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Min

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  1. Like
    Min got a reaction from Kelly in AK in Chrome & Zinc - toxic?   
    Let's not throw the baby out with the bathwater here. The form of chrome used makes all the difference in the world in regards to toxicity.
    Potters use chrome oxide, it is insoluble in water and gets bound in the glaze matrix in a balance glaze. It is volatile in the kiln so it can cause a pink blush on tin white glazes. Wear gloves if you get contact dermatitis with it. (it's a good idea to wear gloves whenever handling raw materials and glaze slurries to avoid skin reactions)
    We do not use the exceedingly dangerous hexavalent chromium in ceramics. Iron chromate is toxic, stay away from using it.
    Zinc oxide fumes from kiln firing shouldn't be breathed in, zinc can become volatile above around 850C/1560F and like all the materials we use in glazes practice good studio hygiene and wear a respirator while handling dry materials. In a glaze it isn't a problem. 
    Chrome + tin pinks and reds are perfectly safe, whether in a stain or from the oxides.
     
     
     
  2. Like
    Min got a reaction from Pres in QotW: Where and how do you store your clay?   
    I prefer throwing soft clay and more often than not my clay is too firm so my go to storage is to first  pile boxes of clay in the corner of a hallway. I open the bags up and add a bit of water, do them back up and let them sit in a large rubbermaid bin filled with water for at least a few days,  I add more of bags of clay into the water filled bin as I use them up.
  3. Like
    Min got a reaction from Callie Beller Diesel in Strontium Crystal Magic Cool- Food Safe?   
    I prefer to use the term "durable" rather than food safe when talking about glazes. There isn't one agreed upon definition of what makes a glaze "food safe". In North America if a glaze does not contain lead or cadmium it can be labelled food safe. This is a very wide definition and adding something along the lines of what Mayco says "Finishedware producers bear responsibility for food safe testing their ware being sold into commerce." IMHO isn't good enough. Like Callie said Strontium Crystal Magic (SCM) is  fine on the outside of pots where your mouth or food won't be in contact with it.
    Re lithium and toxicity, just adding a little bit. Topic of lithium and toxicity has come up in many discussions in many forums etc over the years. My impression of the reading I've done is it might not be an issue for most people but for those on lithium therapy it can be, both in the process of mixing glazes and leaching glazes.  Poison is in the dosage scenario.
    With all due respect to Callie I found SCM quite rough, dry and unmelted. You could try it by itself on a test tile and see how you find it but it's a bit of a moot point because it isn't used by itself.  The overload of titanium is what makes the crystals/variegation when layered with other glazes. A good way to get interesting glaze reactions is to layer 2 or more dissimilar glazes, what one glaze lacks or has a surplus of reacts with the other glaze, this often results in interesting visual texture. SCM is loaded with fluxes to react with other glazes, that's part of the reason why it works.
    Re silica and glaze durability, having as much silica and alumina in a glaze is one of the ways to ensure a durable glaze.  For cone 6 having at least 2.5 molar of silica is a good starting place, if the glaze can dissolve more then it's a good idea to add it if you are looking for a durable glaze. If you look at the screenshot above in the bottom half of the image you can see the silica is 1.68 so at the bare minimum it is about 1/3 short of where it should be. Overloading a matte glaze can quite often turn it into a gloss glaze  and really oversupplying it can turn it back into a matte and crazed glaze so there are parameters within which to work. 
    Another aspect of silica that is often overlooked is the mesh size of the silica being used. When you mix glazes using a 325 mesh size silica more of the silica will likely be dissolved in the glaze than if you use 200 mesh. (not applicable for the SCM)
    One more thing is to look at the colouring oxides used. Don't use crazy amounts of colouring/transition oxides, use the least you can to still achieve the effect/colour you are after.
    There is a good article on toxicity that includes materials here if it helps.
  4. Like
    Min got a reaction from dhPotter in Strontium Crystal Magic Cool- Food Safe?   
