oldlady Posted October 7, 2020 Report Share Posted October 7, 2020 really dumb question here. it sounds as though you have an electronic controller on your kiln. i have always used the built in slow bisque and slow glaze back when i did bisque before glazing. have you tried your controllers basic slow bisque and slow glaze firings without adding any kind of hold or anything else? (it would be helpful to the group if you put a location in your avatar. you might find that you live next door to one of our members.) Link to comment Share on other sites More sharing options...
Hulk Posted October 7, 2020 Report Share Posted October 7, 2020 Hi Nat, The "problem" clays include light red, cafe, very red, and black. Two bisque loads back, I extended the holds to ~20 mins at 750, ~30 mins at 1050, and almost an hour at 1500F; the subsequent glaze fire had no bloats in the black clay pieces... My kiln is fully manual, so it's check, set switches, repeat... That's where the notebook comes in handy, heh. I stuck with the same schedule for the most recent bisque, although almost all the work was "Venus White" and bmix - there were a few cafe (light brown) and light red pieces in there. I'd changed up three things - bisque schedule, peak glaze temperature, glaze drop and hold - didn't want to change anything "back" just yet! Are you getting lots o' oxygen in both bisque and glaze fires? Link to comment Share on other sites More sharing options...
Nat P Posted October 7, 2020 Report Share Posted October 7, 2020 Hi Hulk .. I assume that with the vent hole at the bottom of the kiln I am getting as much oxygen as possible . The clay body is a medium white stoneware . Link to comment Share on other sites More sharing options...
Nat P Posted October 7, 2020 Report Share Posted October 7, 2020 Hi Oldlady .. golly if you are in your 20's I'm ruined. LOL Thank you for your question . Yes, the presets had been working well until now. Link to comment Share on other sites More sharing options...
Min Posted October 7, 2020 Report Share Posted October 7, 2020 2 hours ago, Nat P said: Attached are a few new glazes that we were going to try . If there are any that stand out as good or bad please let us know. Hmmm, there are some things that stand out. First glaze is going to be a high expansion glaze, might be fine on your claybody but it would craze on many claybodies. Alumina is a titch high, reason this makes a difference is it will contribute to a stiffer glaze melt. Second glaze there is no way I would even bother testing, way too much gerstley borate. You will have a bucket of gelled glaze with too much boron. Third glaze has far too much silica and alumina. What type glaze are you looking for and do you measure the specific gravity of your glazes? Link to comment Share on other sites More sharing options...
Nat P Posted October 8, 2020 Report Share Posted October 8, 2020 Hello , Thank you for looking at these . Great to know which ones to steer away from right off the bat ! We are looking for a white gloss glaze with a slightly warm tone , not too harshly " liner glaze " Cone 6 . It needs to have consistent coverage as we applying with brushes. That's it . We do not measure the specific gravity other than the good ole finger test. : ) Link to comment Share on other sites More sharing options...
Bill Kielb Posted October 8, 2020 Report Share Posted October 8, 2020 1 hour ago, Nat P said: We are looking for a white gloss glaze with a slightly warm tone , not too harshly " liner glaze " Cone 6 . It needs to have consistent coverage as we applying with brushes. That's it . We do not measure the specific gravity other than the good ole finger test. : ) Funny thing about glazes is you really need to test them with your clay, your application and your firing. Most recipes you likely find posted will not be formulated for brushing so maybe trying several commercial glazes is the route you should go. My other thought is to search a site like Glazy.org and pick cone six gloss glazes to try. While not for sure, if the flux ratio, (R2O:RO) is in the range of 0.2:0.8 - 0.3:0.7 it is a reasonable indicator that the glaze may be durable as a liner. While not a final say, we know as glazes stray from this ratio, they are more likely to be less durable as a liner. I will add a gloss glaze should likely have a silica to alumina ratio range of (Si: Al) 6.5:1 - 10:1 as well. Things that fire to a significant different gloss level than their compositions indicate are often under fired / overfired and quite possibly not durable. Again without testing durability there is no way to know for sure but the above guidance can help rule out likely less durable glazes. Glazy.org example below, but in the end you will need to test to ensure it fits and is what you like. Testing SPG establishes a uniform baseline for yourself and your use. If your dripping finger works consistently all the time then that’s your method. Link to comment Share on other sites More sharing options...
