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Min
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Posts posted by Min
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2 hours ago, mr_glazy_man said:
The concept of “durability” is interesting to me - what aspects of durability are we talking about? Is it mostly related to food safety? Therefore, cutlery marking? Leachability? Or is it more about strength, dent resistance etc?
Durable glazes are those that can withstand abrasion from cutlery without scratching or marking and resist chemical attack. I haven't read about dent resistance of glazes but many people prefer glazes not to craze for functional ware.
I'm thinking that as far as your wall tiles go (good to know what you are making), the tile and glaze would break together with a heavy impact. I would imagine your abrasion resistance would be along the lines of what potters making functional ware would test for with cutlery. To increase the durability of a glaze having as much silica and alumina in the glaze as can be taken into a melt is important as is firing the glaze to maturity and not overloading the fluxes or colourants. Flux ratio might or might not make a difference for your purposes. I would do lots of testing of the glazes in the manner in which you would expect the tiles to be used. Cleaners used, brillo pads etc.
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If it's an old brush on glaze, from Amaco:
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Interesting! Would also be interesting to see what happens to fire it in your new kiln under reduction, depending on how hot you get there might be nothing but some of the iron left. Maybe fused a bit with whatever it's being fired on?
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If the glaze doesn't need to be durable it opens up a lot of possibilities, even using a raku crackle glaze. Thing with Stull charts and crazing it doesn't take into account different claybodies or firing cone. Looking forward to seeing your results.
If you have ferro 3134 you could use that to supply boron with the 3110 and 3195. I did a quick example one below, if it's too runny you should be able to add up to 5 more epk and still have a good crackle / craze.
Flux ratio is 0.4:0.6 LOI is only 1.0 so it should have very little micro-bubbles and be very clear. Could be really runny so if you test it fire on a waster.
Something like this
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12 hours ago, TaraB said:
My question is why would these be non vitrified if the correct cone was used and the sitter dropped at the right temp?
Like others have said, it's the firing of the clay temp.
Say you are baking chocolate chip cookies and the recipe says you can bake them to 300F or you can bake it to 400F, does that make sense? Can the cookies be baked through at both temperatures?
Back to your clay, if you are making items not meant to hold liquids and you don't mind them absorbing water then firing to the lower cone might make the clay mature enough for those purposes. But a clay can't be as vitrified as possible at two different ranges. If it is a midfire clay and you fire to highfire then chances are it will have bloating, slumping, brittleness, etc issues. If you on the otherhand fire a highfire clay to a lower range then chances are it won't be as mature as possible and will be immature and underfired. In other words it won't be as strong, will be under vitrified, likely leak and absorb water. This is a problem for functional wares that are meant to hold liquids or will be washed more than a few times. Pots will absorb water which will induce crazing, leak, get hot in the microwave, grow mildew / mold etc.
Another thing I would look at is your glaze maturing temperature, is it under-fired too? What is the recommended cone for it? If your glaze is a cone 10 glaze then the mugs you currently have could be re-fired to just under that (given they already have had a lot of heatwork). Lustre will burn off and probably leave a purple mark but you might be able to save them. Leave the mugs that had liquid in them to dry in a 200F oven overnight to dry them out before firing them and I'ld suggest firing them on waster slabs in case the glaze runs. Nothing to loose.
Going forward look for a body that matures at the same cone as what you are firing to. Testing your claybody can be done quickly or in a more detailed method, I'ld suggest the more detailed method whenever you test a new clay. Link here if you need it on how to do so.
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@Tina01, I think you need to decide if you want to try and fix your current clay or try and find a new supplier who can sell you a ready to work with clay for your chosen firing range.
If you decide to try and rescue your current clay it's likely you will have to test and modify every batch. I'm guessing you are a new potter and while fixing your current clay is probably doable I would suggest removing this obstacle from your path of learning to make pots, might make the journey easier at this point.
