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David Woodin

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Posts posted by David Woodin


  1.  

     

    excuse me for butting in, but this looks like a cratering glaze.  a deliberate attempt to look exactly the way your picture is.  what is the recipe you found and what was the description that made you want to try it?

     

    i made the mistake of trying some glaze recipes without knowing how they would turn out.  the ingredient list will tell one or all of the glaze experts here if that is what caused this. 

     

    these are definitely not pinholes.

    This glaze doesn't come close to cone 6 limits and probably is boiling, hence the cratering.  Try it on a pot you are bisquing and see what happens, in other words it is like a cone 04 glaze with the amount of flux it has.

    David

     

     

    Hello David, thank you for the comment. I will give that test you mention a try if they allow me where we are firing. Strange than, that the author writes it's for cone 6 to 8

     

    I am going to do a bisque firing shortly so I will try the glaze at cone 06 and let you know what happens.  If you are looking for a satin matte that covers the range of cone 6 to 8 than you could try this one:

    Ferro frit 3134      12.1

    Custer feldspar      5.7

    EPK clay               40.4

    Talc                      14.1

    Wollastonite          20

    Silica                      7.7

    Total                    100

    David


  2. excuse me for butting in, but this looks like a cratering glaze.  a deliberate attempt to look exactly the way your picture is.  what is the recipe you found and what was the description that made you want to try it?

     

    i made the mistake of trying some glaze recipes without knowing how they would turn out.  the ingredient list will tell one or all of the glaze experts here if that is what caused this. 

     

    these are definitely not pinholes.

    This glaze doesn't come close to cone 6 limits and probably is boiling, hence the cratering.  Try it on a pot you are bisquing and see what happens, in other words it is like a cone 04 glaze with the amount of flux it has.

    David


  3. Marcia,

     

    For my glaze firings I fire to cone 5 and program in a 15 minute soak, for bisque I do not program a soak.  Even with the soak, the clay is not vitrified.  I hate to raise the cone in the program in a glaze firing because my clay is very susceptible to bloating above cone 5.   

     

    Cavy,

     

    Mine is Betsy!  :-)

    Check to see if you have an offset programmed   for the thermocouple, go to the options sections and get to TCOS a 90 before the number will raise the firing temperature OO will decrease the firing temperature.  You shouldn't need to soak for 15 minutes.

    David 


  4. Okay, I see what you mean now. 

     

    I try to keep my pats under 1/4" thick, which I suppose is why it's never been an issue for me.  Is there an accepted thickness for a clay pat?

    If you make your pads 3/8" thick and do what you now do you will have a cone 2" above the pack.  I f you want taller packs that is okay but not as easy to get the 8 deg angle.  There is a symbol on the cone and its horizontal line is 2 " the top of this symbol is 1 3/4 inches so that is your guide for the proper depth to have the cone above the cone pack.

    David


  5. So after 16 .5 hours and no change in witness cones I shut the kiln down. All shelves fired to a perfect cone 5.  The tests needed to be cone 6. I am going to check for a broken element , but  I believe I need to replace the elements. I  won't have time to get them and change them out before my class. Would it be foolish to try to fire another batch of tiles at a faster rate ?  I was thinking that if I fired faster I might get the extra heat  to get to cone 6. Would I be wasting my time to try again? 

    You will be wasting your time, fix the kiln first.

    David


  6. I find that the best way to set cones in a cone pack is to press the base of the cone to a flat surface, so that the cone takes up the precise angle it was designed for.  Then move it to the clay pat and press it in, keeping the angle the same.

    That is fine for the angle but the height is also critical.  The box doesn't tell you the height but the Cone table says if 1 3/4" use self supporting table, if 2" use the large cones table.

    David


  7. As everyone has said cones show heat work, thermocouples read temperature at its tip, but you can corelate all this information and get good firings with controllers. The ceramic Industry uses controllers but always have cones in each firing.  Self supporting cones are very accurate but cost more.  Large cones are only as accurate as how they are set in the cone packs, so read what it says about setting cones on the Orton box.  The base of the cone is cut to the correct 8 deg angle.

