Plattypus Posted April 5, 2011 Report Share Posted April 5, 2011 Hello All, I have been told that Raku ware is really not to be used for food and drink. My clay is bisque fired to 04 and then we fire it in a gas out door kiln, transfer to buckets of straw, then douse in H20. My question is; is it really a bad idea to use the mugs for coffee? What do you think might happen if I was to re-fire the raku piece in our electric kiln with an 05 clear glaze? Would it change the raku finish? Would it make it usable for drinking? Please advise. Link to comment Share on other sites More sharing options...
Denice Posted April 6, 2011 Report Share Posted April 6, 2011 Hello All, I have been told that Raku ware is really not to be used for food and drink. My clay is bisque fired to 04 and then we fire it in a gas out door kiln, transfer to buckets of straw, then douse in H20. My question is; is it really a bad idea to use the mugs for coffee? What do you think might happen if I was to re-fire the raku piece in our electric kiln with an 05 clear glaze? Would it change the raku finish? Would it make it usable for drinking? Please advise. Food safe glazes go through many tests to make sure they don't leach unsafe chemicals in your food they are also checked for crazing which is a major factor in the Raku process. Then putting another glaze on top of it would start the testing process all over again plus you would probably have a reaction between the two glazes. On top of that the oxidation atmosphere would change the raku finish, I have refired some pit fired Anazai pieces that were fired so soft you could break them by looking at them. Most of the wood smoke pattern on them disappeared, I'm not sure what would happen to Raku. Historically people would get food poisoning on a regular basis from using improperly low fired dishes. Denice (Wichita, KS) Link to comment Share on other sites More sharing options...
Chris Campbell Posted April 6, 2011 Report Share Posted April 6, 2011 All of your raku effects would be gone in an oxidation firing since they are a product of a reduction process. Here is why raku is not safe for food ... Your clay has most likely not been fired to maturity so it would be very open, porous and the liquid would eventually seep through so the vessel would leak. This also means any liquid you put into it would soak into the clay and would be impossible to clean out. This means it would start to go bad, rot in those little holes and bacteria would start to grow. Ugh! Every pot does not have to fill every need ... Use your raku pieces to serve dry foods such as nuts, crackers, chips ... leave the liquids to properly glazed and fired ware. Link to comment Share on other sites More sharing options...
Idaho Potter Posted April 8, 2011 Report Share Posted April 8, 2011 I know not to use raku for foods with liquid, but no one has ever given me a satisfactory answer as to the use of tea bowls--fired by the family, Raku--in a tea ceremony. Been told the bowls are only used once; the boiling water kills any bacteria; the bowl is only used for tea so it doesn't matter. Pictures of bowls--both ancient and modern--show a crackle effect which would make a homeplace for bacteria to grow. I have made tea bowls, rakued them, served tea in them and tossed them. I aked this question at a Rick Hirsch workshop, and he didn't have a definitive answer, either. Comments and/or anecdotes are welcome. Link to comment Share on other sites More sharing options...
Chris Campbell Posted April 8, 2011 Report Share Posted April 8, 2011 Raku does not mean the same thing in Japan that it means here. We Westerners took the process and changed it to a decorative process leaving out the spiritual symbolism. I am not a fan of wikipedia but they have a good explanation of both processes ... http://en.wikipedia.org/wiki/Raku_ware Now, not to confuse the topic too much ... but a scientific study showed that the tiny cracks in crazed ware are not big enough to house even the smallest bacteria, let alone provide room for growth. Even more confusing! I don't like the idea of not being able to get serving bowls clean or to get color out of the cracks. That said, the teacup I am drinking from this minute is crazed and those lines are tea colored and I am not concerned. hmmmmmmmm Link to comment Share on other sites More sharing options...
Plattypus Posted April 9, 2011 Author Report Share Posted April 9, 2011 Raku does not mean the same thing in Japan that it means here. We Westerners took the process and changed it to a decorative process leaving out the spiritual symbolism. I am not a fan of wikipedia but they have a good explanation of both processes ... http://en.wikipedia.org/wiki/Raku_ware Now, not to confuse the topic too much ... but a scientific study showed that the tiny cracks in crazed ware are not big enough to house even the smallest bacteria, let alone provide room for growth. Even more confusing! I don't like the idea of not being able to get serving bowls clean or to get color out of the cracks. That said, the teacup I am drinking from this minute is crazed and those lines are tea colored and I am not concerned. hmmmmmmmm I agree hhmmm. I read the wiki.. (mostly). I didn't see mention of a scientific study. Did I miss it? If you don't use milk in your tea do you really have anything to worry about? the tannin from the tea shouldn't be a problem (to my mind)... If there was another source for that study would you kindly post it? Link to comment Share on other sites More sharing options...