    I prefer to use the term "durable" rather than food safe when talking about glazes. There isn't one agreed upon definition of what makes a glaze "food safe". In North America if a glaze does not contain lead or cadmium it can be labelled food safe. This is a very wide definition and adding something along the lines of what Mayco says "Finishedware producers bear responsibility for food safe testing their ware being sold into commerce." IMHO isn't good enough. Like Callie said Strontium Crystal Magic (SCM) is  fine on the outside of pots where your mouth or food won't be in contact with it.
    Re lithium and toxicity, just adding a little bit. Topic of lithium and toxicity has come up in many discussions in many forums etc over the years. My impression of the reading I've done is it might not be an issue for most people but for those on lithium therapy it can be, both in the process of mixing glazes and leaching glazes.  Poison is in the dosage scenario.
    With all due respect to Callie I found SCM quite rough, dry and unmelted. You could try it by itself on a test tile and see how you find it but it's a bit of a moot point because it isn't used by itself.  The overload of titanium is what makes the crystals/variegation when layered with other glazes. A good way to get interesting glaze reactions is to layer 2 or more dissimilar glazes, what one glaze lacks or has a surplus of reacts with the other glaze, this often results in interesting visual texture. SCM is loaded with fluxes to react with other glazes, that's part of the reason why it works.
    Re silica and glaze durability, having as much silica and alumina in a glaze is one of the ways to ensure a durable glaze.  For cone 6 having at least 2.5 molar of silica is a good starting place, if the glaze can dissolve more then it's a good idea to add it if you are looking for a durable glaze. If you look at the screenshot above in the bottom half of the image you can see the silica is 1.68 so at the bare minimum it is about 1/3 short of where it should be. Overloading a matte glaze can quite often turn it into a gloss glaze  and really oversupplying it can turn it back into a matte and crazed glaze so there are parameters within which to work. 
    Another aspect of silica that is often overlooked is the mesh size of the silica being used. When you mix glazes using a 325 mesh size silica more of the silica will likely be dissolved in the glaze than if you use 200 mesh. (not applicable for the SCM)
    One more thing is to look at the colouring oxides used. Don't use crazy amounts of colouring/transition oxides, use the least you can to still achieve the effect/colour you are after.
    There is a good article on toxicity that includes materials here if it helps.
  5. Like
    Min got a reaction from dhPotter in Strontium Crystal Magic Cool- Food Safe?   
    First off have a look at the materials and their amounts in the recipe itself. I re-totalled the recipe from the original 60.60 to 100 as that is the standard base amount. When we apply a standard amount it makes it easier to notice possible areas of concern. Top part of the screenshot below is the Glazy recipe re-totalled to 100.
    First thing that jumps out is there is no silica added to the recipe. Yes, there will be silica in the formula from the feldspar etc but probably not enough. (more on this later) Second thing that jumps out is the amount of titanium in the recipe, nearly 12%, this is a huge amount! Third thing, is approx 40% feldspar for a ^6 glaze is getting quite high. Put these things together and you have a recipe that won't be durable (low silica), probably won't melt properly at cone 6 and is overloaded with titanium.
    I know this glaze and the "warm" version of it are very popular at cone 6. It's important to note also that it isn't used as a standalone glaze, it is used as a layering glaze with one or more other glazes. What the combined chemistry is of the layered glaze is what needs to be looked at, will those be durable, I don't know, each combination would need to be looked at.
    BTW, giving credit where credit is due, this glaze started off as a Tom and Elaine Coleman ^10 glaze called Yellow Crystal Matte. Barium was removed from original glaze and strontium subbed for it, the gerstley borate was subbed with the Ferro 3124 and the zinc removed.
     

     
  6. Like
    Min got a reaction from Hulk in Strontium Crystal Magic Cool- Food Safe?   
    I prefer to use the term "durable" rather than food safe when talking about glazes. There isn't one agreed upon definition of what makes a glaze "food safe". In North America if a glaze does not contain lead or cadmium it can be labelled food safe. This is a very wide definition and adding something along the lines of what Mayco says "Finishedware producers bear responsibility for food safe testing their ware being sold into commerce." IMHO isn't good enough. Like Callie said Strontium Crystal Magic (SCM) is  fine on the outside of pots where your mouth or food won't be in contact with it.
