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PeterH

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  1. Like
    PeterH reacted to neilestrick in Underglaze Bleeding Wanted!   
    I follow a number of people on Instagram who use bleeding underglaze, and I've never seen them making it bleed in the raw stage. It's always the glaze causing the bleed. I can control the degree of bleeding on my work by simply making the glaze more or less fluid.
  2. Like
    PeterH reacted to Min in Underglaze Bleeding Wanted!   
    I've got a girlfriend who has signed up for a Dawn Candy workshop, on the materials list she said she uses Amaco Velvets but can use other brands. Sean O'Connel's website has the glaze recipe he uses from 2018 as Campana Clear. I've tested that glaze, it is fluid.  (contains zinc so chrome green stains in green underglazes are going to go muddy)
  3. Like
    PeterH reacted to tinbucket in Underglaze Bleeding Wanted!   
    If you notice both examples of running/bleeding you posted are blue, most likely a cobalt (carbonate or oxide) wash rather than an underglaze. If you are after blue, I would use a cobalt wash rather than underglaze. Unless it is very thinly applied, cobalt will have a tendency to run or bleed. 
  4. Like
    PeterH reacted to Eyvind in Using Tile Extruder Machine (Peter Pugger)   
    Here is the method I devised on offloading extruded clay ribbons and then cutting them. I was amazed and dismayed when I bought the pugger/extruder that so little practical information exists for this necessary operation.
    First, I did buy the PP manual tile cutting table. It had a wooden surface then: they have since changed to some synthetic resin or plastic. It also has some pizza cutter blades attached to a spindle that you can use: see their website. This is all gravy. What you need is a table the same height as your ribbon of extruded clay, or just a bit lower, with a relatively smooth surface.
    Wet clay sticks to everything. So I use a strip of window screening material as the underlayment. These strips are 12" wide by 4 feet long. I start the extrusion and immediately place the leading edge of the clay on top of the the 12" wide leading edge of the screen. The clay and screen attach and then about 4 feet of clay can run out onto the table, made "slick" by the use of the underlying strip of window screen. When the strip of screen is all used, I stop the PP, cut off the strip, and process the ribbon of clay. Because it is on a solid surface table, it can be smoothed, cut, stamped, etc just fine. The pizza cutter with an oil coating is the best straight-line cutter: it doesn't make a messy edge like a needle tool but it does create a slight gap (a "kerf") between tiles that prevents the wet clay from healing back together as it dries.  The pizza cutter also is not so sharp that it will slice up your window screening.
    A second long narrow table is used to load the cut tile onto the wire shelving for drying. You pull on the exposed window screening, not the clay, and the whole 4 foot long length of clay slides from table 1 to the top of the shelf sitting on top of table 2. The table tops need to be the same height to do this without flexing your wet clay.
    A roller conveyor could be used for supporting simple pugs of clay, but it will not do the job for tile processing.
    You could use your wooden boards or drywall as the support surface under table #2. However, I use the window screen and the wire shelf to create a pathway for air drying on the underside of the tile. My shop makes hundreds of square feet of tile for many orders and this is the only production efficient method I have found so far. 
    By the way, the wire shelves are stacked on bakers racks, sourced from a restaurant supply store. These are much less expensive than ceramic ware carts.  If you use boards or drywall, you will just need to see if the bakers rack dimensions can work for you, or if you need to buy the trays for the rack that would work as shelves. 
    Hope this helps, and let us all know if you find any other tile making efficiencies. 
  5. Like
    PeterH reacted to neilestrick in Glaze Fire Closed Forms   
    The pot will not explode without a hole in it. Only moisture causes explosions, and that's hard to do in a glaze firing unless you just glazed it and put it into a kiln that's firing really fast, like Raku.
    The pinhole is not even necessary in a bisque firing. Closed forms can be fired just fine without any holes. You just have to let them dry for a really long time, or give them a long preheat in the kiln, because they take forever to dry. The outside can be bone dry, with the inside still leather hard. The trapped air will not cause an explosion, though. In a firing, the trapped air only expands about 1.6X- not enough to blow apart a pot. When water turns to steam, it expands 1,700X, and that will blow up a pot.
  6. Like
    PeterH reacted to JohnnyK in Glaze Fire Closed Forms   
    The way I see it, Shelly, one of three things may happen. 1: nothing, the piece will be fine. 2: the glaze will melt and the expanding air in the piece will blow it out of the hole, venting the piece. 3: the piece will explode. If the piece is that important to you , I would guess as to the place you think the hole might be and clean the glaze off to reveal the hole, put a toothpick or whatever fits in  the hole, reglaze, unplug the hole and fire. How are you supporting the piece to keep the glaze off the kiln shelf when you fire it?
  7. Like
    PeterH got a reaction from Min in Bone China casting issue   
    Hamer&Hamer mirror Min's concerns on wreathing and deflocculation.  https://tinyurl.com/yyx5z39l
    However they add that "swirling the remaining slip around the mould before draining may help to overcome the problem".
    PS for what it's worth
    Valentine's recommend an identical slip recipe for use with their Fine Bone China Granulate.
    https://www.valentineclays.co.uk/product/fine-bone-china-granulate
    When making casting slip from their plastic clays they recommend using both sodium silicate and soda ash for all except the bone chinas.
    Irritatingly they also give suggested control parameters for all but the bone china.
    https://www.valentineclays.co.uk/sites/default/files/downloads/Technical Analysis Chart - Industrial Products.pdf
     
