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David Woodin

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Posts posted by David Woodin

  1. So far I have not had any issues with my wares coming out of the kiln that could not be attributed to firing profiles which corrected pin-holing and such.  Being new I was simply doing the glaze S.G. thing because I had read it was important and thought perhaps I am missing something. 


    To date I have kept by glazes in buckets with Gamma seals (O-ringed), so any significant evaporation is not occurring due to leaky lids. 


    I have a question.  Does the very act of dipping bisque change the water/solids ratio over time or is it more an issue of evaporation due to storage that does this and or both?

    There is another way to find out if your glaze  has the right consistency and that is to use a spatula, stir the glaze and then at about a 30 deg angle let the glaze roll off and count the drips.  So if it runs off like water it is too thin, if it runs off than drips about 6 to 7 drips, at least for me it is fine.  Yes the consistency will change as you are glazing pots.


  2. I use containers 1 quart from home depot for the 4 corners.  The individual cups are used yogurt cups about 6 oz.  The test tile, because I am interested in vertical tests are extruded test tiles long enough to make 5 tests per tile times 7 tiles for the 35 grid.  I only use 300 gram batch  for the corners.  The syringe is 60 cc McKesson Syringe without needle order 102-SC60C20.  Each cup has 48 Milli Litres per sample.


  3. With respect, love and gratitude to everyone who is trying to help, I don't need any more new clear recipes. People have shared most generously in this area. I need help figuring out how to test one that I have already chosen because it meets most of my criteria. I just need to get it so it meets ALL of my criteria.


    Maria, Insight Live includes three different sets of limit formulas to compare cone 6 glazes to. My clay body is red, and seems to contain sufficient silica that crazing isn't a big issue. I want a clear that looks good on red clay. I can accept some yellowing because it won't be obvious over dark clay, but clouding of one kind or another is what I'm trying to solve.


    Joel, I like how the Currie tiles give a lot of information in a small space and use materials economically. Like David suggests, I'll run one on the glaze when I get home from my family reunion next week


    David, thank you again for your materials substitutions.


    I will keep everyone updated when the next batch of tests are done.

    I agree that the Currie method is a great teaching and testing tool.  Unfortunately  if a glaze is not within the cone 6 food safe limits for alumina and silica then the 35 Currie grid also won't have any glazes within the limits but some may look good.  You can customize the Currie grid or can get great results with a custom 20 grid.  This involves keeping the corners within the limits.


  4. Thank you David. It's kind of scary to be doing this for the first time but need to learn it as I've relied on the preprogrammed slow glaze setting for too long. everyone here that programs their own schedules to get the exact result they want have inspired me to try as well.


    A question why would you go to 2018 for ramp 2 instead of 1982? And adding the 5 minute hold here? Is there something that happens to the glaze at this temperature? Just curious and wanting to Learn!


    Getting close! I think it's time to run a test load through and see what I get. I'm going to glaze up a bunch of stuff with the glaze I am having issues with and see if this schedule helps. If not at least I will have something to photograph to show what the issue looks like. So far I have been able to grind the little pimples and bumps down, reglaze and refire with good results. A few that failed in the refire I broke up.



    The top temperature for a 60 ramp rate will now be around 2218 F minus 200 deg = 2018 F.  Orton cone tables are for the last 200 deg F of the firing.  The 5 minute hold is to give the kiln a chance to level out the temperature before starting the final ramp. You can stay with 1982 but all that does is make for a longer total firing firing.  You can play around with the hold if you want.  As for a hold at the end of the firing I usually start  with a 3 minute hold and add to it if necessary.  If you are refiring ware than you may want to go slower on the second ramp, especially if refirng plates, 350F  works for me.


