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Min
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Posts posted by Min
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This is a bit like which came first the chicken or the egg.
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Stacking determines the load. I cut out a posterboard template of kiln shelf that I put the pots on for each shelf. Planning starts at the design level when possible. For example if I know I'm going to have a bunch of wide bowls to fire I make sure I have pots that will fit in the shadows to maximize shelf usage as much as possible. I try and have a lot of bisque on hand so I can plan the load to have as little dead space as possible.
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43 minutes ago, BobMagnuson said:
Now, if there are reduction fire zinc crystal glazes, that's a different story. If zinc crystal glazes can survive reduction fire, then zinc loss due to volatilization probably isn't very important.
Crystalline glaze potter, Dianne Creber has some pots done with reduction but the reduction is done after the pots have been fired in oxidation to cone 10. She does either a refire to a lower temperature or starts reduction on the way down from an oxidation firing. From the upper end of 1900F down to 1250F reduction to change the colouring oxides. I remember doing button tests of all the glaze chemicals, there was nothing left of the zinc oxide when fired in reduction to cone 10.
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Had a thought about something when posting the recipe above in regards to the whiting. Looking at the eutectic chart, if we know the temperature for the boron calcium melt is 990C/1814F and we know the LOI for whiting is roughly 45% then using sideways logic it would make sense to go slow and possibly do a hold around 990C/1814F to clear the bubbles in boron glazes containing a significant amount of whiting. Does that seem logical?
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30 minutes ago, BobMagnuson said:
Does anyone out there have a successful reduction glaze recipe that includes zinc?
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@BobMagnuson, wondering about zinc eutectic and reduction. If the temperature for zinc oxides eutectic point is 1030C / 1886F (using 0.54 CaO + 0.46 ZnO + 0.13 Al2O3 + 1.39 SiO2) have you found a difference between oxidation and reduction eutectics for zinc given zinc will start to volatilize in reduction around 900C?
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On 5/13/2021 at 5:39 AM, Dick White said:
this glaze chem stuff IS wilderness camping
Or....it could be viewed as another map, to help get out of the chem wilderness.
Adding my voice to say thank you to @BobMagnuson for both sharing his calculator plus making himself available here for questions and comments.
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Hi Bill,
Okay, so I'm just poking around with the EuCalc, I'm using a Mac. I took Sue McLeod's clear from Glazy and plunked it into the calc. Don't know if one would get the same results using Excel? Looks like there is excess alumina and silica that isn't taken into the melt but I could be reading this wrong. I'm heading out early tomorrow a.m. to go wilderness camping, won't have a chance to play with this some more until I get back Sunday night.
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There was a recent thread where glaze eutectics was brought up. Stemming from that was a link to an article by Robert Magnuson in the Feb 2018 Ceramics Monthly which contained a link to a eutectic calculator, "EuCal", he created. Magnuson discusses an interesting aspect of eutectics, to quote from the article:
"One of the most interesting aspects of eutectics isn’t how they melt, but how they solidify. When a eutectic mixture cools from the molten state, the individual components all stay molten together until they solidify. When they do, a transparent glass is formed. If the molten glaze contains ingredients that are not part of a eutectic, these ingredients may solidify separately while the glass is still liquid, leaving tiny crystals suspended in the glass, producing opacity and other effects in the final glaze. But, if a glaze contains only eutectic mixtures, a transparent glaze will result.
Very few glazes are based around a single eutectic and most incorporate both alkali (R2O) and alkaline earth (RO) oxides. Any combination of the eutectics of Na2O, K2O, and CaO (see left) will result in a transparent glaze. For such a neat trick, it’s surprising you don’t hear about it more often. If you have ever tried to formulate a fully transparent glaze by trial and error, you know it isn’t easy to do—unless you know this trick."
Since the time of that publication Magnuson has updated and revised his EuCal. Version 1.8 added borate eutectics for the alkali fluxes and the latest version, 1.9, added a calcium borate eutectic. This could be very useful as it now brings mid and low range glazes into play with the calculator. There are some provisions, see the read me file linked below.
Given that not everyone has access to the links in the article Jennifer Harnetty asked Magnuson for permission to link the read me file plus the eutectics calculator here to which he very kindly agreed to. I've added the links to the updated version below.