  8. Like
    PeterH reacted to Min in Bone China casting issue   
    From Frank Hamer: "Wreathing or livering, which is a rippled or uneven surface on the inside of the cast, and roping, which is when this uneveness is in raised lines: The slip has insufficient thixotropy . The sodium silicate should be reduced and if necessary the sodium carbonate increased to maintain a working fluidity. Swilling the remaining slip around the mould before draining may help to overcome the trouble." Quote from this. 
    From Walker Ceramics, description of wreathing: "small uneven ridges on the slip side of the article" and cause for wreathing is "slip thixotropy to low", fix "decrease Dispex addition" 
    I emailed Valentine's and asked why there is no soda ash in their porcelain and china clay casting slip recipes and got this reply: "Generally speaking there is no Soda Ash used when making slips that don’t contain Ball Clays, Ball clays react better using a combination of Soda Ash and Sodium Silicate and these are both described as deflocculants"  
     edit: couldn't open your link to the Frank Hamer tiny url link @PeterH , found it elsewhere and quoted it in case there are issues with my link also
  9. Like
    PeterH reacted to Min in Bone China casting issue   
    They did't call for adding soda ash as well as sodium silicate? Just using the latter can make a "stringy" slip, I'm wondering if that's causing what you're experiencing.
  10. Like
    PeterH reacted to Fred Sweet in Scandia Ovnen IWG350 gas kiln info   
    mr.cyclopede-
    You May want to do a little research on changing orifice sizes at Ward Burner Systems. Mark Ward has a copies of articles he has written on his website. Of particular interest to you might be the following: http://www.wardburner.com/orificesmessing.html
    He also has an orifice chart and replacement orifices available at: http://www.wardburner.com/otherproducts/orificechartsplugs.html
    If you would like to contact him directly to find out whether he can confirm the suitability for Scandinavia kilns, use the following: info@wardburner.com
    Hope this may be helpful to you.
    Regards,
    Fred
  11. Like
    PeterH got a reaction from Rae Reich in Does a glow in the dark lustre exist?   
    Don't know about lustres, but there was a flurry of interest in "glow in the dark" glazes some years
    ago.  I even saw small quantities of the phosphors for sale, with low-fire glaze recipes. Sadly a quick
    look didn't find anything currently available on the retail market. Probably a fair amount available
    wholesale from China!
    Like most "luminous" substances they probably require some exposure to sunlight/UV to "charge" them.
    A few urls to give you the idea:
    https://ceramicartsnetwork.org/wp-content/uploads/2009/02/cmjja04glowingglaze.pdf
    http://www.potters.org/subject94692.htm
    http://www.gtamart.com/mart/products/phspgmnt/glaze.html
    http://www.luminggroup.com/english/product/index.asp?sid=165&sel_id=151&sel_id_02=165
     
    There seem to be other pigments (perhaps glazes) that simply glow under UV light.
    https://www.darkniteglow.com/product/uv-light-reactive-powder/