  5. It took me awhile to get back to this but after reading here and the manual some more I think I need to try programming my Bartlett V6-CF using the vary-fire program and the using cone fire option in the last segment. I am going to try to work on the pinholing issue first. I basically used the same schedule as the Slow Glaze Fire EXCEPT that I slowed it down to 80 degrees from the original 120 degrees for the final ramp up to cone 6 in segment 3. This number was mentioned previously, is this a good ramp rate per hour? Too slow too fast? Will doing this give the glaze time to flow and minimize pin holes?


    I would greatly appreciate those of you that are familiar with this controller checking the schedule I have used to see if anything jumps out as bad.


    Below is the info as it flashes back at me when I do the review program option after entering what I think are the correct criteria and setting the schedule to fire under USER 1.


    USER 1

    SEGS 3

    RA 1 150

    F 1 250

    HLd 1 0.01


    RA 2 400

    F 2 1982

    HLd 2. 0.01


    RA 3 80

    CONE 6

    HLd 3 0.01


    DELA 0.00


    ALRM 9999




    FIRE 131


    I am unsure on the HOLD (HLd) for each segment but the manual doesn't show as far as I can tell a hold on each segment under the slow glaze cone fire option, is this correct? Or do I need a hold for each segment? It required a number to be chosen under the Hold so I chose the smallest one of 0.01.


    Also, I think by slowing it to 80 per hour (from 120 per hour) my length of firing will increase by 1 hour? Just wondering if that's how it will work.


    Thanks a bunch everyone!


    You don't need a hold and can enter 0 instead.  I would enter a temperature for ramp 2 of 2018 and a hold of 0.05 minutes. You don't need ERCD on, if it is on and the elements are lagging behind temperature it can shut the kiln off.  Make sure you press review program and ramp 3 says 80 cone 6, before starting the kiln.  Also since this is your first time try to be around for ramp 3 , and make sure it is ramping up at 80 deg by pressing the  review seg button.  After the firing hit review and it will show the final temperature.  If the cones don't show quite enough heat work than you can play with a hold for ramp 3.  You should not need any more than a five minute hold.


  6. David, which unity values are you taking not to be food safe?

    The alumina value is on the border line and the Al/SI ratio of 7.3 isn't going to give a good translucent glaze. According to Michael Bailey "glazes cone 6"  the best clear glazes are around a Al/SI ratio of 9.1 to 14.05.  A Currie grid might reveal some glazes at cone 6.  But it would be easier to take a cone 6 clear glaze that is close to AL/SI 9 and run a Currie grid on it.


  7. Books are now on order from Amazon, and I've got some test cups going into a cone 04 bisque this weekend. I'll retest my existing mixes on those and see what they do.


    David, does the John Britt books have those limit numbers, or are they something you can email me? What reference numbers are you using?

    I sent an email with the food safe limits, Hesselberth & Ron Roy.  I am using Matrix glaze program.   There is also another book by Michael Bailey "Glazes Cone 6" which has a section on transparent glazes.  I am assuming you have a glaze program, if not I could put in the recipes in Matrix and email you a formula of the glaze for cone 6 .  This could save you time before firing a lot of unknown glazes.


  8. The story thus far...


    Is kind of long.

    I understand some glaze chem at cone ten.  This cone 6 business is a different animal.

    I need a cone 6 clear glaze that is rock hard, food safe (no crazing after a freeze test), compatible with underglazes and Mason stain washes, and  is crystal clear over red clay.  After begging a few recipes from friends and off the internet and doing some initial tests, I've found that the main barriers to hitting all of these points are microbubbles that seem to be present mostly over the red clay indicating the glazes are melting before all the carbon has burned off, boron clouding, and some crawling off of the stain-washed areas. I am cutting my mason stains 50% with gerstley borate, as this has been giving me better brushability than straight frit.  I am willing to alter the stain vehicle as needed.

    I'm not having too much trouble with glaze fit (yay!). My clay body is Plainsman m390, with some use of m370 as a white slip for contrast/texture/better canvas for colours.


