Ceramic Glaze Tests - Raw Fired vs "Double Fired" vs Regular
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- Опубліковано 17 лип 2024
- I show a series of test bottles subjected to three different firings on two different glazes. Firings were done at Cone 05 and Cone 5 in an electric (oxidation) kiln.
I want to know two things:
1. How does raw firing effect glaze color?
2. Can I under-fire a glaze, damaging it with crazing, and then re-fire to "heal" the glaze?
Please leave me a comment if you have thoughts, want to share your experience, or are inspired to try something new.
Enjoy.
Amazing spirit of experimentation! Love it! We all benefit from you sharing your discoveries. Thank you!
Love your experiments, makes me want to try so much stuff that’s not the usual 👍
Thanks for the demo. I prefer the raw-fire look but also liked the oil-spotting effect you got.
Super cool experiment! I love your videos - keep on going!!
Thanks!
Love the seafoam double fired thinner dip. The second bottle. Love the color change.
Hey these are some of the best art videos I've ever seen- the jazz interlude gives this 100% on rotten tomatoes. I wanted to suggest maybe leaving your notes (text) up on screen like 20% longer - I found they're there/gone almost too fast for me to process and the info in them is gold so having a few extra seconds to process would be great. Love your work!
I feel like a follow up stress-test between the raw fired vs. traditional would be cool to see if there's value in the bisque.
Why the heck do we bisque fire, if you can get good results with just one glaze fire? So cool! Thanks.
Raw Glaze is like Hardening Steel, just the outside is hard. While Bisque creates holes from the organics being burnt out. When you glaze after a Bisque, the additional material that "hardens" goes into more pure surfaces, giving the product a harder resistance to breaking and shattering. So it's like a temper to the "edge" of a blade versus hardening, which still makes the piece brittle.
Love that tile!!
Thanks!
Awesome info. Question: though not optimal, is it possible to successfully re-glaze and re-fire an item that didn't glaze well? What cone would I use and would that be on a medium firing? Also I've heard I can use hair spray to keep the re-glaze from sliding off the vitrified piece. Is that a myth? Thank you for your continued guidance!
That’s a really good experiment!!! Why firing schedule did you use? I usually just use the program setting in my kiln…. Is it a special type of firing schedule?? Thank you for sharing
As I commented in another reply, I'll share here.
The Concept of a Bisque is to create more pores and openings for glazed to seep through and absorb into. Sometimes you can get color changes, but the purpose isn't related to color. It's strength. Glaze is used as a hardening surface, that's what it was meant for thousands of years ago, for sealing surfaces and hardening for protection.
So when you think about the pores being opened in a bisque and then the concept of the glaze going inside, when the glaze is fired, it's fuzing micro pores throughout the entire piece. It's like Velcro, the tiny pores that dig into the bisque surface are connected to the outside glaze, thus making it stronger.
While raw glazes are quick and simple, the impact resistance and limit structurally to the piece is decreased nearly 30-35%. There are a few NSF research studies on the structural engineering side of the same concepts, I read them several years ago and can't find the links right now.
Also, the reason you didn't have blistering in the raw fire in these concepts, is from the inner portions and outer portions having places to escape. If you covered the full piece in glaze, there would be no areas for the air to run. So that would cause blistering.
I was working with this glaze once called Wilford blue and it crazed like you wouldn't believe, but only when it was layered on top of another color. Particularly Satin Black. The Wilford Blue I was working with was also really fickle in its consistency, too thin a layer and it would just pool in the bottom of the vessel when fired, too thick and it would flake off as it dried before the firing. No two results would be exactly the same.
Is it possible that the crazing on the tile is likely more visible because it was fired flat (presumably), giving the glaze more room to retract compared to the vases which would be fired vertically?
One other thing to try... I fired my floating blue again, but to cone 04 and got a WILDLY different glaze color.
Interesting...... I think I will have to try that.
I have seen a lot of your videos and I don't think I had seen you throw before. What kind of wheel are you using? Is it a diy project too?
Would the fact the tile was flat make a difference? The glaze wouldn’t run down. I do like the once fired. Did you raise temperature slowly to remove moisture?
Not sure about the flat tile. Maybe my application of glaze was different because it was flat. I didn't fire them with a different or slower firing. Probably isn't a bad idea, but I fired in my normal way for a Cone 5.
I am just venturing into ceramics, and I'm a little lost. I understand the first pair was fully dried greenware that was dipped once, allowed to fully dry again then bisque fired - at which point they looked dull and virtually identical. After a second fire they looked glossy, distinct and "finished" looking. Got it. I also understand he then did the same thing, but triple dipping. Also got it. But the "raw"" versus "regular" I don't follow. I assume regular means fully dried greenware is bisque fired, then glazed, then dried and fired. What is the "raw"? If raw jus means glazing greenware why doesn't it look like the first example of the first pair? Why doesn't it look dull and drab? I thought the first pair showed that's what happens when you glaze greenware and fire? So confused! Any nfo greatly appreciated - I'm still learning!
By "Raw" I mean that there was no bisque firing. Just glaze firing (Cone 5), which will make the glaze glossy due to temp. I really wanted to know if glazing a "raw" bone dry unfired pot to glaze temp would look the same as a "regular" pot that was bisqued then glazed and fired. How nice to know that if you were filing up a kiln for a glaze firing and had a bone dry greenware laying around you could give it a dunk and throw it right into a glaze firing and it would look the same. I hope that helps.
@@JustinsMakeryAAh! Got it! Many thanks!
The crazing might happen because of shrinkage, perhaps test the glaze with shrinkages of the clay body in mind. I can think of varying the wetness of the clay body, using a blow torch, the difference might be because a tile as a flat surface will contract differently when drying. Just some ideas.
At a look up in a book, crazing is caused by expansion of the glaze. Glaze behaves ‘better’ under compression than expansion. Apparently rapidly cooling the kiln can cause crazing, (just think of raku) perhaps rapidly cooling your biscuit firing, which has glaze on it, will cause the crazing. Then you can reglaze in clear.
That's an interesting idea. Thanks!
Okay, I am waiting for my first wheel to arrive. I have a question, please don't judge me as I am here to learn :) And no I will not be "firing" my pottery in my regular oven, that's not pottery- just dried clay. I will be basically renting a kiln (bring your pottery, they fire it for a fee). So, my goal is to fire it only once to save some buck. My question- would it make any sense to try and dry out the pottery as much as possible in my home oven, then glazing it, then firing it in a kiln?
I am asking this simply because apparently the cracks happen when moisture is leaving the clay. I am wondering if this would help with glazing, simply because 250 degrees Celsius seems better than room temperature air drying?
They say it helps, but I didn't try that yet
I raw fired an entire chess set. I had applied a cone 05 underglaze but no overglaze onto bone dry pieces and fired them once and they turned out marvelous. I was using local dug clay which is most likely earthenware. I don't know that the clay is fully matured bc my kiln only goes to 2000 degrees F. The pieces are still porous, but this is a chess set.
What is the clay body..porcelain?
Cone 5 B-Mix