Min Posted October 8, 2020 Report Share Posted October 8, 2020 5 hours ago, Nat P said: We are looking for a white gloss glaze with a slightly warm tone , not too harshly " liner glaze " Cone 6 . It needs to have consistent coverage as we applying with brushes. For brushing glazes are you using a brushing medium to mix with the water when you mix up the test glazes or a CMC solution as part of the liquid? Most economical way of turning a dipping recipe into a brushing one is to substitute about 1/4 to 1/3 of the water needed to CMC solution. Each glaze is going to be slightly different in the amount of CMC solution required to give the glaze the brushability you need but this will get you in the ballpark. If you were using a dipping glaze recipe and mixing it up to resemble a brushinging glaze in thickness that would probably have been the cause of the pinholes. (Specific gravity will be too high, ie too high a dry materials to water ratio). If you need it the recipe for making CMC solution is 35 grams of CMC powder sprinkled onto 1 litre of very hot water and then leave it to sit overnight. In the morning whizz it up with a hand held immersion (stick) blender. If there is no copper in the glaze then add 1/4 teaspoon of copper carb to stop the CMC from rotting. This tiny bit of copper won't noticeably effect the glaze colour. I do think you need to measure the specific gravity (SG) until you get the glaze working how you need it to. After you have used it a few times then you get a feel for how it should look when you stir it up (or dip your finger in it). To take away some of the harshness of white glazes adding 1% or so of rutile or iron oxide can help. Rutile will tend to give more of a tan/yellowish hue than iron. edit: curious why you choose to brush your glazes? Link to comment Share on other sites More sharing options...
Hulk Posted October 8, 2020 Report Share Posted October 8, 2020 measuring, adjusting, and keeping notes on specific gravity - each glaze, for some work better higher/lower - along with tweaking for thixotropy has made, err, is making all the difference in dipping, for me; eliminating runs and drips, consistent/repeatable thickness, faster as well. Should read less runs and drips, and more consistent thickness, still working on it - I have better luck waiting for the moment the glaze begins to change tone, whilst the drip is still liquid but starting to set up near the edge of it, to smooth with a dampened finger, over working with it dried. For thickness, given same clay, surface, thickness, dryness, and same stirred glaze, looks like timing and technique... Oh, Nat, on the venting, wanted to suggest verifying that it's working ok - does it pull hard enough to draw smoke at the lid hole? If not, is the exhaust warm, also, during wax burn off it will smell quite a bit, even downwind a ways. Among the hypothetical problems, a tight kiln room - where there isn't a path for air to return to "make up" what the kiln fan is blowing out. Since bisque was a topic, just asking, and O2 might matter in the glazing as well, perhaps when using a high loi glaze? Link to comment Share on other sites More sharing options...
oldlady Posted October 8, 2020 Report Share Posted October 8, 2020 nat, in response to your request for a white glaze recipe, here is one from a book published by George Wettlaufer in 1976. a chemical engineer whose glazes are made to work with lots of different clay bodies. if you can find a copy of the book, you might really like it though you will cry at the cost of everything mentioned that a starting potter would need. i thought i have some samples of the glossy white glaze in my albums but there is only one. over the years, some materials may have changed but i bought a lot of full bags many years ago and still have lots of most of everything. if you leave out the zircopax, it will be clear. glossy white cone 6 soda spar (C6) was suggested 40 whiting 20 ball clay ( C&C is very white) 10 zinc oxide 5 silica (325) 20 zircopax 20 i do not brush at all so this may not be right for brushing. it was intended to be poured or dipped. i spray greenware. why do you not pour the interiors, it is easier. Link to comment Share on other sites More sharing options...
Nat P Posted October 9, 2020 Report Share Posted October 9, 2020 9 hours ago, Bill Kielb said: Funny thing about glazes is you really need to test them with your clay, your application and your firing. Most recipes you likely find posted will not be formulated for brushing so maybe trying several commercial glazes is the route you should go. My other thought is to search a site like Glazy.org and pick cone six gloss glazes to try. While not for sure, if the flux ratio, (R2O:RO) is in the range of 0.2:0.8 - 0.3:0.7 it is a reasonable indicator that the glaze may be durable as a liner. While not a final say, we know as glazes stray from this ratio, they are more likely to be less durable as a liner. I will add a gloss glaze should likely have a silica to alumina ratio range of (Si: Al) 6.5:1 - 10:1 as well. Things that fire to a significant different gloss level than their compositions indicate are often under fired / overfired and quite possibly not durable. Again without testing durability there is no way to know for sure but the above guidance can help rule out likely less durable glazes. Glazy.org example below, but in the end you will need to test to ensure it fits and is what you like. Testing SPG establishes a uniform baseline for yourself and your use. If your dripping finger works consistently all the time then that’s your method. Link to comment Share on other sites More sharing options...