    Regards, Peter
    PS A search with a more scientific terminology "photoluminescent glasses" found
    https://tinyurl.com/y2aw55bo
    The ones based on strontium aluminate may well work in a  low-fire glaze which doesn't dissolve it.
    ... wiki gives "temperatures above 1090 °C is likely to cause loss of its phosphorescent properties"
    Vaguely relevant paper https://pdfs.semanticscholar.org/6ecd/665a0fcfe721fd4431e40583faac200e80fc.pdf
    ... which unfortunately doesn't seem to say what glaze they used, nor why they mixed it with alcohol rather than water.
  12. Like
    PeterH got a reaction from Magnolia Mud Research in Does a glow in the dark lustre exist?   
    You are absolutely right, I very much doubt that doped crystals could reconstitute themselves, even if the firing conditions were ideal for
    recrystallization of the host crystal itself.
    Regards, Peter
    The "why they mixed it with alcohol rather than water" point I'm less clear on. I mentioned it in case anybody else could spot it's significance
    (if any). As you bring the point up I'll elaborate on my position.
    I didn't believe that strontium aluminate was water soluble, but I couldn't find a handy reference giving an actual number. I did find several
    data-sheets claiming that it was insoluble in water -- but also one that suggested that is was soluble in water. However use of water-based
    media such as acrylic seems to be recommended for the pigments. So my current belief is that water solubility just isn't an issue.
    I suspect that the chemists used alcohol-based techniques in the preparation of the glaze because (in their line of work):
    - It's what they are used to doing (accuracy and reproducibility are important to them, so tried-and-tested is rightly valued)
    - You can evaporate alcohol easily, especially with a mild vacuum (time is money)
    - The cost, H&S and waste-disposal issues are insignificant in a lab context
    But that's probably because it's the only vaguely plausible explanation I can come up with.
  13. Like
    PeterH reacted to Babs in Using Tile Extruder Machine (Peter Pugger)   
    He she will be notified by email of your message which can be read as an email, not necessary for that person to log into this forum to read it if that makes sense.
    This will work if email address is still current.
  14. Like
    PeterH reacted to Yomama in Using Tile Extruder Machine (Peter Pugger)   
    Just sent it. I hope it gets to her. 
  15. Like
    PeterH reacted to liambesaw in Does a glow in the dark lustre exist?   
    Nope, they might have a glow in the dark enamel though
  16. Like
    PeterH got a reaction from Magnolia Mud Research in Does a glow in the dark lustre exist?   
    Don't know about lustres, but there was a flurry of interest in "glow in the dark" glazes some years
    ago.  I even saw small quantities of the phosphors for sale, with low-fire glaze recipes. Sadly a quick
    look didn't find anything currently available on the retail market. Probably a fair amount available
    wholesale from China!
    Like most "luminous" substances they probably require some exposure to sunlight/UV to "charge" them.
    A few urls to give you the idea:
    https://ceramicartsnetwork.org/wp-content/uploads/2009/02/cmjja04glowingglaze.pdf
    http://www.potters.org/subject94692.htm
    http://www.gtamart.com/mart/products/phspgmnt/glaze.html
    http://www.luminggroup.com/english/product/index.asp?sid=165&sel_id=151&sel_id_02=165
     
    There seem to be other pigments (perhaps glazes) that simply glow under UV light.
    https://www.darkniteglow.com/product/uv-light-reactive-powder/