    So far, the recipe that seems to have the fewest problems is from digitalfire, the Ravenscrag clear mix of 80% Ravenscrag slip, and 20% Ferro frit 3134. This iteration had some microbubbles over the red clay areas (not the white) and it was suggested to me to flux the glaze out a bit more, after an initial test showed firing with a soak that brought the kiln to cone 7 did clear some of them.  Higher percentages of the frit did get rid of the microbubbles, but brought in boron clouding instead.


    At this point, I'm heading to Insight, because enough with the testing of random recipes. I need to narrow the field before I put brush to test sieve again.



    The only information I could dig up on eliminating boron clouding was from various points all over digitalfire, and pertained to low-fire temperatures. I can only assume that the soloution offered of raising the alumina will apply just as well at cone 6. (unless someone knows of a reason otherwise?)  So boron + not enough alumina= boron clouding.  If I'm sourcing flux from frit 3134 (high boron, no alumina), and the only other material in the glaze is Ravenscrag (a complete glaze at cone ten that needs flux to melt it at cone 6), how to get more alumina?  I already have frit 3110 (high boron, some alumina), but just swapping that out straight across the board actually takes the silica:alumina ratio lower (the boron/silica:alumina ratio stays the same).  So that doesn't fix the problem. So how about adding lithium to replace some of the boron? I have in my posession petalite and spodumene, sources of both Lithium and Alumina.


     Here's where my understanding breaks down. Just as a starting point, if I change the 20% frit from the original recipe from 3134 to 10% 3110 and 10% Spodumene (see screen shot), things look pretty good on paper. The Alumina:Silica ratio is way better, there's almost no boron to cause clouding, the expansion rate seems pretty good, and both frit 3110 and Spodumene begin to fuse at a higher temperature relative to frit 3134, giving the clay body time to off-gas and fix any potential bubble issue.  But have I taken my fluxes too low? How badly is the lithium going to mess with colour response? I don't totally know how to interpret these in relation to the limit formula (pink column on the right). Is anything else seriously out of whack that I'm not looking at?



    There is very good information on clear glazes in John Britt's "Mid range Glazes"  The glaze you are thinking of working with is not in the food safe limits.


  9. I'm a Technical Writer who is interning at an Art Institute in my hometown. I'm writing a biography for an exhibit featuring Daniel Rhodes. I wondered if anyone had any information on what type of philosophies and genres he may have supported and displayed in his art work after he lived in Japan. I find the "Heads" and the "Guardians" pieces to be very beautiful; however, i can't seem to find any information on the philosophy or reasoning behind why he created these. Any interesting facts or comments would be very helpful. 



    There is a preface to his book "Pottery Form" that may be of interest.  I know of the head forms but this was after he went to Japan and I was no longer a student of his.  I will ask my friend Prof. Wally Higgins about this.


  10. Daniel Rhodes studied clay and glazes technically and wrote many books including Clay and Glazes for the Potter and Stoneware and Porcelain. How important do you think his research and studies were to the art of ceramics? What do you feel you have to thank him for in this particular field? 

    Daniel Rhodes was a kind and respected teacher,  I was luckily to be one of his students, before his books appeared.  Another of his excellent books is "Pottery Form"


  11. I thought I would start a new subject line rather than continuing to hijack the other one. I am trying to learn how to do some basic fine tuning of my glaze firing. I am going to start by trying to correct a pinhole issue I am having with one of my more popular glazes. I think the problem is that the temperature is dropping too quickly once reached and "freezing" the glaze before it has time to smooth out and heal over. I have a Bartlett V6-CF controller on my Olympic Kiln and I glaze fire to cone 6.


    With help from people over on the other subject of firing schedules (thank you!) I read through the Bartlett manual again. I read it when I first got it but didn't understand most of what I was reading so bad me for not reading it again. It seemed easiest to simply cut and paste the info from the Bartlett Manual so I don't get it wrong.

    This is their firing schedule for cone 6:



    Then I found this towards the back of the manual concerning a pre programmed vary fire program called User 6.