Nat P Posted October 9, 2020 Report Share Posted October 9, 2020 WOW ! Thank you Community ! So many great ideas to explore . We are newly energized to find a solution. Bill : Thank you for the glaze recipe and all of the notes . We have made up 5 different test batches of glaze ( including the Studio white ) and have 5 new claybodies to try. This is our " we are starting over " plan of action ! Oldlady : Thank you also for the recipe! We brush in order to get consistent coverage. We have poured but with the white on white the pour marks can become problematic. We intend to move to spraying once we get that set up but while trying to solve the pinhole issue we have put that aside. Love that you do a once fire spraying greenware ! Hulk : We are going to research about how to measure specific gravity. Dripping has never been an issue with our glaze. It for a very long time has been great. Since I did just install the vent I will double check to see the pull through the kilns. Good Idea ! Honestly though, the kiln was not vented before and everything in the once upon a time land so far off from this debacle was working just swell. Min : awesome . Thank you for the advice on how to change a glaze formula for brushing . I will look into the CMC Solution . Notes : We are trying our original glaze formula with distilled water and adding 2% bentonite in the mix of new glazes. ** One thing , I had not mentioned before is does anyone know why a glaze would smell a little like sulfur ? I definitely had also noticed quite a bit of what I assumed was iron in water creating a darkness in the water on the top of the glaze before stirring to use. Thank you . Link to comment Share on other sites More sharing options...
Hulk Posted October 9, 2020 Report Share Posted October 9, 2020 Hoping for good results! Please do post back how it goes. Measuring the wetness of glaze - specific gravity - allows for repeatability; else, it's a variable! Too wet/thin, takes longer to get thickness, then longer for the ware to dry, and more difficult to control drips. Too thick/dry, more difficult to get the desired thickness of glaze (guessing, haven't pressed that end of the spectrum)? More wet/thin, the time window for hitting the desired thickness is bigger, and, given the glaze gels well - has sufficient thixotropy - it levels well and doesn't drip. Yesterday, got through liner glazing most o' the next glaze load. ...won't say I'm getting good at this, noooo, however, can say there's progress! I pour in a ladle full (mix each time! mix't good!), pour it out such that the last bit of pour is just at the part of the rim where the pour started, give it a vertical shake, then a twist shake or two, wait just a bit, then touch the rim to pick up a bit more glaze there and get the liner past the rim about 3mm or so, twist shake, wait a bit for the glaze to gel, done. Sometimes there's a thick spot to smooth with a wet finger. It's getting easier, faster, and better - looking forward to more practice. If the glaze moves at all in firing, the rim will be thin, so have been picking up a bit more at the rim - seems to be working. Other variables, hmm: how long the ladleful sits before pouring out begins; how fast the pouring out is done - how long the glaze puddle is in contact with the wall; how even the pouring out is done; if shakes are completed whilst the glaze can still move (leveling the glaze layer); if any drips (that didn't shake off) are run around enough to make'm disappear; if any drips, then smoothed in at just the right time. Still working on it; will post a pic of liner glaze later today, just for fun! I'm using a cheap plastic 100 ml graduated cylinder and my (also somewhat cheap!) digital scale to measure SG; fill to the 100 ml line, weigh, subtract the weight o' th' cylinder (43.8 g - or just zero on the dry mt cylinder), voila, write it down! From there, I look to adjust thixotropy just before glazing - right after sieving; I'm stirring clockwise, in time with Rastaman Vibrations, then watch how it slows, and also the "bounce back" when the slurry stops. At the less thixotropic extreme, the slurry just keeps on spinning, and the shear between the faster and slower currents is apparent; the the other extreme, the slurry takes less than three turns, stops all together, and bounces back, a lot. I'm shooting for about three to three and a half turns, and perceptible bounce back. Any road, I'm guessing the pinhole problem is due to the clay. Whilst it would be most interesting to make only one change at a time, and hence isolate/pinpoint the problem(s), getting past the problem asap is likely better. Bisque it good. Did some glaze spraying at the local JC ceramic lab (took a year of classes there). I like spraying, however, may not ever get around to setting up for it in my home studio. For one, I'm cheap! Spraying means overspray, and although I'm certainly Not above collecting and using "waste" glaze (I'm that cheap), I'd rather not be making it at a higher rate. Spraying involves technique and skill. I'd like to think I get to make that statement, having run airless and conventional rigs for thousands of hours. Is spraying easier to master than dipping/pouring? idk. Just to start, keeping the glaze mixed, and setting the ideal SG and thixotropy are challenges, then setting up the gun/pressure, learning to trigger, how to get an even layer, etc. Stencils are so easy with spraying! https://digitalfire.com/glossary/pinholing https://digitalfire.com/glossary/thixotropy https://digitalfire.com/trouble/uneven+glaze+coverage see also Tony Hansen's video on adjusting sg and thixotropy Link to comment Share on other sites More sharing options...
