Pompots Posted July 19, 2011 Report Share Posted July 19, 2011 Hello everyone, this is my first post. I was reading some postings and found a great deal of information, so looking forward to participate more; share what i know, and learn more too. I would like to start asking for help with this recipe ^04 High Alcali frit (im using 3110) 75% China Clay 15% Flint 10% add red iron oxide 12% This is a recipe from the book The Potters Palette (Constant and Ogden) This suppose to give a very bright transparent yellow, the problem is i do glaze only for ^5 or ^06 and getting another glaze with a different cone might be an inconvenient or more opportunity to mixed up, so I'm looking forward to reduce the firing temperature of this glaze to ^06 i know adding a "FLUX" can lower the firing temp, i just don't have any idea how much to add, i want to use Nephelene syenite as the Flux, if anyone here knows better, i would appreciate your input. Thanks a lot. Link to comment Share on other sites More sharing options...
Marcia Selsor Posted July 19, 2011 Report Share Posted July 19, 2011 Hello everyone, this is my first post. I was reading some postings and found a great deal of information, so looking forward to participate more; share what i know, and learn more too. I would like to start asking for help with this recipe ^04 High Alcali frit (im using 3110) 75% China Clay 15% Flint 10% add red iron oxide 12% This is a recipe from the book The Potters Palette (Constant and Ogden) This suppose to give a very bright transparent yellow, the problem is i do glaze only for ^5 or ^06 and getting another glaze with a different cone might be an inconvenient or more opportunity to mixed up, so I'm looking forward to reduce the firing temperature of this glaze to ^06 i know adding a "FLUX" can lower the firing temp, i just don't have any idea how much to add, i want to use Nephelene syenite as the Flux, if anyone here knows better, i would appreciate your input. Thanks a lot. I would start by increasing the 3110 a few percentage points and see what happens. The frit is your flux in this recipe. Marcia Link to comment Share on other sites More sharing options...
Pompots Posted July 19, 2011 Author Report Share Posted July 19, 2011 Thanks for your input, i'll try that. Any suggestions on using also Calcium, Strontium, Barium, or Magnesium as lowering temp agents? Hello everyone, this is my first post. I was reading some postings and found a great deal of information, so looking forward to participate more; share what i know, and learn more too. I would like to start asking for help with this recipe ^04 High Alcali frit (im using 3110) 75% China Clay 15% Flint 10% add red iron oxide 12% This is a recipe from the book The Potters Palette (Constant and Ogden) This suppose to give a very bright transparent yellow, the problem is i do glaze only for ^5 or ^06 and getting another glaze with a different cone might be an inconvenient or more opportunity to mixed up, so I'm looking forward to reduce the firing temperature of this glaze to ^06 i know adding a "FLUX" can lower the firing temp, i just don't have any idea how much to add, i want to use Nephelene syenite as the Flux, if anyone here knows better, i would appreciate your input. Thanks a lot. I would start by increasing the 3110 a few percentage points and see what happens. The fit is your flux in this recipe. Marcia Link to comment Share on other sites More sharing options...
Marcia Selsor Posted July 19, 2011 Report Share Posted July 19, 2011 The fluxes you mention are not low temperature fluxes . Try the frit. Frits melt easier at lower temps than the others you mention. Those work better at higher temperatures. Marcia Link to comment Share on other sites More sharing options...
Pompots Posted July 19, 2011 Author Report Share Posted July 19, 2011 Great..Thanks I would let you know the outcome of my tests, it might take a couple of weeks since now im working also in making enough pieces to fill up my kiln for bisque, then the test glazes.... have a great week! The fluxes you mention are not low temperature fluxes . Try the frit. Frits work easier at lower temps, than the others you mention. Those work better at higher temperatures. Marcia Link to comment Share on other sites More sharing options...
