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David Woodin

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Posts posted by David Woodin


  1. Soak means a hold at top temperature, but anything over 10 minutes is going to change the heat work by a significant amount and the longer a soak will eventually get you into a cone 6 firing.  You need to be using witness cones to keep track of what is going on.  This is why I would write my own program, because your last segment was at 120 deg /hour.  Unless your kiln has new elements it probably can't go at 120 deg per hour.  The computer controller recalculates the firing based on how fast your kiln can fire within certain limits. My last segment in my user program is anywhere from 30 to 80 deg per hour.  This then means you have to make changes to the top temp because you are firing slower and can get the same heat work. It sounds complicated but isn't.  Are you using a commercial glaze? If you need more information about making a user program than contact me directly.

    David


  2. Ramp is either time to get from one temperature to another or set as degrees per hour.  You mentioned holding for 30 minutes at top temperature, this would mean you probably fired hotter than Cone 04.  Most bisque is at cone 06.  If you fire sculpture or heavy pieces slow bisque is okay otherwise I would use fast bisque and save 3 hours total time.  The Orton 3000 is a great controller and you should look into making your own programs

    David.


  3. All the answers to this are good,  One comment is that the kiln sitter was meant as a safety device for manual kilns.  Somewhere along the line people started to use them to shut off the kiln without using witness cones, which also could cause overfiring problems.  So on manual kilns a witness cone is what you should use to determine when to shut off a kiln. Small cones were made for the kiln sitter.  Most kilns now use a programmer but again witness cones should be in the kiln.to be sure the temperature and heat work were reached.  A 10 min hold for cone 5 will amount to about 14 deg F increase in heat work if the ramp was 108 deg F for at least the last 90 min of firing.

    David


  4.  

    For a  cone 6 glaze the recipe you gave doesn't have enough silica to be within the limits, the glaze doesn't add up to 100% and the fluxing power is very high so it could easily be glossy, the COE is also high which will cause problems on some clay bodies.  That is why a Currie 35 grid test is helpfull, and probably will show several good glazes.

    David

     

     

    Matte glazes generally don't fall within limits.  That was a big lesson for me in 2014.  Limit formulas are mostly for glossy glazes for functional ware.

     

    You are correct.  Michael Bailey in "Glazes cone 6" states that alumina matte glazes are temperature sensitive  and plus minus 50 deg F can make them matt or shiny. So maybe if the witness cones are not the self standing type

    there could be a temperature difference that regular cones wouldn't show?

    David


  5. The Craft and Art of Clay by Susan Peterson is very good, and has some great information about firing kilns.  Since you have a programable kiln you should think about writing your own program.  Look at the Skutt manual about the slow and fast bisque and glaze firings, you may decide that the faster firings will work very well, especially after reading about firing kilns.  You might even want to try single firing which eliminates the bisque firing.

    David


  6. Hi Meg

    If you are having trouble controlling the heat, some questions need to be addressed first. 1. was this kiln meant for natural gas or was it shipped to be used with propane? If there is a nameplate on the kiln it should tell you and also state what the max pressure should be in inches of water column.2. If using propane there should be a regulator on the propane tank set for inches of water column.3. Were the burner cleaned before firing?

    David


  7. Your liner maybe too high in C.O.E.  You could try this one.

    Ferro 3134    15.7

    Custer            17.5

    EPK               18.9

    Talc                 9.2

    Whiting          14.6

    Silica              24.1

     

    total                100

    ziropax               5

    Epsom salts       1

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