dhPotter Posted October 9, 2020 Report Share Posted October 9, 2020 @HulkSpraying - You can do it !! Granted it took me 5 loads to figure out how thick to spray - that was before I saw OldLady's suggestion of spraying till the glaze looks like "Chunky Velvet" - works nearly every time. The SG on these sprayed glazes, for me, is around 150-155. Set your compressor for about 42 psi and when you pull the trigger the psi will be at 40 - perfect for my Critter spray gun. As far as keep mixing the glaze - fire you some 1 inch clay balls to maturity to make ball bearings - place 2-3 in the sprayer jar. As you spray, periodically swirl the ball bearings around to pick up what has settled to the bottom of the jar. Even layer - spray till the spot looks wet then move on - really get into a good rhythm spraying and spinning the banding wheel. Spray over the piece multiple times to even the glaze out. Over Spray - You do not have to pull the trigger all the way. Also, direct the spray more at the target inside off to the side of the piece. For a very cheap spray booth - make it out of a big plastic garbage can and a PC fan - I used this for a year till I decided spraying was for me. The design was on a lady's facebook page but I cannot find it now. However, I saved all the pics and instructions in a Word Doc. Link to comment Share on other sites More sharing options...
Min Posted October 9, 2020 Report Share Posted October 9, 2020 5 hours ago, Nat P said: I had not mentioned before is does anyone know why a glaze would smell a little like sulfur ? I definitely had also noticed quite a bit of what I assumed was iron in water creating a darkness in the water on the top of the glaze before stirring to use. Discoloured water in a glaze bucket is from solubles coming out of materials, stir it all up, it will be fine. Can't say I've ever had a glaze smell like sulphur, perhaps your water supply? Does your water smell eggy? Link to comment Share on other sites More sharing options...
C.Banks Posted October 9, 2020 Report Share Posted October 9, 2020 8 hours ago, Nat P said: One thing , I had not mentioned before is does anyone know why a glaze would smell a little like sulfur ? I definitely had also noticed quite a bit of what I assumed was iron in water creating a darkness in the water on the top of the glaze before stirring to use. Thank you . I have a bucket of glaze that used to smell like sulfur I added some drops of tea tree oil and it's better this year. The smell was pretty the same as an old bucket of clay. I've used a bit of bleach in my reclaim if it starts to get a bit swampy. Tea tree smells better. Link to comment Share on other sites More sharing options...
Hulk Posted October 10, 2020 Report Share Posted October 10, 2020 "... 1 inch clay balls..." - great idea dh! To check spray thickness, I placed a small tape squares (turned an eighth, hence a diamond), which, when pulled off, reveals the thickness. I still poured the liners, then balloon masked the interiors for spraying the exterior, having waxed and cut a sharp line*. Brushing (imo) also involves skill and technique; I be dippin' an' pourin' for now... Here's some liner pours. From there, some will get dipped foot first, overlapping the outside glaze with the liner, just a bit; others will get waxed, cut*, and dipped the other way for a sharp line at the rim. Fairly smooth and even - there's a few ridges, pour lines, etc., here and there - I'm going with it. * It's a bit of trouble, but does produce a clean edge: https://digitalfire.com/article/how+to+liner-glaze+a+mug Link to comment Share on other sites More sharing options...
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