    Re lithium and toxicity, just adding a little bit. Topic of lithium and toxicity has come up in many discussions in many forums etc over the years. My impression of the reading I've done is it might not be an issue for most people but for those on lithium therapy it can be, both in the process of mixing glazes and leaching glazes.  Poison is in the dosage scenario.
    With all due respect to Callie I found SCM quite rough, dry and unmelted. You could try it by itself on a test tile and see how you find it but it's a bit of a moot point because it isn't used by itself.  The overload of titanium is what makes the crystals/variegation when layered with other glazes. A good way to get interesting glaze reactions is to layer 2 or more dissimilar glazes, what one glaze lacks or has a surplus of reacts with the other glaze, this often results in interesting visual texture. SCM is loaded with fluxes to react with other glazes, that's part of the reason why it works.
    Re silica and glaze durability, having as much silica and alumina in a glaze is one of the ways to ensure a durable glaze.  For cone 6 having at least 2.5 molar of silica is a good starting place, if the glaze can dissolve more then it's a good idea to add it if you are looking for a durable glaze. If you look at the screenshot above in the bottom half of the image you can see the silica is 1.68 so at the bare minimum it is about 1/3 short of where it should be. Overloading a matte glaze can quite often turn it into a gloss glaze  and really oversupplying it can turn it back into a matte and crazed glaze so there are parameters within which to work. 
    Another aspect of silica that is often overlooked is the mesh size of the silica being used. When you mix glazes using a 325 mesh size silica more of the silica will likely be dissolved in the glaze than if you use 200 mesh. (not applicable for the SCM)
    One more thing is to look at the colouring oxides used. Don't use crazy amounts of colouring/transition oxides, use the least you can to still achieve the effect/colour you are after.
    There is a good article on toxicity that includes materials here if it helps.
  7. Like
    Min got a reaction from Callie Beller Diesel in Seams on slab-made vessels   
    Copying a design versus using the same technique while making a pot are two different things. Are there any new designs in functional ware that haven't been done before by someone somewhere, I don't know but I sort of doubt it.
    I have noticed quite a few makers doing exactly what you describe; leaving the mark of the making process visible at the joins. I don't think you need to waste your energy trying to justify your work. Getting inspiration from others work is one way to challenge yourself into making new forms, and making them your own.  I'm sorry you are going through this, it must have been upsetting to you.
  8. Like
    Min got a reaction from Callie Beller Diesel in Pinhole problems   
    No worries on firing when it's 40F outside.
    If the glaze crazes when you remove pots from the kiln it won't be because of the temperature being a little cold. It will be because the glaze is too small for the clay. Simple way to think of this is to think of a pair of jeans and how they fit. If I wear a size 10 and my daughter wears a size 4 if I put her jeans on the seams will split. If she puts my jeans on they will bag out and fall off. Tight splitting jeans is like a crazing glaze, loose falling off jeans is like shivering glaze. Crazing is far far more common than shivering. 
  9. Like
    Min got a reaction from Callie Beller Diesel in Pinhole problems   
    I think that since so many of us fire to midrange the go to mindset is bisque low, fire higher to glaze. Problem with this when working with earthenware is more often than not the commercial glazes are rated in the 06-04 range yet many earthenware bodies will actually mature higher than this and still be porous enough to take glaze well. I haven't used the body in question, but if it can go to 02 (as the lit suggests) then I would at least try 03 and see how it does. 
  10. Like
    Min reacted to PeterH in Dry Effect Oxide Patina   
    It sounds like they are a special case of  "oxide washes".  (Which may be a productive search term.)
    https://www.vincepitelka.com/wp-content/uploads/2016/03/Surface-Design-Patinas-and-Glazes.pdf
    Dry-Effect Oxide Patinas
    An interesting category of patinas are those which simply approximate the accumulation of dirt and debris found in much ancient claywork. Varying proportions of zircon opacifier or tin oxide and coloring oxides with some 3134 frit (to flux the patina onto the surface) will give a range of “dirt” colors from very light to dark brown or black.
    https://ceramicartsnetwork.org/pottery-making-illustrated/pottery-making-illustrated-article/In-the-Studio-Washes-and-Patinas#
    In the Studio: Washes and Patinas
    Gerstley or Gillespie borate, Ferro frits 3110 or 3124, borax, or any other flux-based material can be used in combination with colorants to create patinas.
