2Relaxed Posted August 12, 2020 Report Share Posted August 12, 2020 Not sure if this forum is correct for my question. Moderator, please move it if appropriate. I've made a lidded container for calcining some of my materials. It's greenware now, not fired. The question: do I need to bisque the container before using for it for calcining or can I simultaneously do both? Meaning, put my material in that greenware container and bisque fire all together. Why I'm asking? It don't fire often as it takes me a long time to fill the kiln. If I could calcine in the greenware container, I could then test glazes that contain the calcined material in the glaze fire that follows the bisque fire instead of going through another round of bisque. Link to comment Share on other sites More sharing options...
Min Posted August 12, 2020 Report Share Posted August 12, 2020 If it's a dark claybody then I wouldn't use it to calcine in, not that it would matter to the material being calcined but the pot might not have complete burnout of volatile materials therefore might have issues during the glaze firing. For a light body it should be okay. Link to comment Share on other sites More sharing options...
2Relaxed Posted August 12, 2020 Author Report Share Posted August 12, 2020 40 minutes ago, Min said: If it's a dark claybody then I wouldn't use it to calcine in, not that it would matter to the material being calcined but the pot might not have complete burnout of volatile materials therefore might have issues during the glaze firing. For a light body it should be okay. Oh. I haven't thought about the color of clay body. The container is made from my reclaim that is a mix of a bunch of cone 6 bodies (light and dark), as well as some raku bodies. The raw color of this clay is somewhere between terracotta and gray. When bisqued it turns pink. I was more worried about the material being calcined fusing to the body of the pot. I want to calcine Ravenscrag slip. Link to comment Share on other sites More sharing options...
Min Posted August 12, 2020 Report Share Posted August 12, 2020 2 hours ago, 2Relaxed said: I want to calcine Ravenscrag slip. You are actually better off roasting it, not calcining it. Ravenscrag will start to sinter at bisque temperatures, it gets gritty and won't go through a glaze sieve. Put it in a shallow bisqued bowl and take it up to 1000F and hold it there for up to an hour. How long you hold for depends on how much Ravenscrag you have in the bowl, if it's just a couple inches then 30 mins is probably good. Weigh it before you roast it then again afterwards so you know what the LOI (loss on ignition) is so you can factor this into your recipe. Link to comment Share on other sites More sharing options...
2Relaxed Posted August 12, 2020 Author Report Share Posted August 12, 2020 12 hours ago, Min said: You are actually better off roasting it, not calcining it. Ravenscrag will start to sinter at bisque temperatures, it gets gritty and won't go through a glaze sieve. Put it in a shallow bisqued bowl and take it up to 1000F and hold it there for up to an hour. How long you hold for depends on how much Ravenscrag you have in the bowl, if it's just a couple inches then 30 mins is probably good. Weigh it before you roast it then again afterwards so you know what the LOI (loss on ignition) is so you can factor this into your recipe. Min, thank you. You're right. I don't know why the term "calcine" got stuck in my head, the recipe calls for 1000F roast and that's what I'll do! Link to comment Share on other sites More sharing options...
liambesaw Posted August 12, 2020 Report Share Posted August 12, 2020 Calcine is an appropriate word for roasting to 1000f. You can calcine kaolin the same way, it doesn't have to be bisqued to drive off chemical water, that happens around 1000f. Link to comment Share on other sites More sharing options...
2Relaxed Posted August 12, 2020 Author Report Share Posted August 12, 2020 35 minutes ago, liambesaw said: Calcine is an appropriate word for roasting to 1000f. You can calcine kaolin the same way, it doesn't have to be bisqued to drive off chemical water, that happens around 1000f. Cool, thanks Liam! Still finding my way round all the terminology. Link to comment Share on other sites More sharing options...
Min Posted August 12, 2020 Report Share Posted August 12, 2020 Hey Liam, From Digitalfire, about 3/4 the way down this: "It is not actually calcining, since not all crystal water is expelled, so we call it "roasting"." I believe the LOI is up around 3% after the 1000F firing. I think this is one of those tomato / tomatoe scenarios. Link to comment Share on other sites More sharing options...
Min Posted August 13, 2020 Report Share Posted August 13, 2020 In a perfect world I'ld use a bisqued shallow pot. If you didn't crank the kiln up too fast my hunch is using a greenware dark clay probably won't make an appreciable difference to what is being roasted or calcined. Link to comment Share on other sites More sharing options...
liambesaw Posted August 13, 2020 Report Share Posted August 13, 2020 Yeah I use a red clay bisqued pot to calcine and haven't noticed any discoloration or ill effects, but I only calcine to cone 022-018 now so I'm not wasting energy during lustre firings. Link to comment Share on other sites More sharing options...
2Relaxed Posted August 13, 2020 Author Report Share Posted August 13, 2020 1 hour ago, liambesaw said: Yeah I use a red clay bisqued pot to calcine and haven't noticed any discoloration or ill effects, but I only calcine to cone 022-018 now so I'm not wasting energy during lustre firings. Huh, that's a good idea - to stick your materials for roasting in the kiln together with luster stuff! Link to comment Share on other sites More sharing options...
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