    David


  8. The Currie method is great for revealing what other glazes you might have in the grid from a known glaze.  So he takes a known glaze and makes extreme changes in the Alumina/ silica.  But if you want to make a glaze from scratch take a look at Robin Hoppers book "The Ceramic Spectrum"  The information I posted was a method to look at two colorants and actually uses the same % as the Currie grid after you make the 4 corners using a known glaze.  You don't do anything with the alumina or silica.

    David


  9. If you want any accuracy  or repeatability you need to realize a regular switch is going to give you all kinds of weird readings, drift with temperature changes etc., this is because every connection is different material and will in turn act as a thermocouple.  A reasonable way to keep the accuracy of what you now have is to put a thermocouple recptacle on of near the panel meter and t/c plugs on the thermocouple extension wire and plug the T/C you want to read into the T/C receptacle.  Look on www.omega.com  search for part number RSJ which is a panel receptacle from $2.45 to $5.00, search for part number OSTW-CC-K-M which is a plug $2.95.  If you don't care just put in a cheap switch.

    David


  10. Is this a common occurrence?    I just replaced a relay switch and tested elements to make sure that was the problem.  Then I turned on kiln again and temp read -320 degrees.   I have the cheaper S type thermocouple on this kiln, which is only used to bisque.  Kiln is almost 2 years old.  Didn't realize thermocouple could turn black ... guessing it needs to be replaced?

    Look at the picture in "Thermocouple spitting metal flakes" post.  If that looks like you thermocouple than you have a type K.  Usually a type S would be in a ceramic protecting tube.

    David


  11. I have been using the variants of leach clear that appear in the John Britt high fire glaze book. This is the base recipe

     

    40 Custer Feldspar 

    30 Silica or Flint 

    20 whiting 

    10 EPK Kaolin 

     

    Does anyone have recipes using this base they would like to share. The book includes a white using zircopax, a green with iron and a temmoku. I have been thinking of subbing yellow ocher for the EPK.

     

    thanks in advance for sharing 

    This glaze would be a good glaze to try doing a Currie blend on.

    David


  12. The figures I gave you are for self supporting cones or large cones mounted @1 3/4 ". Large cones mounted with 2" mounting height deform approximately 2 deg C lower.  As to your other question All the figures are based on the last 100 deg C of firing, a 40 deg C ramp to 1159 deg C should bring cone 4 down Its starting point is 1059 deg C.  A 30 minute hold means you subtract 25 deg C from the 1159 deg C = 1134 deg C is its top temp., its starting point is 1034 deg C. So with a hold you fire longer at a lower temperature.

    David


  13. I usually make a 20 grid but 35 grid would work fine. A = base glaze + 8% Iron Oxide: B same base glaze + 8% Iron Ox.& 10% rutile;

    C same base glaze no colorant: D 10% Rutile.  This gives a line blend from A to C for iron; A to B iron stays at same value but it cross blends with Rutile :C to D line blend for Rutile: This line blend cross blends with iron B to D.  This is impossible to explain but the top row 1 thru 4 Iron is 8%, but 2 to 4 rutile is #2 = 3.33%R + 8% Fe,# 3= 6.67% Rutile + 8% Fe, # 4= 10% Rutile + 8% Fe.  Anyway it is a good method for testing 2 colorants and depending on your base glaze you may get some rutile blue. take a look at www.matrix2000.co.nz

    David


  14. David, does the CD give the temps for firing to cone 4? I'm looking for the temperature I need to reach if I fire the last 200oF at 72oF / 40oC per hour.

     

    Ideally I'd like to know what temp to reach if I fire at this rate and have a 30 minute hold, but any info will be useful.

    cone 4 @72 deg F ramp is 2118 deg F top temp. a 30 minute hold is -45 deg F. ( reduce the top temp by this much) or 40 deg C  ramp to 1159 deg C top temp. 30 minute hold -25 deg C cone 4 down 90 deg.

    David

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