    They have something called a 16-S (16 segment program) under the menu section on the controller.


    I played around with the controller and was able to turn on this special, 16-S, user 6 cool down program. I do have a question concerning their Important Notes section. I am using the preprogrammed slow glaze cone fire program and the preprogrammed user 6 slow cool program. I don't see anywhere to do the segment adjustment they are saying to do. What am I not getting?



    Once I get the programming figured out my firing schedule should look like this if I am understanding it correctly:

    Slow Glaze

    Cone 6, 2232F

    150 degrees per hour to 250 degrees

    400 degrees per hour to 1982 degrees

    120 degrees per hour to 2232 degrees

    Add on the Vary-fire User 6 Program (user 6 cone 6 cool down)

    Temperature starts at 2232 degrees F then cools at its natural rate to 1900 degrees F

    Then cools at 150 degrees F until it reaches 1500 degrees F at which point it then cools at its natural rate the rest of the way down to kiln opening temperature.


    Am I getting this right? Will adding this onto my slow glaze schedule help reduce pinholes?



    I think you could help the pin holing problem by changing your last ramp to cone 6. Instead of 120 F ramp   go to 80 F ramp than go to cone table and hit cone 6.  The controller will then calculate the temperature required to go at a 80 deg F ramp to cone 6.  You may also find that with this slower ramp you don't need the cool down.

    The final temperature will now be around 2218 F instead of 2232 F.  You can verify this after the firing by hitting the review button.  If you review the program before firing it will say 80 F ramp cone 6


  12. Hey everyone.... Completely clueless but wanting to tweak my firing and have been reading all the lines on firing schedules to educate myself. You guys are fearless with your firing let me tell you!


    I see some are doing a cone 5 with a long hold to get to cone 6 with good results. I was wondering why you don't do a cone 6 firing then program in a hold at a slightly lower temperature to get the results desired. Does this change the results? I think this schedule might fall under a controlled cool?


    Now that I have my test kiln I want to play some with firing schedules since I don't have to risk a whole kiln load while learning.


    Results I am interested in getting.... Less pinholing on certain glazes, improved vibrancy in colors and more of an interesting reaction between layered glazes for some as well. From what I have read this is all possible with firing schedules and I am just trying to figure out where to start.



    You can use a hold at cone 6 but you have to change the top temperature to keep a cone 6 firing .  For example cone 6 at 108  F ramp equals 2230 F, no hold, but a 30 minute hold means you need to change the top temperature by -40 = 2190 F to get the cone 6 to stay about the same.


  13. So I was thinking about glazes and I fire my kiln at 108F/h to cone 5 and hold for 60 minutes. This got me thinking about trying orton's other rate of climb. Trying something like 27F per hour to cone 6 instead of using a hold at cone 5. So fire to 2111F, then climb to 2165F at 27F/per hour. I was wondering if anyone has tried this type of schedule? I am curious at the differences it would make in my glazes. Instead of going straight cone 6, changing to cone 5 with an hour hold improved my glazes a lot. It got me thinking about trying this. 


    Anyone fire at that final rate of 27F/h? Did it improve your glazes or no change? 

    A slower firing will give you improved results.  You should fire to 1965 deg F than change ramp to 27 deg F and fire to 2165 deg F, and use self supporting cones.  The cone tables are based on the last 200 deg F of firing.  You can also use different rates for the last 200 deg F, example 60 deg ramp to 2205 deg F starting at 2005 deg F.  Depending on how good your thermocouple is you should come close to cone 6 down.  You can also change how fast you get to the 200 deg F before changing the final ramp to temperature so that it will not take such a long total time to fire the kiln.


  14. Here is a picture of the new one.



    Just replace the wires on the terminal board just the way they came off.  I wouldn't add any solder to the wires, this will add another dissimilar metal and could introduce unwanted errors in the the readings.  You will just do fine replacing the thermocouple your self.