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@suetectic, we do go off on tangents on the forum but at the risk of hijacking the initial thread its best to try to keep them short. Can't know in advance how off topic a thread will go but at this point it would be best to start a new thread with your temper definition question if it's going to go any further. thanks
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I'ld suggest getting the boron up to 0.50
Calcium carb and dolomite are not the greatest fluxes for lowfire so it's going to take more boron than you have to get a good melt. I don't know what the application of the tiles will be, if you can sacrifice some durability the flux ratio doesn't have to be in the 0.3:0.7 range.
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I suggested some magnesium to get the flux ratio into a good range, could use calcium instead. Yes, fritted form of magnesium would enter the melt easier than dolomite or talc but magnesium frits are super expensive, at least where I live. The amount you need shouldn't be much, can still have a high expansion crazed / crackle glaze with a little magnesium in the recipe. If you can make a balanced recipe using all frits plus a bit of clay to keep things somewhat suspended that would melt the best. If you don't have access to the COE figures on Glazy then post your potential recipe(s) here and I'll run them through Insight for you. Keep the sodium and potassium high.
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@Jeff Longtin or @Mark C. (if you are back home again) can you help with this question?
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On 10/29/2022 at 8:26 AM, Hulk said:
Isn't Georgia known for white clay?
Perhaps pottery shops in Georgia could direct you to suppliers.
Some may carry supplies! For example, the MODI Ceramic Project in Tbilisi, who feature Seramiksir products
MODI ceramic shopThis shop's website mentions Georgian white clay, " The business prides itself on being the first studio to develop and produce the acclaimed Georgian porcelain..."
About us – White Studio
Here's a listing of global suppliers, interesting!
Ceramic Materials Suppliers — pottery to the peopleI found a potter in Georgia that might be able to help if Tina is looking for a Georgian contact, perhaps this fellow could help with where he gets his clay or materials from: https://www.homofaber.com/en/discover/discover-gigisha-pachkoria# .
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15 hours ago, mr_glazy_man said:
Doing a bit of research on Digital Fire suggests that 3110 is a very low melting frit. I combined it with 10% EPK (the classic 90% frit, 10% clay combo) and test fire across these temperatures at five temperature points between 935C - 1110C.
I couldn't get it to nicely melt until it hit 1080; any lower was extremely underfired. Moreover, punching this into the Glazy calc does indeed suggest that it is *almost* underfired.
Can't take any frit and add 10% epk and expect it to work.
Have a look at boron levels in the unity formula, need to have the boron for a ^05 - 04 glaze at least around 0.50 to melt properly. 90 ferro frit 3110 + 10 epk will give you a boron level of 0.10 (unity formula using Insight glaze calc). This is low even for a cone 6 glaze, let alone a lowfire one.
Work on getting the boron up to the 0.50 range. If you go really far above this you will likely get boron clouding, this might not be an issue, depends if you want a clear crackle/crazed glaze. I'ld suggest trying ferro frit 3195 + ferro frit 3110 + epk + dolomite (if you have it, talc if not). Play around with those 4 materials on Glazy, you should be able to get 4 points covered: adequate boron levels, adequate silica and alumina, flux ratio at the 0.3:0.7 ratio plus a high expansion to cause the crazing.
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@caveman, might be best to start a new thread with your pit firing with fire bricks and your wild clay tiles.
- Pres and Kelly in AK
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41 minutes ago, suetectic said:
I should have probably suggested previously that temper 'also' includes to help indicate temper includes refractory and non-refractory material.
I would suggest that the definition of temper would also include organic and inorganic materials. Grog could be further defined as to being soft grog (not vitrified) vs vitrified. Also whether the word temper is used as a noun or a verb.
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6 hours ago, mr_glazy_man said:
I want to get this glaze to melt glossy at around 05. My instinct is to pair it with 3195 for the melting power of higher Boron, but 3195 is also a higher (relatively speaking) magnesium frit and will likely reverse the crazing via COE alteration.
Ferro frit 3195 does't contain magnesium. It contains SiO2, Al2O3, B2O3, CaO, and Na2O. Ferro frit 3249 is a good one to supply magnesium if that's what you are looking for.
Are you looking for a crazed / crackle ^05 glaze for non functional work?
