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  1. Crawling Glazes

    Thank you for your responses. Wondering what your thoughts are on the following additives. Borax and Bentonite The major crawling offender is the Dessert stone glaze base posted below. We use several base recipes. This is just one. The glazes that crawl are taking a long time to dry. When using more than one dipped layer cracking and peeling off in the drying stage is greatly increased. Since I first posted we have tested an addition of bentonite 4%. to the inky black glaze This seemed to help with adhesion and significantly reduce cracking In a separate test, We added 5% Borax. to the dessert stone base....This did two things 1. it immediately thinned out this glaze 2. Cracking was significantly minimized. The addition of Borax did change the fired color and appearance of this glaze a bit. I'm guessing that in the Dessert Stone AGB base there may be a flocculating issue causing us to add too much water to thin the glaze. When testing specific gravity the numbers actually go up when adding water! Desert Stone (AGB) Code # M5 Materials Amt Nepheline Syenite 44.000 43.14% Whiting 16.000 15.69% Flint 15.000 14.71% EPK 8.000 7.84% Talc 11.000 10.78% Zinc Oxide 3.000 2.94% Titanium Dioxide 3.000 2.94% Additions Amt Cobalt 2.000 1.96% Total:102.00 Unity Formula CaO 0.43 MgO 0.23 K2O 0.06 Na2O 0.18 (KNaO) 0.24 ZnO 0.10 TiO2 0.10 Al2O3 0.34 SiO2 2.28 Si:Al Ratio 6.7:1 Calculated Expansion 7.9 LOI 9.0 Cost 1.40 per kg Inky Black Code # G10 Materials Amt Soda Feldspar 15.000 14.29% Ferro Frit 3134 25.000 23.81% EPK 25.000 23.81% Silica 25.000 23.81% Wollastonite 10.000 9.52% Additions Amt #6650 Mason Stain 5.000 4.76% Total:105.00 Unity Formula CaO 0.73 K2O 0.03 Na2O 0.23 (KNaO) 0.26 B2O3 0.34 Al2O3 0.51 SiO2 4.34 Si:Al Ratio 8.5:1 SiB:Al Ratio 9.2:1 Calculated Expansion 6.5 LOI 3.7 Cost 2.36 per kg
  2. Crawling Glazes

    We have 27 glazes in our studio. Some crawl at times. Usually cracking appears on the dried glazed piece as though the glaze is having an adhesion problem. Glazes often get very thick a day or two after mixing and need more water added. I use distilled in mixing and to thin. I'm thinking an additive may help adhesion. Any thoughts?
  3. clear glaze question

    I have used Duncan concepts and tested in a variety of ways. Cone 6, cone 04, single fire, etc. (all worked well!) Although the colors aren't as bright at cone 6 (with Amoco's HF-10 over) they are still nice (greens were a little dull). The concepts seemed to get a bit glossy on their own without a glaze as well. I needed the bright colors for a elementary school outdoor tile mural. so I bisque fired to cone 6 and glaze fired to cone 04 using the LG-10 clear over. It worked beautifully! Bright colors and strength. It has been up for 6 years in WI. winters and looks great. I also like the Amoco Velvets a lot. some colors are not as bright (dull greens mostly and iron reds seem to burn out). I have also tried testing of (1%-30%) additions of Mason stain to my porcelain throwing body and have been very successful. The clear glaze you use will have a great influence on color. Good luck and Happy testing Hang in there.
  4. Opinions on electric Kiln loading

    It has been my experience that when loading a kiln, if the kiln posts are not stacked directly above each other you are potentially gambling with a broken shelf due to the stress. Corners break off all the time if not supported. I have witnessed this when a broken shelf in the middle of a large load caused the domino effect of every shelf beneath to become broken and the entire load ruined.(this was a case of a student not following the rules of kiln loading. Hard lesson learned.) Also, the use of soft brick for posts can cause the posts to stick to the shelf above and make unloading difficult and mar the surface of the soft brick. (unless of course you used a cookie)
  5. I am in the process of testing clear cone 6 clear glazes to fit my cone 10 porcelain clay body. Why this odd combo?(This is the clay I have right now 500 + pounds, when it is gone I may choose to switch to a cone 6 clay and testing will resume again but at least I will know what to do) Clays tend to change over time and I am seeking a clear understanding of glaze formulation in order to be flexible. I am looking to alter my glaze to meet the following requirements. Does this glaze make for a strong durable functional product without crazing? and Does it look nice over slips? My results were mostly good but not perfect. Crazing or Shivering in all tests. Some tiny cracks some large. Q 1. (How can you tell if a glaze is shivering or crazing?) Q 2. When tinkering with a recipe to reduce crazing how do you know when you are getting close to a good fit? What does it look like when you cross the line of fit into the opposite problem? Q 3. What should I change in this glaze to be rid of the crazing or shivering? This recipe was the most successful out of 6 different formulations including 2 Amoco clear varieties. (Very small Crazing) Katie's Clear Nepy Sye 39 Gerstly Borate 27 Flint 18 Whiting 8 EPK 8 2nd runner up....did not make colors look as good. Crazing large crackles. CDG Clear Frit 3124 85 EPK 15 ------------------ Zircopax 2 (for bright colors) *I found little difference in using the pax myself. I love the simplicity of the second choice as well as there is no gerstley borate to complicate the recipe. Thank you for your thoughts.
  6. Sustainability In The Studio

    In the book Making an Installing Handmade tiles by Angelica Pozo, there is a method described to test tile clay for extreme cold outdoor use but also a reasoning for why certain clays work and others do not. (page 126) This is a terriffic book to own. I used this test prior to creating an outdoor tile mural for a school. It was definitely worth the time to test. I found the method printed out on another clay thread From research by Dr, brownell and other Ceramic Engineers at Alfred via Ted Randall, Val Cushing.... From "Cushing's Handbook", 3rd edition "To determine if your clay body is safe from cracking under freezing and thawing conditions, find the C/B ratio by the following lab test procedure. 1. take a sample of your clay body and take the dry weight. You must weigh carefully and accurately Record this weight as D 2. Immerse this sample in water for 24 hours. DO NOT Boil the Water. (just immersion, not boiling or heated water) 3. Take the saturated weight (after 24 hours in water) Wipe off the surface water and weigh carefully.. Record the weight as C 4. Replace the sample in the water (immersed) and BOIL THE WATER. Leave the sample in the boiling water for Two Hours 5. After two hours of boiling, wipe off the surface water and carefully weigh the samples. Record the weight as B 6. us the weights determined above in the following formula: D represents: Dry Weight of fired Test sample C represents: WET weight B represents Boiled weight (1). C-D /D = 'C; value.(i.e., wet wgt minus dry wgt divided by dry wgt gives "C" value (Note that "C" value is different than 'C' weight above) (2) . B- D/D = "B" value. (i.e., boiled weight minus dry wgt, divided by dry wgt gives "B" value (3). "C" value divided by "B" value = "C/B ratio". The final result must be less than 0.78 to indicate that a clay body is safe for outside use in winter, freezing and thawing situations. This is the standard used in the Ceramic industry