    ... so I think the message is to use a flux appropriate for your firing temperature.
    If you say what cone/temperature you fire to an expert will probably chip in with a recommendation (or confirmation that 3134 is OK).
  11. Like
    Min got a reaction from Babs in Strontium Crystal Magic Cool- Food Safe?   
    First off have a look at the materials and their amounts in the recipe itself. I re-totalled the recipe from the original 60.60 to 100 as that is the standard base amount. When we apply a standard amount it makes it easier to notice possible areas of concern. Top part of the screenshot below is the Glazy recipe re-totalled to 100.
    First thing that jumps out is there is no silica added to the recipe. Yes, there will be silica in the formula from the feldspar etc but probably not enough. (more on this later) Second thing that jumps out is the amount of titanium in the recipe, nearly 12%, this is a huge amount! Third thing, is approx 40% feldspar for a ^6 glaze is getting quite high. Put these things together and you have a recipe that won't be durable (low silica), probably won't melt properly at cone 6 and is overloaded with titanium.
    I know this glaze and the "warm" version of it are very popular at cone 6. It's important to note also that it isn't used as a standalone glaze, it is used as a layering glaze with one or more other glazes. What the combined chemistry is of the layered glaze is what needs to be looked at, will those be durable, I don't know, each combination would need to be looked at.
    BTW, giving credit where credit is due, this glaze started off as a Tom and Elaine Coleman ^10 glaze called Yellow Crystal Matte. Barium was removed from original glaze and strontium subbed for it, the gerstley borate was subbed with the Ferro 3124 and the zinc removed.
     

     
  12. Like
    Min got a reaction from Roberta12 in Seams on slab-made vessels   
    Copying a design versus using the same technique while making a pot are two different things. Are there any new designs in functional ware that haven't been done before by someone somewhere, I don't know but I sort of doubt it.
    I have noticed quite a few makers doing exactly what you describe; leaving the mark of the making process visible at the joins. I don't think you need to waste your energy trying to justify your work. Getting inspiration from others work is one way to challenge yourself into making new forms, and making them your own.  I'm sorry you are going through this, it must have been upsetting to you.
  13. Like
    Min got a reaction from Pres in Seams on slab-made vessels   
    Copying a design versus using the same technique while making a pot are two different things. Are there any new designs in functional ware that haven't been done before by someone somewhere, I don't know but I sort of doubt it.
    I have noticed quite a few makers doing exactly what you describe; leaving the mark of the making process visible at the joins. I don't think you need to waste your energy trying to justify your work. Getting inspiration from others work is one way to challenge yourself into making new forms, and making them your own.  I'm sorry you are going through this, it must have been upsetting to you.
  14. Like
    Min got a reaction from Bill Kielb in Clear glaze looks yellow   
    Hi and welcome to the forum.
    From Standard's website and their  Lowfire Slip page there is a link with glaze recommendations. Duncan IN1001 "slightly yellow, may blur crisp underglaze lines". There are four other Mayco glaze result descriptions there also. It seems the least yellowing recommendation is Spectrum 700. Standard recommends doing both bisque and glaze to cone 04.
    Link here: https://cdn.shopify.com/s/files/1/0039/8177/0841/files/105-LFW_Glaze_Rec.pdf?v=1674848426
  15. Like
    Min got a reaction from Hulk in Clear glaze looks yellow   
    Hi and welcome to the forum.
    From Standard's website and their  Lowfire Slip page there is a link with glaze recommendations. Duncan IN1001 "slightly yellow, may blur crisp underglaze lines". There are four other Mayco glaze result descriptions there also. It seems the least yellowing recommendation is Spectrum 700. Standard recommends doing both bisque and glaze to cone 04.
    Link here: https://cdn.shopify.com/s/files/1/0039/8177/0841/files/105-LFW_Glaze_Rec.pdf?v=1674848426
  16. Like
    Min got a reaction from Hyn Patty in Cracks when double-bisquing large work ?   
    Slow. Both for firing up and cooling down.