I realize this isn't an area that gets a lot of discussion but perhaps as time goes by as more people get familiar with the calculator it can be utilized as a stand alone piece of software or perhaps in tandem with Stull charts. Lots of food for thought here.
Link to the Feb 2018 article here: https://ceramicartsnetwork.org/ceramics-monthly/ceramics-monthly-article/Techno-File-Using-Eutectics
Link to the User File here: https://ceramicartsnetwork.org/docs/default-source/default-document-library/eucal_1_91_user_guide.pdf?Status=Master&sfvrsn=a5d9b703_5/ EuCal_1_91_User_Guide.pdf
Link to the EuCal here:https://ceramicartsnetwork.org/docs/default-source/default-document-library/eucal_ver1_91.xlsm?Status=Master&sfvrsn=6fc99709_9/EuCal_ver1_91.xlsm
- blackthorn, Roberta12, Pyewackette and 4 others
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@Magnolia Mud Research, I just had a look at the 5 low-fire clays from Plainsman that I have access too. Don't know if you are familiar with the write-ups from Plainsman but they are very good. (Tony Hansen does the clay tech) Anyhow, was pleasantly surprised to find that 1 of the 5 might actually be fine. It fires to a dark brown at cone 2 with a posted absorption of 0.5 - 1.5% The other 4 don't appear suitable as the absorption is still too high at ^2 (ranges from 2-10%) and firing some of them hotter leads to a brittle or bloated claybody or doesn't bring the absorption down low enough. Something to experiment with for sure (when I can carve the time out for it), although I would prefer to stick with white claybodies.
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I'm all about durability and functionality with most of the pots I make, I like my clay vitrified to the point that it won't leak without glaze, for me it's midrange stoneware or porcelain. Would be great if there was a commercial body that was in the cone 2-3 range that met those requirements. I'ld gladly pay a bit more to fire lower than ^6 and yet have a clay that would be less expensive than a lowfire fritware body. Would probably need to use more frits in glazes than I currently use at ^6 but I think the decreased wear on the kiln elements (and kiln itself) would more than offset that cost.
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@Pres, when protection tubes are placed over the tc's it cools down how they read. I believe for L&L protection tubes they say it's 18F. Looking at those cones I would guess you got well over 18F hotter than cone 7.
Is putting a cone pack in front of a peep an option? I wouldn't risk an entire load without being able to see the cones during the end of the firing for a new kiln, shut it down when your target cone is down, record the temperature and go from there. I'ld do this for both a bisque load and a glaze load. Just checking, you didn't have a soak at the end of the firing?
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21 minutes ago, ClayKatie said:
Also i have read that for these high fire clays ^10 is the max firing temp it can take, but in many applications firing lower is fine.
If you are making functional ware from either a mid or high fire clay then the clay shouldn't leak even when there is no glaze on the pot. Absorption of under 1.5% is ideal.
Clay is at it's strongest when fired to maturity.
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What do your witness cones show? Are you getting to cone 9 with that schedule?
Laguna's published absorption for the ^10 B Mix with sand is 1.2% and the Maya Red is 1% but these both come with a fudge factor of +/- 1%. I'ld suggest doing your own absorption tests and seeing what your actual absorption is. Link to how to do that here if you need it, about 1/2 way down. Do the proper test with weighing and soaking a sample or two. Since staining of the unglazed clay could be an issue I'ld aim for 1% or lower absorption which I'm guessing you will be over.
I can understand your concern about firing to cone 10, maybe time for a road trip?
Welcome to the forum.
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A plethora of oxide wash recipes from June Perry here. She fires cone 10 but changing the feldspar to either gerstley borate or a boron frit like 3134 would be a place to start testing them at cone 6. I wouldn't recommend any of the ones using barium.
@Missy, I've use 30 Red Iron Oxide + 30 Blackbird (an iron plus manganese clay) + 30 Alberta Slip + 10 Rutile at cone 6 for a similar colour as in your image.