Guest JBaymore Posted July 23, 2011 Report Share Posted July 23, 2011 Hi. This particualr glaze recipe is not sitting well within in the more typical Limit Formula for cone 06 leadless glazes. Three things jump out relative to possibly lowering the cone range for me. One is that the alumina number is a bit high. At one level this is good, since alumina helps to impart viscosity in the liquid melt, so it helps keep the glaze from running. It also increases the hardness of the frozen glaze. But alumina is quite refractory also.... so it is raising the melting point of the mix a bit. So dropping that alumina number a tiny bit into the top end of the limits might be a first test to see if that is enough to drop the maturing range enough for you. The "biggie" here is the silica number. It is WAY high for glazes in this cone range. That is good on one hand, because silica provides the "bones" in the molten glass matrix; it is the "strong" element in the glass. The more you can get in there and still melt, generally the better for functional issues like abrasion resistance and leaching. However since the melting point of pure silica is so high, that too tends to raise the melting point of the glaze. So likely dropping that number a tad will also lower the cone range of the glaze slightly. The main sources of of your silica are coming from the kaolin and particularly the flint (which is almost pure silica). So if you were to DROP the kaolin a bit and also drop the silica a bit, you likely will drop the cone range the 2 cones you need. You can think of this as dropping the kaolin and flint, or as Marcia is indicating, upping the frit. In the end, it has the same effect on the resultant chemistry . The glass on the pot is not a blend of the raw materials that went into the glaze slurry...... the kiln changes that raw materials stuff into a glass composed of oxides.... that is composed proportionately out of what the raw materials have supplied into the total mixture. The third possible thought on the cone lowering is to add a tiny bit of Boron into the melt. Boron is a lower temperature melting glass former than silica is........ so it has the "appearance" of acting like a "flux" on a mixture. This could be a small substitution of a high boron containing frit for a bit of the 3110 frit. Testing is important. Have you actually tried this glaze as it is at the lower cone as a test? What are the results? If you haven't tested it yet, we are "shooting in the dark" here a bit. Maybe is is already doing what you want. Maybe not (my guess). Here are the original recipe and a recalculated one analyzed in Insight glaze calc software. I used EPK for the kaolin, "generic" flint analysis for the flint, and an older Frit 3110 anlayis. Current actualy analysis of the materials you actually use would give a more accurate picture.......but likely this is VERY close to the reality of the in-kiln melt. Frit 3110................... 75.00 Frit 3110................... 86.81 EP Kaolin................... 15.00 EP Kaolin................... 9.72 Flint....................... 10.00 Flint....................... 3.47 ========= ========= 100.00 100.00 CaO 0.31* 5.18 5.82 CaO 0.30* 5.68 6.34 MgO 0.00* 0.02 0.02 MgO 0.00* 0.01 0.02 K2O 0.06* 1.82 1.22 K2O 0.06* 2.06 1.37 Na2O 0.63* 11.78 11.97 Na2O 0.64* 13.50 13.63 P2O5 0.00* 0.04 0.02 P2O5 0.00* 0.02 0.01 TiO2 0.00 0.06 0.04 TiO2 0.00 0.04 0.03 Al2O3 0.28 8.60 5.31 Al2O3 0.20 6.95 4.27 B2O3 0.10 2.00 1.81 B2O3 0.10 2.29 2.06 SiO2 3.87 70.39 73.75 SiO2 3.38 69.37 72.26 Fe2O3 0.00 0.12 0.05 Fe2O3 0.00 0.08 0.03 (EDIT: Crap.... the formatting of this forum is not working for that chart and I don't know how to fix it.... sorry) Typical limits range for CaO at this cone is 0.25 to 0.4. As you can see in the first column of each recipe, this glaze sits right in there. Great. calcium oxide helps to make the glass harder. Combined K2O and Na2O is usually 0.38 to 0.47, and this glaze is almost 0.7 on that combination. So this is pretty much a "mono-fluxed" glaze and the characteristics that KNaO imparts will dominate the effects produced to a major extent. This glaze is "outside the norms of typical good glass" in this regard. I'm guessing it will craze on most bodies. And high soda fluxed glazes are not all that durable. Alumina for this cone is normally about 0.15 to 0.25. This original glaze comes in at 0.28...... over the top typical limit. So see above for the lowereing suggestion about this. Decreasing alumina also has the potential negative effect here of making the fired glaze softer...... bad in combination with the high Na2O factor already mentioned. Silica at this cone is usually more like 1.8 to 2.2.......... and this glaze is sitting at 3.87. That kind of silica number is usually seen at much higher cone ranges. So you easily have room to drop this a tad to lower the cone. Again however, this can soften the fired glaze a bit. Now (unfortunately) you also get to the "rheology" of the glaze slurry you have to actually apply to the pot. Decreasing the EPK is going to affect how that glaze stays in suspension and how it "flows" onto the surface of the bisque. So you can "fix" things in the kiln,..... and tend to "break" them in the glazing area. You'll have to test how this works as you adjust the original recipe. One possibility is to add some bentonite to the slurry. Technically this should be re-calculated, but for likely practical purposes you could subsuitute 1% of bentonite for 1% of the kaolin, and not affect the fired chemistry too much, but very positively affect the suspension and flow characteristics. There are certainly other ways to affect the application characteistics, but that is the simplest. Hope this all helps you get more of a grasp on this "tech weeine" stuff. best, .....................john Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.