    Regards, Peter
    PS A search with a more scientific terminology "photoluminescent glasses" found
    https://tinyurl.com/y2aw55bo
    The ones based on strontium aluminate may well work in a  low-fire glaze which doesn't dissolve it.
    ... wiki gives "temperatures above 1090 °C is likely to cause loss of its phosphorescent properties"
    Vaguely relevant paper https://pdfs.semanticscholar.org/6ecd/665a0fcfe721fd4431e40583faac200e80fc.pdf
    ... which unfortunately doesn't seem to say what glaze they used, nor why they mixed it with alcohol rather than water.
  17. Like
    PeterH reacted to Hulk in Making slip from clay trimmings   
    Hi cstovin!
    I don't slipcast - that said - I do watch vids!
    Are you using plaster molds? ...plaster absorbs moisture, which should firm up the slip closest to the mold.
    Are you pouring out/back the slip some time after filling the mold? I'm seeing that molders are casting "hollow" pieces. The slip up against the mold, being stiff enough to resist flowing, stays in the mold; after pouring, the remainder has air on one side, plaster on the other - now wait for the casting to dry some more before splitting the mold! ...experience tells how long to wait before pouring, and how long to wait before splitting. Looks like thickness is about 5mm or so - not so thick as to split/crack, and not so thin as to break easily either. 
    A quarter sized puddle of slip dries to leather hard on my plaster bat rather quickly, hmm... 
  18. Like
    PeterH reacted to Babs in Pugmill for tile extruding   
    Great book
    Handmade tiles by Frank Giorgini
    ISBN 1-86351 -164-4
    Sally Milne publishing.
    Your local library may have it or get it in for you.
    Very comprehensive.
     
  19. Like
    PeterH got a reaction from Min in 2 piece bowl mold help!!!   
    No, a space between the walls is not normal. Indeed if you use the normal "drain casting" methods there is no way for this to happen.

    What you seem to have is a mould that relies on "solid casting", in which both the inner and outer layer of your bowl are cast against plaster, as in this plate mould.

    If you just fill a mould like the bottom one with slip you are in trouble. The original slip shrinks as the mould draws water out of it, leaving air holes.
    So you must keep topping up the mould with slip until the solid-cast portions are completely full of drying clay. (Sometimes the mould is designed
    to hold all the extra slip required, in which case you don't need to top-up.)
    Solid casting a a bit trickier than drain casting: it's more demanding of the quality of slip, and usually has concave sections that you need to de-mould
    as quickly as possible (and no sooner!) to avoid them sticking in the mould. This web page describes the process:
    http://butterflyceramic.blogspot.com/2013/01/a.html
    Regards, Peter
    PS Here is a video of somebody filling a solid cast plate mould. Note the fluidity of the slip, and the ease with which it passes through the caster's sieve.
    Of course you cannot just dilute your slip to that consistency with water, it has to have both the right clay:water ration and state of deflocculation.
    -------------------------------
    Sorry, cannot get rid of this dratted image/attachment, please ignore.

