What Glaze Recipes Can Tell You
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- เผยแพร่เมื่อ 15 ก.ค. 2024
- Welcome to The Potter’s Round Table, the topic today is What Glaze Recipes Can Tell You.
Want to get some idea of what a glaze might be like before you make it up? Glaze names and titles do not always accurately and completely describe the glazes. Once you have learned a little about common glaze ingredients, you can look at glaze recipes and often find clues about how the glazes will perform. This discussion reviews the three categories of glaze ingredients (fluxes, stabilizers, and glass-formers) and their various influences on glaze properties, and how we can predict some glaze properties by examining over twenty glaze recipes.
The Potters’ Round Table is a production of Washington Street Studios. As a result of the pandemic the Round Table is hosted as a TH-cam livestream event and then edited to be added to our video library.
Show notes, including handouts, can be found at www.hfclay.com/the-potters-ro...
The Potters’ Round Table is brought to you by Washington Street Studios, a community pottery studio, gallery, and pottery school located in Harpers Ferry / Bolivar, WV. We exist to provide ceramic artists an affordable, fully equipped studio space for aspiring, emerging and established artists to share their creative energy and knowledge in an environment designed to support the ceramic artist. If you want to learn more about Washington Street Studios, visit our website at www.hfclay.com/.
At Washington Street Studios, we believe the sharing of creative energy and knowledge will improve the quality of our art and increase the appreciation of art within our community. We are striving to create an environment where the arts are shared and appreciated. We want to grow as a family of artists and contribute to our community.
This video is one of our steps to share our passion for the ceramic arts, creative energy and knowledge with other artists and art lovers. We also created an audio version to expand our audience. If you are looking for the podcast of our show search for the ‘The Potters Round Table’ on your podcast platform of choice or go to anchor.fm/thepottersroundtable.
Very informative, thank you so so so much.
Glad it was helpful!
Excellent teacher,worthy of a national foundation or fellowship
Dennis caffrey, thank you for your kind words. We hope you enjoy all the videos!
I just found this channel after returning to pottery after an 8 year break. I am taking it all in. Thanks for creating this content! Phil was a genius! Very engaging. I'm sorry to hear that he passed away! My condolences!
Thank you Kimberly and best of luck in your pottery adventure. This channel will continue in some form or fashion!
We received the following question via email: Throughout the video you discuss fluxes which melt at different temperatures. How does this affect the impact of substituting ingredients in a glaze? For example, what if I wanted to remove Gerstley borate from a recipe and replace it with Ferro Frit 3134. By adjusting the percentage of the other ingredients in the glaze, I could match the original chemical components, i.e. sodium, potassium, calcium, etc. But now I would be sourcing the boron from a frit rather than the Gerstley borate. I assume that this would affect the melting temperature and final result.
And Phil's response: Thanks for your question. There shouldn't be much difference if Gerstley borate is replaced by Ferro 3134; they both melt at bisque temperatures. The frit might melt a little more uniformly and faster than the Gerstley (because of the impurities), but at a moderately slow firing speed, I don't think that you would see much difference. This wouldn't be true for other substitutions where there was a big difference in the melting/fluxing temperatures, such as between whiting and a calcium frit. As long as the substitutions provide the proper chemical compositions, there shouldn't be a difference in the final results of proper firings, but the differences in melting temperatures can show up in the way that the glazes can interact with other glazes (overlaps) or in the optimum firing schedules required.
Phil
I love and learning very much with your videos here in Brazil. Thank you millions.😊😊😊😊😊
Thank you for the encouragement and please share the channel with your friends and fellow potters to help us grow our community!
Thankyou..learning so much..
Julie, did you go through the Understanding Pottery series? If not you should check out the playlist (th-cam.com/play/PLS6Mrdpt53RyauAg8bGN-7HtqIokbwUKF.html) to go through the entire series in order. Thank you for watching and share the channel with your friends and fellow potters to help us grow our community.
I just found your page and love it. Could you please do a presentation about low fire glazes ... I am interested in making 04 and 06 glazes to use when I bisque fire! :). I use a gas kiln and am looking at cost effective glazes for mugs.
Thanks so much.
Michele, we are very happy you found us! Phil is going to work up a talk on making low fire glazes. We have a few topics already scheduled but you should see the video in a couple months.
Thank you again for the great video!! I noticed that in some of the presented recipes, bentonite is stated as additive although it's a clay and can work as stabilizer if I'm not mistaken. Just wonder why it is in the additive then? Also, I wonder how to test matte glazes for food safety?
I'll send this to Phil and post his response! Thanks for the questions.
Hi Anna,
Thanks for your email and question. Bentonite is generally treated as an additive because of its somewhat unusual properties: extremely fine particle size and the ability to absorb a lot of water. These properties make it useful for helping to suspend wet glazes, but if used in large amounts it causes high drying shrinkage in glazes, resulting in cracking and possible crawling. So, it can only be used as an additive in small amounts, typically 2 percent or less, and not as a major ingredient in glazes. But you're right, it is a clay, and when a glaze melts, it can contribute to the stabilization.