  15. I'm teaching ceramics at a school with a Geil kiln with an automated controller. I'm in need of instructions on putting it into manual mode. I'm old school and don't like pushing a lot of buttons to get the gas to go up or down. The operating manual for the kiln is extremely perfunctory on how to accomplish this. Could someone instruct me step by step on how to put the controller into manual mode and just run the kiln?

    You should be able to control gas manually by placing the controller in manual mode which then reads the output to the gas valve.  If you don't want to use the auto gas valve then there should also be a hand lever valve near the gas pressure gage.  In that case with the hand valve shut off, put the controller on Manual, set to 100% output than you can slowly open the hand lever valve to get any gas pressure you want.  If you have damper control than you will have to put that controller on manual, or disconnect the linkage and move the damper to where you want it. 


  16. David

    My fiends with old Giels use them with that older Giel DD control to oxidize as well to body temp where it holds until they can dial it Manuel into a reduction. They also dial it so its a fail safe shut off from that body point upward in case they fall asleep.

    I get all that but I thought the original poster here wanted all automated system.

    Sounds like you have your kiln set up like that Giel DD controller now as well.

    Hi Mark,

    If the original post was to fully automate a kiln including oxidation and reduction, than I read it wrong , because this becomes a very complicated thing to do.  Also what kind of burners, venturi or forced air.  As I posted earlier I only use automatic to get up to the body reduction, then I go to manual, which involves gas, air and damper adjustments. Industry usually doesn't want to go into reduction so automatic control is what they use. There should be an easy way to use any kiln in the manual mode if that is want the customer wants.


  17. This is a very old Alpine kiln and I was wondering if anyone is familiar with this kiln and it operation?

    Alpine kilns are rugged and well made kilns, usually found at University's or production potters. The only one I worked on was a larger kiln and had a minor problem with a gas valve.  They have a web site www.alpinekilns.com


  18. Morning all, I love the effect of crystal growth in glazes. I want to experiment making a glaze for electric kiln firing on stoneware to cone 8/9. Can anyone share a recipies?

    Here is a base recipe that works at cone 8 down to cone 9 -15%.  You will have to experiment with colorants. The 3 hour soak range is from 2000 Deg F to 1980 deg F. Allthough porcelain may be the preferred clay I use my stoneware clay and am pleased with the results.  The size and amount of crystals vary with vertical or horizontal surfaces.

    Frit 3110                  53.6

    Calcined zinc Oxide 26.7

    Silica                        19.7


  19. @David:


    The first attachment is when I did a one hour hold. I went past cone 6. 


    The second attachment is with a 50 minute hold.


    These are orton self supporting cones. I don't know where you get that calculation from, but my heat work seems to be accurate with that schedule. I have a little kiln 2.7CUFT. Maybe that has something to do with it? I don't know much about this topic. I just test schedules with cones to make sure everything is right when I change schedules. 


    I didn't post the cone 5 because it was completely flat melted. 


    Maybe I slightly under fired. I dunno, looking at ortons examples of properly bent self supporting that second picture is about dead on, maybe a little less than what they have. Maybe I should go to 55 minutes.

    I am sorry,  I thought you were trying for 1/2 more than cone 6 when actually you wanted cone 6 @ 45deg So you are within 3 deg F of 45 deg.  the calculation comes from Orton Cone Calculation program.  I am glad you use the self standing cones.


  20. I am firing one single cup. The worst yunomi I have made in a while and kept. So plain and ugly. But it will be a good glaze testing cup. Poured the inside with one pour and triple dipped the outside for thickness. I am firing to 2165 with a 50 minute hold, should put me to cone 6.5 then I am dropping 9999 til 1742 and holding for an hour. It will be interesting to see.


    I didn't have time to modify my glaze I keep all my test batches in small 100 containers. My garage literally has over 100+ small containers of test glazes lol. I went and found my modified V's gold and I am firing it now. I will post results tomorrow afternoon. 