  20. Like
    PeterH reacted to Callie Beller Diesel in Making Decals using HP Laser Jet Printers with toner made by Laser Cartridge Pllus   
    The paper is a whole other story from the toner. 
    Are you wanting to use a tissue transfer method or to make waterslide decals?
    If you wish to use the tissue transfer method that works better on a bisque surface, a roll of rice paper from amazon cut to fit your printer and a bottle of orange cleaner or wintergreen oil can be had for under $40. 
    Waterslide decal paper is currently a complicated issue if you live in the US. The drama is covered here. 
    If you live outside the US, as a Canadian I can send you information via DM on waterslide decal paper sources, but I can’t post it openly for reasons in this other thread. 
  21. Like
    PeterH got a reaction from Min in Need help identifying glaze materials   
    [I may be reading your ref too quickly, but is seems to say metallic barium melts at ~ 1300F. However as wiki gives the MP of BaCO3 as 811C (1,492F) your point remains a good one.]
    Many years ago I was astounded to read that quite a lot of the barium sulphate in a Jasper body survived the firing. I'd
    assumed that it would simply decompose. Trying to find a reference I looked in "Ceramic Masterpieces" and found this:
    During firing at a temperature of about 1250C, a portion of the barium sulfate reacts with the clay components to form a
    barium-aluminium-silicate matrix containing residual barium sulphate particles. The matrix is a mixture of a glass with fine
    particles of barium-aluminium-silicate (celsian) and barium silicate (sanbornite) ...
    From which I assume that the barium sulphate in the body either remains unchanged† or enters into the molten glassy matrix
    liberating SO3 (later the barium micro-crystalises out on cooling). It would make sense if the barium carbonate in a glaze did
    much the  same. So in high-alkali raku turquoises the BaCO3 would be completely decomposed, while in a full-blown barium
    matt perhaps some unchanged BaCO3 remains.  Just a guess.
    Regards, Peter
    † Wiki gives the MP of BaSO4 as 1,580C (2,880F) and https://chemiday.com/en/reaction/3-1-0-3287 gives the decomposition temperature as "over 1580C".
  22. Like
    PeterH reacted to Bill Kielb in Explanation for Error Code 1 on Skutt 1027 Kiln?   
    @ango0211  @Kyle
    SAVING THE WORK
    I believe this is a three zone kiln, so when this happens it often is one or more failed relays. In our kilns I try and diagnose this quickly and not unload the thing.
    CAUTION LIVE ELECTRIC:
    In our studio we shut the kiln down, back probe all the elements and make sure they are good. Assuming they are good, we run the control in test mode to find the offending relay, replace it, and restart the firing. For the most part the wares come out fine as most of the heatwork is done in the last 250 degrees of the firing.
    CAUTION LIVE ELECTRIC:
    If you are not familiar with the diagnostic routine of  your kiln control you can program a single segment, go as fast as you can type program to some temperature above the current kiln temp. All relays will engage and you can find the bad one easily with a clamp on ammeter. It is also possible you have a bad element, worn elements or burned wire but these are progressively less likely than the relay.
    Bad element. - hopefully  you would have noticed the break while vacuuming but checking by back probing allows this to be checked first. If so, ya gotta unload and fix.
    Worn  elements - your firing times will get longer so your slow bisque firings would grow to 16 or more hours. Your glaze firings would grow to ten or more hours. You likely would have noticed. Almost all kilns today need all elements to work reasonably well to make it to cone six.
    Burned wire - Not as likely as one of the relay crimp connectors being burned visibly actually. This is quite visible when you open it.
    Bad thermocouple - not likely cycle through T1,T2,T3 in your control to confirm each read a temperature.
    so if you do this yourself, ELECRiCAL SAFETY first and foremost because the relay test requires a live machine be tested. Your kiln tech should easily be able to do this as well, it literally takes minutes.
    Finishing the firing without unloading  and reloading saves us a whole bunch of time and effort. This is not a decent kiln tuneup or maintenance plan though, it is designed to just get you through this firing.
    Don't forget to double check your firing program before restarting
    Simple replacement video:
     
  23. Like
    PeterH reacted to Dick White in What is Lith-O-Sil please?   
    The following is a mixture of facts, speculation, and invention off the top of my head. Some months ago there was a hew and cry in several pottery-related Facebook groups about an impending demise of the availability of spodumene. Everybody was rushing to buy the last available material from their usual sources and there was much rending of clothes that they would not be able to make their favorite glazes anymore. I never saw any rigorous business analysis of the issue (other than the obvious market impact on the price of lithium caused by the huge demand of the lithium ion battery industry) to explain a cessation of availability of spod. Some US-based commenters pointed to their favorite suppliers having warehouses full of the stuff. The only logical comment I saw in all the discussion was from an EU-based person who indicated there was some EU regulation that forbade dividing branded merchandise into smaller quantities and reselling it in unauthorized packaging. The company mining spodumene in western Australia (generally referred to as Gwalia Spodumene) supposedly ships its product to distributors worldwide only in very large ~200 pound sacks, and distributors would rebag it as needed for local resale. It was this end-of-supply-line issue that ran afoul of the EU regulations. There hasn't been much noise recently about "what should we do now that spod is gone" as there was at the turn of the century was when the gerstley borate mine closed, so perhaps it was much ado about nothing, a false alarm. Or perhaps the ingenuity of the potters in affected areas developed a workaround - source the spod (and lithium carb) in the standard big bags from the original producer and reblend it with an immaterial amount of something innocuous into your own proprietary product and sell it in whatever quantities you wish in your own bag?
  24. Like
    PeterH reacted to Min in Low Expansion Cone 10 Clear Glazes   
    @LeeS,I’m just going to pile on a bunch of info that I think is pertinent to your questions.
    Simplified Periodic Table, I’m including this to show why I suggested lithia (using spodume) and why magnesium would also be a good flux to look at.

