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Min
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Posts posted by Min
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Hi and welcome to the forum.
Whereabouts are you looking for a large kiln? Country? Location?
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Hi and welcome to the forum.
Might not have been the unloading at 320 (F?) that lead to the crazing. If this glaze normally doesn't craze then it probably crazed because it was underfired.
2 hours ago, Lightbeaming said:my question is- will refiring at a slightly lower temp (^4/^5) fix the crazing and help the glaze reach maturity, or are the pieces too far gone at this point? Also, what are some precautions and potential mishaps if I go forward with said firing?
Again, does this glaze have crazing usually? Do you know what cone the kiln got to?
Refiring a mature piece to the same cone is usually a crapshoot, glazes can run and clay can bloat. How fluid is your glaze? If it tends to run then put some waster slabs under your pots to catch glaze drips / runs. Could you test a couple pieces fired to a hot ^5?
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@bees.and.stones, please let us know if any of the glazes linked work for you. Bill's glaze is a great example of how one glaze can work really well for one person and not so much for someone else and the importance of test tiles to try out a glaze before committing good work to a new untested glaze. Glaze recipes often don't travel well. Given that you are in Europe your materials could well have a different analysis from what's available in North America.
My test tiles of Marcia's Matte from Bill's link above. Ink stained and cutlery marked with a rough unmelted surface when I tested it a couple years ago. Black underglaze stripes on 3rd test tile.
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I would strain some of the bits out, rinse them off to see the shape of them then try and dissolve some in hot water, see what happens.
@Jeff Longtin, have you worked with slips containing a lithia spar, wollastonite or a boron frit? Any thoughts on what this is from?
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Which recipe are these from?
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Transparent matte is a bit of an oxymoron. I agree with @High Bridge Pottery, some of those pots look like they have an immature glaze, maybe an underfired gloss.
- High Bridge Pottery and Pres
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Glazy might be somewhere to start looking then testing.
I put midrange + transparent matte into the search parameters and these came up: https://glazy.org/search?keywords=transparent matte&base_type=460&cone=mid&analysisName=xUmfAnalysis&photo=true
Welcome to the forum.
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@Jeff Longtin, type of wax resist makes a big difference in how well this works. Use a water based resist like Forbes, the ones with oil don't work nearly so well.
- Jeff Longtin and Roberta12
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There isn't a one size fits all type program for slow cooling. What works for one glaze won't necessarily give you the same results with another glazes. If the glaze is a high gloss one then slow cooling might not have any appreciable effect on it. If on the other hand it's one with fairly high amounts of one of the matting oxides (calcium, magnesium, alumina, strontium, barium, titanium or zinc) then slow cooling will more than likely have an effect. Getting the schedule is a bit of trial and error but a general starting place for a cone 6 glaze fire once it's reached it's top temperature could be 9999F to 1900F then ramping down at 150F an hour to 1400F then off. (9999F is basically putting the kiln in a freefall without getting an error message)
If you do a drop and hold schedule for healing pinholes and blisters then I would suggest dropping your peak temperature at a rate of 9999F to 100F below your top temperature then holding there for approx 20 minutes then proceed with the 9999F to 1900F then 150F down to 1400F then off.
If you find the glazes are too matte then increase the temperature it drops at (perhaps to 175F an hour) and/or raise the 1400F up and see how they turn out. If they are too glossy but might be matte with a slower cool (perhaps 125F and hour).
- Hulk, PeterH and nathanhinshaw
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@Jay Decker, Studio Potter magazine link to his article "Down the Spinal Canal" here. If that link doesn't work for you then try this one to see the article. Glicks article is towards the end of the issue. You can either do a paid option or a free one to read it.
Welcome to the forum.
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+1 for a fine mesh kyanite. @EarthToMatthew, good article on kyanite additions to clay below, worth a read to see if it sounds like what you are looking for.
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Quick comment about ^6 electric fired chun glazes and achieving a chun effect (that is to say a glaze that relies on a scattering of light to achieve a blue colour), it is going to be really difficult to achieve a true chun effect in an electric kiln at ^6. I haven't seen that glaze so I don't know how it compares to a high fire reduction chun. How close are the crazing lines with this glaze? (closer they are the more altering the glaze needs and/or might require so much changing that it won't really resemble the original glaze) BTW a really good article on Chun glazes and a recipe for a ^6 one here. Article is behind a paywall but you can access 3 free articles a month. I've posted the recipe from this article below, credit to Ryan Coppage and Ernestine Sitkiewicz. Do note that the clay used in Ernestine Chun is Laguna Frost which will take high expansion glazes well.