    These pictures are from Digitalfire of lowfire ware, pots have cracked from uneven cooling, edges will have cooled faster than the middle area of the pieces. The way to avoid this is to have the cooling down go as evenly as possible. Slow the cooling down between 1150F - 950F, I go at 100F/hour through this zone with suspect work.

     There is negligible shrinkage, ie less than 1% between bone dry greenware and bisque firing to ^06- ^04, would be interesting to see data that shows refiring to a lower temp causes more shrinkage.
    edit: when having your piece in the kiln put it between shelves, not at the top or bottom of the kiln, this helps the heat even out also. I put rectangular or triangular kiln posts around the outside edge of the shelf also. (round posts can roll)
     
  17. Like
    Min got a reaction from LeeU in Seams on slab-made vessels   
    Copying a design versus using the same technique while making a pot are two different things. Are there any new designs in functional ware that haven't been done before by someone somewhere, I don't know but I sort of doubt it.
    I have noticed quite a few makers doing exactly what you describe; leaving the mark of the making process visible at the joins. I don't think you need to waste your energy trying to justify your work. Getting inspiration from others work is one way to challenge yourself into making new forms, and making them your own.  I'm sorry you are going through this, it must have been upsetting to you.
  18. Like
    Min reacted to Callie Beller Diesel in Can you predict the approximate drop/hold temperature in a drop and hold firing from the chemistry of a glaze?   
    This. 100000X this. If your clay body is giving pinholes of some kind with several glazes, it’s the clay body, not the glaze or the assorted firing cycles. It may well be that an ingredient in the Laguna body just doesn’t want to play nice, whatever is done with it. You have to weigh wether you like using this clay more than you want a perfectly defect free surface.
    If you need a good red clay/white glaze combo, M390 and Ravenscrag slip 80/20  with frit 3134, and 2 opacifiers of your choice. (I recommend a tin and zircopax combo if you don’t want any titanium variegation). Reasoning: they give different qualities of white. Tin by itself is very soft, and can be grey-ish or even drift towards a violet in certain light when used on M390 in particular. It’s also expensive. Zircopax by itself is very stark, and gives a very “bathroom fixture” white that resists breaking or pooling. The 2 together give a soft white without weird tonal casts, gives a little more visual interest and offsets the end price of the glaze. I use a max of 10% opacifier, but judging from the look of your photos, you might want a slightly more translucent version, so you could see what happens with 7 or 8%. 
    I fire with a very analog kiln at home, so I can’t give specific numbers on ramps and speed. I slow my kiln down around the carbon burnout stages mentioned in the Steve Davis article, and I judge that through the colour of the kiln. I’ve recently started working at a place that has brand new Bartlett 2 touchscreens though. I feel spoiled! They are to be preferred over my methods.
    I think speed of bisque is more important than end temperature, so slow through the appropriate zones. I think the Naomi Clement one is a bit of overkill.  The 12-14 hours of Davis’s cycle (assuming no drying soak at the beginning) is plenty long. Note the pauses around 1500F that both Clement and Hulk have suggested.
    The glaze cycle I use to get what is effectively cone 7 is a drop and hold, similar to what you’ve already worked out. I go to cone 6 with a 20 minute hold after the drop.
    Note that there will be upcoming changes to M390: according to my supplier, Plainsman demand has gone through the roof lately, and they’re struggling to keep up. They have one clay mixer that they have to cycle all their different clay bodies through from lightest to darkest. While another one has been ordered, it’s not expected in until next year. In the meantime, they’ve made the decision to remove the 80 mesh sieve from the machinery in order to get the clay to go through faster. This will affect M390’s texture starting this year. So we’ll all have to revise some porosity testing until they get the new machinery in place.
     
    The last suggestion I would have is another bisque cycle. But this time, only go to 010. There have been a few reliable potters in various internet spaces lately speaking about this (For Flux Sake podcast in particular). I believe the argument is that the application a more porous clay body gives a dipped glaze results in fewer defects. I haven’t experimented with this personally though, so that one is a shot in the dark if nothing else works.
  19. Like
    Min got a reaction from Callie Beller Diesel in Can you predict the approximate drop/hold temperature in a drop and hold firing from the chemistry of a glaze?   