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Re new elements (in a new kiln or replacements), from one of the Kanthal Handbooks from the wire manufacturer Sandvik in Sweden there is this advice:
"Pre-oxidizing the elements is recommended for customers using their kilns at elevated temperatures (cone 6 and higher), or under corrosive or reducing conditions. To oxidize the elements, heat your empty kiln to a temperature above 1922F/1050C with the peep holes open and the lid raised slightly. Holding the temperature there for 6-8 hours will ensure thorough oxidation of the elements, but most of the oxide growth occurs in the first 1-2 hours. This procedure grows a protective oxide coating on the elements before the elements are exposed to any harmful atmospheric conditions. This procedure is usually only done once, but can be repeated as required if the kiln is fired under harsh conditions such as a reducing atmosphere (which actually removes the protective coating)."
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A quick look on Standard Ceramics website shows quite a few combinations using the 1198 Layering Base. Link here. Looks like it adds visual texture to all the glazes that were put over it.
Congrats on your new kiln!
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My suggestion for a QOTW came about from this thread. The thread drifted a little to include a members comment that cone 6 electric is easier than cone 10 gas reduction. My initial thought was yes firing an electric kiln is less time consuming than firing reduction but there are tradeoffs.
I’ve always found cone 10 clay nicer to throw than any of the midrange clays I’ve used, the glazes (and clay) are generally less expensive to make for high fire and I also agree with what Michael Cardew said, electricity is a harsher judge of pots than reduction. I find that gifts from the kiln are far less frequent with electric firing vs reduction. Wood firing would top my list as the most work.
So, electric or gas reduction firing at any cone you choose, which is more work overall and at what stage of the pot making is it more work than the other? Also, is firing one way more enjoyable than the other?
And to make this into a 2’fer QOTW suggestion, another question would be this: hypothetically speaking if zoning / bylaws / fuel cost didn’t come into play would you glaze fire gas reduction or electric?
- Rae Reich, Pyewackette and Pres
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One females take on this...It's not so much that the scene in Ghost was staged, it's a movie and it's expected. What does bother me about it is when some random guy at a market gives me a pervy look and asks something along the lines if I make pots like that. ick!
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When I use wood batts (high density fiberboard) I wire off as soon as I've finished throwing them. Thickness of the wire makes a difference, doesn't have to be a wiggle wire just a thicker wire will do the trick if they are re-sticking to the batt. Also, just make one pass with the wire, if you run the wire under more than once you can get little wafers/layers that are more work to deal with when it comes to finishing the bottoms, especially if you use a sticky high ball clay body.
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2 hours ago, Denice said:
You can't throw out your clay slop on the ground?
Red clay + dog + cat = mess. Guaranteed they would find a way to track it indoors! I guess I could have dug a hole and buried it though.
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Speaking of cleaning, I tossed a mostly empty bucket of red clay slip in the garbage about a month ago. There was about 500mls left, sloppy but not super wet. Was out for the day then around dinner time there was a knock on the door. By-law enforcement officer with his pad out and a ticket written up for $250- He said "I think you know why I'm here." Nope. Pulls out his phone and shows a photo of the white garbage truck with 2 red egg sized splotches down the side of the truck. He said the garbage truck driver stopped doing his collection, called by-laws and sat there until they showed up then took a picture of my garbage can and the truck. Explained to him it was red clay. Didn't believe me and said the garbage man said it was red paint. I went with a flashlight out to the garbage can and showed him a bit of the clay that was on the rim of the garbage can. Must have pulled his ticket pad out around 10 times during all this. Got a stern lecture about throwing red clay in the garbage. I asked him what was I supposed to do with it to which he said put it in the green waste bin. Didn't care for it when I asked if that would have stopped it dripping on the truck.
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1 hour ago, Denice said:
Dust storms have silica in them, silica is everywhere.
Yup! About 60% of the earths crust is silica. Neat video showing "dust" from the Sahara travelling thousands of miles. Diatomaceous earth is approx 80-90% silica, much of the Saharan dust is diatomaceous earth from dried lake-beds in Chad. Not saying it's okay to have sloppy studio hygiene but keep it in perspective.
American Beauty Glazes
in Clay and Glaze Chemistry
Posted
@Clyf, try sending a pm to the member(s) who had some for sale. Just click on their avatar then the blue "Message" box that will be on that members homepage and follow the prompts. They will get an email letting them know they have a message on the forum.