The only sure way to test glazes for food safety is to submit them for chemical analysis using the leaching test. However, you can always try the lemon test for a first indication (put a slice of fresh lemon on the glaze, let it sit overnight, and see if the glaze is changed). Looking at the glaze recipe can tell you if there are any potentially harmful ingredients (such as copper compounds greater than a few percent) that might be of concern. Matte glazes can be less food safe than glossy glazes in general because they often contain very small cracks that can't be seen with the naked eye (microcracks), and some matte glazes are matte because of actually being underfired, which makes them less stable.
Phil
@@WashingtonStreetStudios Thank you so much for such a detailed explanation, Phil!! It's much more clearer now! I can't stop saying thank you to the WSS team and appreciating the work you're doing. It's just so great to have such a responsive and informative resource! Happy holidays and all the best to the whole WSS team! Hope you all are staying safe!:)
Thank you Anna, please share the channel with your friends and fellow potters to help us grow our community. We hope you had a wonderful Christmas and may the new year bring you happiness and joy!
Hi, thanks for the video! Where does the Blue color come from in Recipe 4, please?
I will send the question to Phil and post the response when I get it back.
Hi Vincent,
Thanks for your question. Number 4 was the recipe for a general base glaze (no additives) that was used at The Odyssey Center, in Ashville, N.C. Unfortunately, I don't know specifically what additives have been used, but no doubt a cobalt compound (cobalt carbonate or cobalt oxide) was included as the main source of any blue coloration. Sorry if that was a little misleading.
Phil
Thank you, great video. Does it means Zinc or Boron is necessary to get a 6 cone glaze?
A glaze with zinc or boron will not be a high fire glaze, and there are mid fire glazes that don’t use zinc or boron.
@@WashingtonStreetStudios Thank You.
Thank you - I have a further question. You answered "... there are mid fire glazes that don’t use zinc or boron". My final question is: Does it means Lithium, Zinc or Boron is necessary to get a 6 cone glaze? Thank you very much :)
I am sorry, I can’t answer your question, and Phil passed away last year, so I have lost my best resource! I don’t think all cone 6 glazes have zinc, boron or lithium. Cone 10 glazes will not have these ingredients. Did you watch the glaze chemistry videos?
@@WashingtonStreetStudios Oh, I am so sorry! What a loss... I found the answer: Cone 10 does not need additional fluxes to melt. But: Cone 6 needs additions of fluxes - Zinc (Bristol Effekt), Lithium (not so good) or Boron (best - brought in with Frits or Gerstley Borat). You need to have a cone 6 glaze an addition of 0,15 Mol B2O3, otherwise it will not melt properly. All the best for you.
May I ask, what would be the most effective way to increase the crackle to the glaze? I read online and it says to increase the silica and clay ratio to 1:1.25. What method would you recommend?
Thank you for the question! Unfortunately Phil was the glaze chemistry expert and he passed away in July of 2021. I would check John Britt, best glaze guy I know today.
Thank you for this great video. When talking about Whiting, he says it's calcium carbonate, which I'd learned, but then he says it's calcium oxide. What's the difference?
Cady Cash, good question. Calcium carbonate (CaCO3) when it is heated burns off carbon dioxide (CO2) and leaves Calcium Oxide (CaO). In a glaze, when you use whiting, Calcium Oxide is the compound that remains in the glaze, or combines with other minerals and compounds, to create the final glaze effect.
Thanks for watching and please share the channel with your friends and fellow potters to help us grow our community.
I noticed that in a lot of the examples the glazes that form a significant amount of crystals instead of a purer glass (resulting in a Matte/Satin/Dry look) Phil states that It may not be food-safe depending on the colorants used that may leach out. My question is if by limiting the resulting looks (to only clear/shiny/transparent), the firing temperature, and the amounts of oxides and carbonates used as colorants I can build a safer practice in terms of food-safe pieces without the use of professional chemical analysis. Is there a regulations manual or written guide to help identify which oxides/carbonates I can use and under what conditions to ensure the safety of the pieces? I'm quite a bit lost on this particular matter and could use a good reference. Thank you.
Thanks for the question, I've forwarded it to Phil and will post his response. I've also suggested a future video on how to determine if a glaze is food safe?
@@WashingtonStreetStudios Thanks! ^^ A video on that topic would be amazing! Hoping to see it.
Hi Matheus,
Thanks for your question. As a broad generalization, shiny, transparent, uncrazed glazes are probably more likely to be safe with respect to leaching of colorants and other ingredients than matte glazes, but the chemical composition would still be important. Certain safe glaze compositions for one colorant might not be as safe for other colorants. It can be a complicated situation with different requirements for different colorants and other glaze ingredients. I am not aware of any manual or general "guide" for producing safe glazes because there are so many variables involved. Of course, the lower the concentration of the colorant, the more likely the glaze would be safe. Utimately, there is no sure substitute for chemical testing.
Phil