    I hope yours comes out good. I would love to have a beautiful tenmoku.


    I think Mountain Meg is laughing at us, she asked for a recipe and we are trying to find one for everyone! haha. lots of great information in this thread though.

    I am curious about firing to 2165 F with a 50 min hold.  Even with this hold you will only get to about 2217 F which is less than cone 6 at a 108 F ramp.  I am missing something?


  21. I cannot wrap around any reason other than mass production to automate firing in a gas kiln.We as potters want to be involved in the process .

    I use the controller to easily get to the body reduction temperature at any rate of rise I want with no risk of going too fast or slow or reducing instead of oxidizing.  From then on it is hands on control of the firing.


  22. Hi All,



    Huge strides and really grateful for so much experience.  We always use new clay for jiggering, not wedged so the cracking would not come from that however, I did compile a list in order of what troubleshooting we are going to do to remedy which I think, combined should work.  Let me know what you think and we're going to keep moving forward, hopefully with no crack!


    1.      Make new molds with 68/70 plaster/water ratio                                                                            

    (We use the pure and simple suggested ratio.  We'll try this instead) 

    2.      Use courser-grog clay body 

    (no grog in the current clay body)

    3.      Jigger an even thickness from center to rim. Perhaps make a new jig or adjust arm accordingly

    (Our rims are much thinner than the center)

    4.      Pop forms off as soon as possible                                                                                                

    (Sometimes we let them sit O/N on the bats)

    5.      Cover when drying.  Perhaps wax edges.                                                                                    

    (We sometimes cover our pieces, depending on the season.  Hot and dry inside this time of year on the E. Coast)

    6.      Jigger each mold 1x/day to avoid saturation.  Dry molds o/n without any forms attached

    (We jigger each mold 2x/day leaving the molds saturated and not able to absorb properly)


    Good times and thanks again!!!


    Best, Ernie

    When cutting off the amount of clay needed for the jiggering, I take a wood mallet and pound the clay down, than finish the slab by running it though a slab roller for the final thickness.  Than place the slab on the jigger mold and starting from the center push it down on the mold with the wheel spinning.  Your molds should not be so wet that you can't get more than 2 a day, which means you must not be using the correct ratio.  I have 12 molds for plates and can get two a day easily from each mold.  The plates shouldn't be forced off the molds they will lift themselves off.  If needed you can pop them off with about 20 psi of air presssure.  Were the plates your design?




    I understand the basic concepts of the controller system for an electric kiln. But how does this work in a gas kiln?  


    If I were to build a control system, I would build a manifold with multiple solenoid valves arranged in parallel. The first line in the manifold would always be open giving a base rate. The next 4 or 5 valves would be attached to a solenoid, each connected to the controller.  The controller would open or close as many solenoids as needed to achieve the desired BTU/hr.   


    Is this correct?

    If so, how many solenoids are in a typical manifold?

    If my idea is off base Teach me how it is done.


    If anyone has a file or diagram to share, I would love it. :D




    I automated my gas kiln which is a Bailey studio down draft 24 cuft and has two burners.  I used a modulating gas valve on the main gas line feeding both burners.  The valve is set so that it doesn't shut off tightly, so the standing pilot is always on,  I also limited how far open it will go so a good air gas ratio is always maintained.  The auto part of the firing is only used up to body reduction when the kiln is then put on manual and the rest of the firing is done on manual.



    This is what I was wanting to achieve by using multiple two way on-off solenoids in parallel.  Once at reduction temp range the air flow and damper would all be manually controlled.  Do you remember the valve manufacturer and serial #?





    The valve is a Maxon butterfly valve, CV-BV series.  The actuator is a Belimo AF-24-SR and the controller is an industrial 4 to 20 MA output controller with a programable ramp rate, Auto/ manual control, type K thermocouple.  It is possible to find controllers as a surplus or used item.


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