    In order to have the least effect on changing the qualities of a glaze when it is necessary to do so on the flux level (rather than with silica and alumina alone) replacing all or part of one flux with another from the same group of elements gives a better chance of success. 
    I’m going to use your G1947U glaze as an example of how I look at altering a recipe. I took out some of the custer to start with. The main reason I did this was to reduce the high expansion oxide potassium (bit of sodium in there too). Okay, fine, so I took some of that out but then in order for the glaze to melt I needed to replace it with something. Only other option in the same group of elements, alkali metals, is lithium. I like to to supply lithium by using spodumene. Obviously the spodumene contains more than just lithium, it contains silica and alumina also, but the beauty of glaze calc is it’s very simple to balance out these. Now, when I removed some of the custer in addition to removing some potassium and sodium it reduced the total calcium also but again, if necessary it’s easy to add some back in using calcium carbonate. 
    Another way to attack this glaze would be to look at what other high expansion fluxes could be reduced. So, a list of materials from high to low expansion below (I’ve included barium and lead just for completeness but don’t recommend using those): 
    HIGHEST Sodium oxide, Potassium oxide, Calcium oxide Strontium oxide, Barium oxide, Titanium oxide Lead oxide, Zinc oxide, Magnesium oxide, Zirconium oxide, Alumina, Silica, Boron LOWEST
    Zinc is already in the glaze, one thing to note with it is if you use a glaze that has either zinc and/or lithia then the amount of boron needed will be less due to eutectics. Could add more zinc but keep an eye on the suggested limits (0.36) can have pin holes and other issues with it.
    Magnesium is next, I think it’s a very good choice. You can supply it with a frit, dolomite, talc or magnesium carb (though that last material can bring in unwanted issues). So, if you go back to that mini periodic table above you see that magnesium is in group 2, the alkaline earths group. Many glazes contain calcium (also an alkaline earth) but look how much higher up the list of expansion materials it is. If I was going to use some magnesium to lower the COE of a glaze I would take out some of the calcium and rework the recipe to get some magnesium in there, probably using dolomite or talc or a frit. This way you aren't messing up the R2O:RO flux ratios too much.
    Boron is next, it used to be thought of as a flux as it gets low and midrange glazes to melt so well but it's a glass former. It isn’t necessary at cone 10 but it can be used. 
    One other thing that is sometimes used is zirconium. I know you are looking for a clear glaze but the addition of just 2 or 3% shouldn’t effect the clearness of the glaze and it does help reduce crazing.
    I would suggest printing off a copy of the suggested limits for cone 10 (they’re not written in stone but somewhere to start for guidance) then spend some time using Insight and which ever recipe(s) you had the least crazing with and go from there. The CMW MAG Gloss from Matt Katz might work, but it might not be clear enough due to the high talc level. That would be one I would also try, as is but also with some boron and with some spodumene in place of some of the talc. I would run 2 recipes, one with some gerstley borate, one with some spodumene. (you said you didn’t mind a lot of tests ; )
    One last thing, COE figures are not absolute, they work best when comparing glazes that use the same ingredients. By adding spodumene to the G1947U glaze I’ve changed the “system” of that glaze so it might be okay with a higher or lower COE than the same glaze without the spodumene. If possible try to change just add one variable (flux) in a glaze at a time. Once you get a glaze that fits then by comparing the COE's of other glazes it will get you in the ballpark of what will fit but it won't be absolute.
    Hope I haven’t thoroughly confused you. Play around with Insight, come up with what you think might work and post it here so we can give some thoughts.
    edit: re 1:1 substitution of one flux element for another, nope can't do it like this as some have much stronger or weaker fluxing power at certain temps than others.
  25. Like
    PeterH got a reaction from Babs in How to season giant clay pots without glaze or kiln   
    Background
    Some reasons why you might  want to use clay vessels in winemaking today are given in
    https://www.winemag.com/2018/05/30/aging-wine-in-clay/
    Clay is the happy medium between the two. Like oak, clay is porous, allowing for an exchange of oxygen.
    Like steel, clay is a neutral material, so it doesn’t impart additional flavors.
    I think that Roman wants to get a porosity "similar to that used in terracotta winemaking vessels".
    Or at least  an indication of just how dry/damp/soggy an earthenware body fired to bisc would be
    when filled with liquid. 
    I seem to remember that the forum has reported earthen pots leaking/seeping sufficiently to
    damage the surface they are standing on (after the waterproofing glaze has crazed).  
    (Aptly enough it's in the thread vases leaking water!)
    Regards, Peter
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