overglaze does not appear particularly melted.. It might just be the pictures, but I always worry when heavy applications of underglaze are applied that the overglaze is capable of melting fully over it. Some underglaze colors are more difficult than others. Just an aside, many find fairly sharp corners on handles to be uncomfortable when used for a period of time. Unless artistic, we usually suggest smoother is usually more comfortable for most. Nice mug, nice design! Ah, I forgot to mention there is no overglaze, just using underglaze here. The interior is lined with a clear glaze, though. Its a little hard to tell from the photo, but the burned out side almost has a "glossy" like appearance, which probably makes the other side appear like it hasn't fired completely. Fortunately this is all experimentation for me, so I'm not too bothered! Link to comment Share on other sites More sharing options...
nbsa Posted January 31, 2022 Author Report Share Posted January 31, 2022 On 1/27/2022 at 8:30 AM, Hulk said: From the bottom up, white, blue, brown - is the brown unglazed clay or clear glaze? Just curious. I've had some of what had to be flashing (particularly, from chrome/tin red to blue), however, also have seen where a pot is in the hotter part of the kiln (middle shelf) and the thinner section of the wall facing the elements is differently colored, where it got a bit hot, I'm guessing. Perhaps your pot got a bit hotter on the smudged side; note the edges of the blue in the discolored area didn't get the brown smudge - where the underglaze is thicker? Any road, I (also) like the look! The blue, particularly on the "other" side has some white showing through, which echoes the brown, imo. The bottom is Mayco Fundamentals sage green underglaze, the middle is Mayco Fundamentals Grey, and the upper part is just the draw clay body. I did four coats of each. There's no glaze on top (though there is a liner glaze on the inside). I wish I could have known where it was placed in the kiln! I suppose I can ask them, as I wonder if others experienced the same thing. Link to comment Share on other sites More sharing options...
oldlady Posted January 31, 2022 Report Share Posted January 31, 2022 oooh,,,,,,, raw clay on the lip of a mug is uncomfortable for many people. if you decide to make these for use, my suggestion is to run the interior glaze over the lip and down at least a half inch. wish there were more light on the front of the mug. Link to comment Share on other sites More sharing options...
Min Posted January 31, 2022 Report Share Posted January 31, 2022 As the smudging is the same colour as the claybody it looks like some of the claybody got rubbed against the underglaze prior to firing. Something that can happen when just using a liner glaze with no glaze on the outside is dunting. Unless the glaze fits the clay really well the mug can crack when filled with hot liquids, sometimes quite dramatically. The thinner the pot and the thicker the glaze the greater chance of dunting with an ill fitting glaze. If you are going to glaze the inside only it's a really good idea to check for dunting. To stress test a clay for glaze fit in regards to dunting put a few mugs in the freezer overnight then place the mugs in the sink and immediately pour boiling water into them. I know nobody would ever do this type of thing in the actual usage of the mugs but what it's doing is stressing the mugs to see if there is a good fit between the glaze and the mug. One other thing, the clay you are using has a posted absorption of 2.73%. It would be a good idea to check the absorption yourself as this is a bit high for functional pots used for liquids. If the absorption is too high the pots can leak, regardless of whether they are glazed inside or not. Other issue with an absorption too high is staining / discolouration from usage. Probably won't show on the red clay though but something to be aware of if you use a lighter body that isn't a low absorption clay. Link to comment Share on other sites More sharing options...
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