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If you want a rabbit hole this page has 3 to go down. Tantalizing picture of a similar glaze on the Glazy page. All 3 links are working, papers by Dorothy Bassett.
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29 minutes ago, Flammingo Studio said:
I checked mine, several times over, and 100ml weights 95 grams.
With all due respect it can't be 95 grams. 100ml of water weighs 100 grams. Every material added to the water in casting slip has a higher specific gravity than water. Your friends 1.75 makes sense, perhaps they could use their scales for you and weigh some out?
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Hi and welcome to the forum!
I would start by measuring the specific gravity of the casting slip with an accurate scale. Should be somewhere between 1.72 and 1.80. If it's below 1.72 I would let some of the water evaporate off it until it's in that range and try casting with it again. If you stir it up with your hand does it web between your fingers for a few seconds when you take your hand out the slip and spread your fingers apart? Doesn't need to be as much as this but similar too.
Couple questions, is the shop owner the person who made the casting slip or is if from a different manufacturer that you could contact? If so ask which talc they are now using in it and what specific gravity they recommend.
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17 minutes ago, PeterH said:
I have a faint memory of stale 7-up being used as a medium by some Japanese potters.
OILS AND MEDIUMS http://www.porcelainpainters.com/mediums.htm
Sugar
There are numerous recipes for sugar solutions to be used for pen work and for painting. The most common and easy medium is regular 7-Up. Everyone who paints or draws with sugar solutions seem to have their favorite mixture. The most common recipe is made by boiling 2 parts water with 1 part sugar, and using the syrup as a painting medium or thinned for pen work. It dries quickly and requires practice to gain consistency in brush work.Is the op painting on fired glaze or under and over unfired glaze? I read their post as unfired.
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Hi and welcome to the forum!
There are a number of threads discussing HEPA filters on the forum. If you do a search on the main page links will come up. The air filter you linked to is mentioned in this thread. Many potters work from their homes and keep dust to a minimum by diligent wet mopping and sponging down surfaces before the dust has time to accumulate.
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Just in case you haven't seen them already, Paul Lewing article here, (link should work, let me know if it doesn't). Another Lewing article on brushes here. He has also done a CLAYfliks video, that is behind a paywall but snippet below. Video covers basic concepts, surfaces to paint, tools and mediums, some examples of working etc.
New Directions in China Painting with Paul Lewing
Welcome to the forum!
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On 10/27/2022 at 11:43 AM, TasseCeramics said:
Also does anyone know of any kilns in the Derby area I can fire my things in?
I've never used this service but it might be helpful. Kiln Share has some in the general area but not Derby specifically.
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Hi and welcome to the forum!
Ceramic stilts work well for things like this. They leave a little glaze prickle on the underside but those can be carefully ground down. Some clays will slump enough for these not to work, will have to try and see with a waster piece of clay underneath in case it sags onto the kiln shelf.
- freckldceramics, Rae Reich and Chilly
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@Pir, looks like you already have a couple frits that contain boron, ferro 3134 and ferro 3195. Given that it's the boron you will be using a frit to replace the gerstley borate with just use what you have, can make the formula work with either.
Re my comment about might needing to add bentonite, look at the screenshot below, original is first recipe Jack's Green Matte, with ferro 3134 altered 1 and with ferro 3195 altered 2. See how little clay there is if you use ferro 3195, it's just at 6.33, this would be a good example of why bentonite would be needed. Using ferro 3134 gets the clay up to almost 16 therefore no bentonite needed in that version. Tiny differences from the original to the others, don't think they are significant in any way.
Wild Clay Processing
in Clay and Glaze Chemistry
Posted
Starting a pinned thread on testing and working with wild clay as there seems to be a fair bit of interest in this.
Few links discussing this below, please feel free to add info and experiences using wild or found clay.
https://digitalfire.com/article/how+to+find+and+test+your+own+native+clays
https://www.leelachakravarti.com/blog/wild-clay-top-tips-for-making-pottery
https://ceramicartsnetwork.org/ceramics-monthly/ceramics-monthly-article/wild-clay-and-glaze (this one is behind a paywall but you can see 3 articles a month for free)