Second glaze, again, how bad is the crazing? If it isn't too bad I would look to increase the alumina and silica by a ratio of 1: 1.25 of epk : silica. See how high you can get the silica and alumina and still have a good melt then test for crazing. If that isn't enough I would be looking to lower the sodium and potassium and replace those fluxes by increasing the magnesium (from the talc) and probably adding some lithium (from spodumene). I would also be using 325 mesh silica in recipes. Have a look at some low expansion clear glaze recipes and see how the formula differs. You can get away with having higher boron that 0.15 if there is plenty of silica and alumina in the recipe and still have a durable glaze. Keep an eye on the silica:alumina ratio while you are tinkering with it.
Keep in mind that not all glazes can be adapted to fit all clay bodies. There are many glazes that need so much tinkering that the new glaze won't bear much resemblance to the original recipe. Also, the type of fluxes used have an effect on colourants, sometimes noticeably. As an example I'm guessing your ^6 electric chun recipe would give a turquoisey / aqua colour? In many other glazes copper will give a green.
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2 hours ago, Hulk said:
In my (limited) experience, calculated COE values are helpful to compare a glaze against a reformulation of the same glaze - where the ingredients are adjusted, and/or where a new ingredient is substituted in part.
+1 for this. COE values are extremely helpful when adjusting a glaze by increasing or decreasing one or more ingredients that already exist in the glaze. Throw in another material or look at a different glaze recipe and you now are working with an entirely different glaze with its own dynamics.
23 hours ago, Marilyn T said:2. I have successfully used glazes from COE( 5.9) Folk Art White to COE (7.3) Raw Sienna. The only one that has crazed on me in this range (when glazing both sides of the piece) was (6.82) Chun Celadon from the book Amazing Glaze. I did get some crazing on glazes at 6.52 (Glossy Base Glaze #1 from MC6) if I only glazed the outside. All of the successful glazes passed the usual hot water, oven, freezer tests but two of the bowls (one in Spearmint (6.8) and one in Powder blue (6.6)) didn't give a "ping" sound about one year after putting them into kitchen use even though there was no visible flaws. The rest of the ware in these glazes passed the "ping" test. My absorbancy tests range from .8 to 1.2%.
Can't just look at one number or range and expect all glaze formulas within that range to fit. In addition to the different oxides contributing different properties and melts you also have to look at the type of glaze it is in regards to both opacifiers, colourants and cooling.
If the Spearmint or any of the other glazes that are matte or semi-matte then COE numbers are not valid at all as some of the matting agents (like the calcium in Spearmint) will precipitate out the glassy matrix onto the surface of the glaze causing the semi / matte surface. By the calcium doing so you have created a microcrystalline glaze, COE calculation figures only work with a fully melted gloss glaze. Same reason why looking at a clay body recipe in glaze calc the COE figures means nothing given that clay is a crystalline material and not a fully melted gloss glaze.
Re colouring oxides and opacifiers. Some glaze materials, like zirconium, will give you a higher calculated COE figure but this is only looking at theory and not practice. In reality zirconium does not enter the melt therefore the change it imparts in the COE figure is skewed. Zirconium particles act like miniature boulders in the glaze and if a craze line starts the zirconium boulder stops the craze from propagating. Many colouring oxides and titanium / rutile will also decrease crazing. Boron is another good example of how glaze calc doesn't show the entire picture, in theory you could increase the boron to really lower a COE but in practice if you go beyond a certain point crazing will increase. I would suggest looking at the properties of each glaze material and what the contribute to the glaze, look at COE figures for each of the materials. If you see a formula with high amounts of sodium and or potassium chances are it's a high expansion glaze that will probably craze on a low expansion clay. Look for recipes with low expansion fluxes like magnesium, lithium, moderate amounts of calcium plus good levels of silica and alumina versus ones with higher expansion fluxes and low levels of silica and or alumina and for cone 6 boron around 0.15
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7 hours ago, Rae Reich said:
Never give your family pots you don’t care if you see again, unless they’re clumsy.