    Tagging @Callie Beller Diesel on this in case I'm misremembering but I believe she fires 390 to cone 7 for absorption reasons.
  20. Like
    Min reacted to Marilyn T in Can you predict the approximate drop/hold temperature in a drop and hold firing from the chemistry of a glaze?   
    I have attempted to contact Laguna twice before about a different clay (Laguna 65) and received a reply that they were forwarding my question to someone else -- never heard back.   So I probably won't contact them again.  
    I recently purchased a box of M390 and threw some test bowls.  I am including them in my next series of tests to see what the results are -- figured if Tony had success on M390 with the glaze G 3806 that I could use that as a comparison for the results on the Laguna 613 and go from there.  He uses the C6DHSC firing schedule so if I don't have good results on the  M390 it will indicate that something else is going on that I haven't thought about.   As part of covering all the bases I'm bisquing a few bowls at ^02 for comparison. Going to give the Laguna clay about another 2 weeks to reveal its mysteries then abandon ship (I only have 6 bags left).   -- 6 more glaze  firings to go (the golf course is calling!)  
    The good thing is that I am really good at throwing test bowls now.    
  21. Like
    Min reacted to PeterH in Tips for multiple coats of paperclay slip   
    Loosely related

     
  22. Like
    Min got a reaction from Rae Reich in QotW: Large or Small, creamed , slurry or water to lube your throwing?   
    750 ml yogurt container, so I guess that would be nearly as small as the paint cups with the handle. It sits in the splash tray (Bailey wheel), don't keep any sponges or chamois in it. I start with warm water then top it up as the day goes along. After a few throwing days I put it to one side, stir a splash or two of peroxide and then it goes into the reclaim.  3 yogurt containers used in rotation. 
  23. Like
    Min reacted to Bill Kielb in FtL/fired too long error message. Restart or not?   
    FTL message usually indicates not enough power to get to temp. Worn element(s), bad relay - some mechanical or electrical reason it cannot maintain a reasonable rate of heating at the end. On the test tile side, Orton says most of the important (flux) heat work work will be done in the last 200-250f degrees given a reasonable rate of rise during this period. If your kiln stops well short of that last 200-250 degrees then generally things can be restarted as if nothing significant happened. 
    In your case, you are sort of close so restarting likely fine if you can make temp at a reasonable rate. If it stalls again though you are going to need to diagnose the problem and those tiles are likely half baked and depending on the stall temp can end up looking any number of ways. If you have witness cones in place then plus one - you will have an idea of how much heatwork you achieved. If virtually none, then repair the kiln and refine.
    My guess is it stalled for a reason and It will stall again. My rule of thumb is if it stops 250f or more before it’s final temp it usually can be cooled and refired after repairs with it likely ending up looking / firing as normal. In effect no heatwork was done during the most important phase.
  24. Like
    Min got a reaction from Hulk in QotW: Large or Small, creamed , slurry or water to lube your throwing?   
    750 ml yogurt container, so I guess that would be nearly as small as the paint cups with the handle. It sits in the splash tray (Bailey wheel), don't keep any sponges or chamois in it. I start with warm water then top it up as the day goes along. After a few throwing days I put it to one side, stir a splash or two of peroxide and then it goes into the reclaim.  3 yogurt containers used in rotation. 
  25. Like
    Min reacted to Michelle Stroud Ceramics in What's up with Dolan Tools?   
    Spent some time chatting with Susan Dolan at NCECA this past weekend. First of all, she’s lovely, and cares deeply about creating quality tools. She was extraordinarily helpful in guiding me to which tools would work best for me and my work.  She knows it’s hard to get her tools, but she’s literally a one woman show. Her focus is so much on making, she chose not to have a booth and was set up with Clay Planet. Fortunately, she brought some pieces with her, and I was able to pick up 8 new tools (Lucky me!).  I don’t know if she had stock left over at the end of the show, but I’d look at Clay Planet first to see if they have any stock.  I don’t think Dolan is selling from their website, but prefer for a select group of distributors to manage that end so they can keep the focus on making. Hope that helps!! 
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