rebs

@Bill Kielb @Min i figured out the shrinking of the photo. it doesn’t look like ‘regular’ pinholes does it?

hello all you helpful people, really grateful for all the help i’ve gotten in here i’m trying my luck again! i’ve had some (new) challenges with ‘regular’ pinholes too. and i can’t seem to figure it out. i’ve made some marbled pieces with a blue and a speckled clay. they are slow bisque fired at cone 05 and slow glaze fired at cone 6. the ones fired in my relatively small kiln just had a few pinholes, and the ones i last fired in my new (old) larger kiln had a lot more pinholes in them. i have some theories about what went wrong after a lot of internet investigation and helpful people and posts in here..: -this was the first time i closed all three peepholes at the side during a glaze fire (and more air flow makes pinholes less likely?) -i’ve read that flat pieces is more likely to get pinholes, as to curvy stuff as for example bowls? -larger kiln vs smaller kiln and different cooling can give different results? (but in my case then it should be the other way around..?) on top of this i heard a podcast episode of: ‘for flux sake’ (which i found a tip about in here), where they concluded with bisque firing at a LOWER temperature rather than a HIGHER was better to prevent pinholes. to have higher absorption of the clay and pack the glaze particles tighter against the surface and have less ‘open space’ between the glaze particles (air that eventually will become pinholes..). this makes sense i think, but is also very confusing as it seems that the most common advice is to increase the bisque temperature to prevent the pinholes.. the only thing i was certain about was that i would try bisque firing higher, but now i’m not sure anymore. and if any of you bisque fire lower (08 or lower) as a rule, do you hold as well, or is a ‘slow program’ sufficient? if i bisque to cone 08 (as suggested in the podcast) and then test glaze fire a plate with no difference in the result; how much do i re-bisque the rest of the bisqued ware on (cone) to get them to as if they were bisqued at cone 04 to begin with? (if that made sense..) also, the pinholes appeared mostly in the speckled clay and not the blue. i was really sad about all these pinholes and desperately tried refiring them, again at cone 6; this time with all peepholes out. this resulted in even more pinholes and the speckles in the clay way more ‘melted’ than i like them. sorry for the loong post..any input? in advance, thank you.

@Callie Beller Diesel agreed, the contrast black clay/white glaze is really nice. thank you! that’s smart. i will try slooowing the bisque first then; hopefully that will make a difference.

@Hulkthank you so much for the thorough explaining of the cones and heat work and the chart. (puh, that stuff is best read when you are well rested i think, hehe.) i have understood that holding can give a result as if it is fired higher, but how much is a different story. this is really helpful. i have been meaning to buy some pyrometric cones, and now my supplier was out, but will definitely do! thanks again!

hello! i don’t know if this is posted under the right topic.. i am attending a christmas marked to sell my makings, and just recently discovered that it is outside. this isn’t until december, and the temperature may well be below zero (degrees celsius) at that time. now to my question: is it problematic for my ceramic pieces to be kept outside? i have understood that big differences in temperature isn’t optimal, and they will be going from (warm) inside temperature to possible minus degrees outside and then back inside.. if there is a little risky i don’t think i will take the chance, so are hoping for a 100% certain answer, hehe. it has mostly been bisqued to cone 05, and glaze fired to cone 6/7. in advance, thank you all!

@Hulk thank you! my kiln is not vented (but in a big vented space). previously i have only fired with all peepholes open with good results. this was actually my first ever fire where i closed both (side) peepholes after a ‘cold spot’ on a bowl my previous glaze firing.. but holding longer at the top temperature (with the peepholes open) during the glaze fire would maybe prevent this? or else how do one prevent this with all peepholes open? my pieces are relatively thin i think, hand built and about 0,4/0,5/0,7 cm (it differs a bit) looks like i need to save them up and fire only my black pieces (alone) together. ..and figure out how to make a ‘black-clay-program’ on my kiln.

@Callie Beller Diesel thank you! i actually had the same problem with a red clay a while back, but asked my supplier and he told me it probably wasn’t a good match to the glaze. (the same glaze as this time). i didn’t give it any more time or try to figure it out; but then this might be the exact same problem? the slow part (in both fires) seems to be key. but hold ‘starting’ at a higher temperature in the glaze fire?! thanks again.

@Min thanks a lot! also for the chart. i actually tried the e-mailing to myself (after advice from hubby) before giving up, but still same default message. hmm. i have been searching a lot in here and what i found is just what you say; holding at certain temperatures. and sloooow bisque in general it seems. i will definitely try that! (just need to figure out how to set a program on my kiln manually). i was aware of the need of oxygen, so at least nothing has been crammed in the bisque. thanks again!

@Bill Kielb i’ll definitely try lowering the temperature. and after searching the forum a lot the slow part seems to be the number one tip to success with the black clay. thanks!

@Rockhopperthanks a lot! didn’t think to search ‘black clay’. that’s super helpful. but then a higher bisque temperature and possibly an even slower fire may help. and i’ll research. or else hoping the dark-clay folks will chip in.

@Bill Kielb thanks a lot! i actually tried to post a picture, but got a message the file was too large and wasn’t able to shrink it.. i have to say i do always test my glaze. but usually i take a chance and try right away as well. this was my first time with the black clay, and i am a restless soul so the test-tile was in the same fire as the ‘test-plate’..hehe. the bisque was fired to a cone 05 with a two hour preheat and a slow program. not sure exactly how long the fire is though. the clay has a range between 1000 and 1240 degrees celsius and the glaze 1020-1200 degrees celsius. i slow glaze fired with a max temperature of 1203 degrees celsius i think, with a 15 minute hold. the guy in the ceramic shop told me to try a little lower glaze fire temperature next time because of the max temperature of the glaze, so i’ll try that. i also thought i would try a bit higher bisque temperature as well to let out more gasses. thanks!

hello potters! wondering if anyone can help. i have recently tried a glossy white (store bought but from powder) dipping glaze on black clay. the result was the whole glaze surface in tiny small ‘bubbles’. i asked my supplier and he thought there might be something in the black clay interfering with the white glaze. i can’t find any information on ingredients on the clay suppliers site about the clay. the glaze turnes out perfect on white and specked clay with the exact same firing temperature as the black clay. does this sound recognizable to anyone? i don’t make my own glazes (yet) so, it has to be a white store bought glaze. or maybe someone can explain what is the problem? can different clays with the same firing temperature need different temperature to mature the same glaze? hope this made sense, in advance thanks a lot! best regards, rebecca.