The pots or the family? Maybe both?
I have regretted selling a few pots. One was a sculpture I made in school, the other pots were all soda fired pots that I don't get the opportunity to make very often.
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14 hours ago, Kelly in AK said:
Wow! Look at that. Glazed vitreous ware at cone 03. I’m not seeing any obvious glaze defects, looks like your “low” bisque temperature isn’t causing problems. Cool!!!
+1
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Is it one of the controllers on page 7 of this link? http://www.ceradelindustries.com/fileadmin/download_en/ThermConcept-Kilns.pdf
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If you want something to use up the 60 mesh and you make anything with an unglazed gallery mixing the silicon carbide with toothpaste then using it as a grinding compound will make the unglazed rims or galleries as smooth as glass. A few blobs of the silicon carbide toothpaste around the rim then rotate the rim several times then rinse it off well, lids will fit really well and won't make that grinding sound when you put them on.
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I would go with E.
E - make a few test tiles and see which you prefer.
I would probably start with trying the white underglaze on greenware then red underglaze on top of that then bisque then glaze. (make sure each layer is dry before putting on the next) Is the underglaze compatible with the clear glaze? At the same time I would try the other options and see what happens. I'ld wrap up the piece (or put it in a ziploc if it fits) and wait until your tests are done. I know it can be tempting to just go for it but test tiles really are a good idea.
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On 1/21/2023 at 7:58 AM, Denice said:
I had a teacher that demonstrated throwing clay with broken flourescent bulbs in it.
On 1/22/2023 at 9:13 AM, Denice said:He had us find old bulbs and break them over a trash can outdoors because the powder in side of them was dangerous to breathe. We washed them and brought them to class,
Just in case someone thinks this would be something to try, apart from the obvious risks of cutting hands with broken glass there is also the hazard of mercury exposure from florescent bulbs. This practice is not recommended.
https://www.osha.gov/sites/default/files/publications/mercuryexposure_fluorescentbulbs_factsheet.pdf
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Hi Babs, sorry for the delay, hectic day.
I found my old glaze notes and the link below with a couple recipes I posted, don't know if you used one of those? I have about 10 pages of notes from back in 07-09 when I was using crawl glazes. I also asked a friend for her recipe which she shared, last one in these three.
From my notes these are the two I used the most:
Cone 6 Crawl - 1
Neph Sy 60
Ball clay 18 (I used om4 but most should work)
Magnesium Carb 22
Ferro 3134 6
106
Superpax 12
C9+ Crawl ^6 (another blended recipe, way to many ingredients but it worked)
Soda spar 15
Ferro 3134 19
Talc 5
EPK 10
Magnesium Carb 27.5
Neph Sy 12.5
Whiting 3
Ball Clay 5
Silica 4
101
Superpax 12
My friends recipe is a blend of a Brian Kemp Crawl and Mark Bell Crawl, she applies it underglazes and it always looks lovely. It's more melted than my chiclet one but not as melted as a brain crawl or beady eyes crawl.
^6 Crawl Kemp / Bell blend
Magnesium carb 30
Talc 9
Zinc 2
Ferro 3134 9
Soda spar 30
EPK 20
100
Is this the link to the original convo re crawl glazes you started? I posted a recipe in the thread below that is the same as the long one above (c9+) just totalled different.
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Do you have some test pieces with the same glaze on it? If not I would make a couple test pieces with some contours etc and try out experiments on those. Check out sand blasting services and or rentals.
Welcome to the forum. -
If you have access to sandblasting that should work.
Examples of Eric Rempe work and how he does it here. Would it be easier to remake the piece and use a less glossy glaze?
An experiment in Fritware Zero3
in Clay and Glaze Chemistry
Posted · Edited by Min
added a thought
Oolites then? But why would they be forming? Given the fibrous like structure of wollastonite is that acting like a seeding agent? Wonder what would happen if you used calcium carb to supply the calcium and adjusted the silica to balance if it would still happen? Is increased agitation contributing? hmmm, curious.
edit: another thought, slip with dry scrap vs slip without scrap added, is there a difference?