Guest HerbNorris Posted April 9, 2011 Report Share Posted April 9, 2011 I am all for exploding "ceramic myths" or "clay myths" when they stand in the way of real progress and understanding. It helps everyone to get the truth out there. Coffee and tea are acidic, which would accelerate the leaching of any metals that are in your raku glazes. What is in your raku glazes? Do you know for sure? Copper? Barium? Manganese? If you are like me, you have more than one cup of coffee or tea a day; I have several, and I use my mugs for other liquids, which I don't really "monitor" for acidity all that much. I might have a cup of tomato juice or orange juice, both acidic. Over time, with multiple uses, a lot of leaching of glaze ingredients could occur. I will pass on that, thanks! Because my mug is not a raku mug, I don't have to worry about that. Also, coffee and tea are usually served hot or warm, and this would increase the speed of any leaching. I also have left coffee sitting in a mug for most of the day, and then rewarmed it in the microwave, which would really allow migration of the metals into the liquid. Nowhere, in any book, magazine, internet article, or at a show have I ever seen anyone advocate using Raku ware for food use of any kind. It's too bad, because I (and thousands of other people) would LOVE to be able to have functional Raku ware. If you really want to drink coffee out of a raku mug, then why don't YOU do it? Then you can report back to us here and we all can see what the results are. You just might be the one to explode one long standing "ceramic myth!" Link to comment Share on other sites More sharing options...
Idaho Potter Posted April 9, 2011 Report Share Posted April 9, 2011 Hmmmmmm, indeed. I, too, use a crackle raku tea bowl for tea--only tea, and only for me. Anyone who has purchased raku pieces from me is told not to use them for food. I guess I'm willing to take a chance, but unwilling to be responsible for someone else getting sick. What they do when at home, I'm not privy to, so have no say in the matter. I have used small raku flat plates for hors d'oeuvre after covering them with the ever elegant Saran wrap--not the best solution. I read the wiki info (all) and found no mention of a scientific study, so, Chris, if you could point me and Plattypus in the right direction . . .? Also, never having used Wikipedia before, I don't know how to get them to correct the reference to Rick Hirsh (noted in red which means no info). Correct spelling is Richard Hirsch. Link to comment Share on other sites More sharing options...
bciskepottery Posted April 10, 2011 Report Share Posted April 10, 2011 John Hesselberth and Ron Roy, in Mastering Cone 6 Glazes, describe a number of tests you can do to assess the durability and fit of glazes (equally applicable to low, medium, and high-fire temperatures). For acidity, they describe a lemon wedge and a vinegar test, for example. The tests are described in detail in Chapter 3. If you have real questions, you can always send a cup to a professional laboratory (listed in the book) and ask for a testing for leaching. Hesselberth and Roy use drinking water leaching standards for their tests; unfortunately, there is no standard for ceramics. Due to variations in raku firing techniques and temperatures, you may not get the same (or repeatable) results from each firing. Durability and fit are both the result of both the glaze contents (recipe) and your firing schedule. Link to comment Share on other sites More sharing options...
Chris Campbell Posted April 10, 2011 Report Share Posted April 10, 2011 Why anyone would want to use a raku piece as a daily mug is a mystery to me ... you would just be accelerating the deterioration of the wonderful reduction effects even if you did not care about improperly fired wares, leaching chemicals, leaking pots and ruined tables. Raku ware is not fired to functional standards. As a simple test, try washing it in warm water and notice how long it takes for the mug to dry ... it takes a long time because the water has soaked into the clay not run off it. Like people, one piece of pottery does not have to fulfill every single need you have. The study was mentioned years ago on clayart when everyone was arguing for perhaps the hundredth time about whether or not crackling was dangerous due to growth of bacteria. The study was quoted re: bacteria was larger than most crazing and would not survive there, never mind reproduce. Not enough room to do so. Cannot do better than that and have no wish to search their massive archives for it. Link to comment Share on other sites More sharing options...
fontaine Posted June 1, 2017 Report Share Posted June 1, 2017 raku and water . I don't know what to think. Every year I go to japan to meet my japanese potter friend and to refine my skill. In japan people drink tea in raku cup and not problem. When I asked the question to my friend about "raku not holding water?" he could not understand why I am asking the question since for him it was irrelevant. https://ulujm2.wixsite.com/jmf3d Link to comment Share on other sites More sharing options...
Guest JBaymore Posted June 1, 2017 Report Share Posted June 1, 2017 raku and water . I don't know what to think. Every year I go to japan to meet my japanese potter friend and to refine my skill. In japan people drink tea in raku cup and not problem. When I asked the question to my friend about "raku not holding water?" he could not understand why I am asking the question since for him it was irrelevant. https://ulujm2.wixsite.com/jmf3d Japanese Raku is quite different form American Raku. And for Chawan........ even American Raku... if done appropriately... could be used. Need to address the post firing reduction potential of toxins and the loose carbonization materials that will be in the pores of the clay. And formal Tew use places different demands from "American food use". In Japan I too use Raku works for Tea. And I have Japanese Raku Chawan that I use for Tea here also. best, ....................john Link to comment Share on other sites More sharing options...
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