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Cone 2: Develop a glaze and engobe to make stoneware from terra cotta bodies
This is ongoing testing. The engobe is meant for additions of stain and application at leather hard stage to the dolomite-based Snow, then drying, bisquing and clear glazing.
Project Name Engobe for Low Fire Dolomite Body Project Codenumber UnAssigned Notes The Plainsman Snow clay body (based on the L4410P recipe) fires pure white at low temperatures, making it an ideal base for bright-colored glazes. However, since it contains significant dolomite, it can react with some glazes (e.g. making clear glazes cloudy). In addition, it can be desirable to decorate and color ware at the leather hard or dry stage, bisque, and then dip ware in a transparent glaze. For these reasons, an engobe that works with the body is desirable. |
Brown Engobe for Snow
Total:112.00 Notes *This is version 1 of an engobe to enable customers to color Snow clay (code number L4410P) at the leather hard stage and just finish with transparent on bisque ware. Pictures L3685Z5 engobe on Plainsman Snow clay at cone 04 Glaze is G1916Q3. L3685Z6 on snow with G1916Q3 glaze - Closeup It is difficult to tell if the cloudiness is bubbles or crystals. Testdata SHAB - Shrinkage/Absorption
XML (to paste into Insight) <?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="Brown Engobe for Snow" id="213699" key="XgsW52Pv" date="2022-03-18" codenum="L3685Z6"> <recipelines> <recipeline material="Wollastonite" amount="20.000" tolerance=""/> <recipeline material="New Zealand Kaolin" amount="55.000" tolerance=""/> <recipeline material="Silica" amount="25.000" tolerance=""/> <recipeline material="Ferro Frit 3110" amount="5.000" tolerance=""/> <recipeline material="6100 Mason Brown Stain" amount="7.000" added="true"/> </recipelines> </recipe> </recipes> Born: 2021-03-08, Modified: 2022-03-18 13:38:57 |
Cone 04 Brown Engobe for Snow
Total:113.00 Notes *Based on L3685Z6, addressing a number of issues. This is the best engobe so far for using on Plainsman Snow at cone 04 (40% dolomite, 10% Nepheline, 50% ball clay). Pictures Four cone 04 clear glazes cover L3685Z7 engobe differently These are Plainsman Snow (the L4410P recipe) cast pieces with L3685Z7 stained engobe on the upper sections. The four sides have been clear glazed with Mayco S-2101, Duncan PB001, Amaco LG-10 and Spectrum 700 transparent glazes. The left half of each has an extra glaze layer, that has not made much difference in any of them. The S-2101 transmits the brown color best, the LG-10 and PB001 a little less. The 700 is decidedly lighter, it is altering the brown color (likely MgO in the glaze is reacting with the stain). However, over the white body, the 700 is by far the best, being crystal clear and glassy smooth. The lower halves of these also demonstrate something equally interesting: The ones that don't alter the brown do react with the MgO in the white body, yellowing it and turning opaque. The lesson is to try various brands of clear glazes over underglaze decoration and colored engobes, especially with dolomite-based low fire bodies. It might even be advantageous to use one brand on the insides of pieces and another on the engobe or slip-decorated exteriors. L3685Z7 engobe vs Plainsman Snow BiClay bars BiClay strips with Snow dried flat but curled 13mm toward Z7 at cone 05 and 15mm toward Z7 at cone 04. L3685Z7 Snow interface I dropped the BiClay bars onto cement and they were very strong, they did not shatter (indicating no residual stresses within). The bars broke at right angles except when struck with a hammer. Even when breaking on an angle, the join never failed in preference to any other plane. Snow with L3685Z7 engobe at Spectrum 700 clear When thin the glaze is not reacting as much with the engobe. It appear the engobe is creating cloudiness in the glaze, perhaps micro-crystals or micro-bubbles. L3685Z7 fired bars Testdata SHAB - Shrinkage/Absorption
XML (to paste into Insight) <?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="Cone 04 Brown Engobe for Snow" id="213989" key="dBqF7qgW" date="2022-08-25" codenum="L3685Z7" location="BOX 54"> <recipelines> <recipeline material="Nepheline Syenite" amount="23.000" tolerance=""/> <recipeline material="Tile #6 Kaolin" amount="47.000" tolerance=""/> <recipeline material="Silica" amount="20.000" tolerance=""/> <recipeline material="Ferro Frit 3110" amount="5.000" tolerance=""/> <recipeline material="National Standard Bentonite" amount="3.000" added="true"/> <recipeline material="Mason 6100 Stain" amount="15.000" added="true"/> </recipelines> </recipe> </recipes> Born: 2014-11-04, Modified: 2022-08-25 08:55:42 |
L213 40:10 Dolo/NS
Total:100.00 (R) Notes *This is a low temperature, white firing body to replace tranditional talc:ball clay bodies. We have done many previous tests that indicate that 40% dolomite is needed. That being said, glazes have been fitting well enough we are testing 35%. Pictures L4410P - Mayco S2101, Duncan PB001, Spectrum 700 Fired cone 05. No crazing after weeks on any of them. The 700 glaze fires much whiter than the Duncan or Mayco on this body (it must be using a higher quality frit). Spectrum 700 on L4410M, N, P, Q - Cone 05 No crazing out of the kiln on any of them (these of some of the many recipe tests we did before settling on the P version). This is a testament to how good of a glaze the Spectrum 700 is. It fires more transparent (therefore whiter) than the others and fits better. L4410 after several days soaking in water The water as wicked up the walls (between the glazed inner and outer surfaces). After several days there is no crazing with Spectrum 700 or L3879C. L4410P at cone 05 with Spectrum coloured glazes These are slip-cast pieces. L4410P at cone 06 (back), cone 6 (front) Engobe is AMACO velvet. This clay sags and warps at cone 6 yet does not bloat and still has good fired strength. These pieces are slip cast. L4410P fired bars From cone 6 and 5 (top) down to cone 06. L4410P sealed and unsealed The body has high porosity, but this has an advantage: It soaks up silicone sealer very well. The slip-cast piece on the left was sealed (you can see the surface sheen) and it is impermeable to water penetration (the glaze is not crazed so water cannot penetrate there either). The piece on the right soaks up water readily (on the lower unglazed portion). Bonding test of Spectrum 700 on L4410P This GBBT test indicates a very good glaze-body interface. L4494 fired bars This is L4410P with 4% iron oxide added. Bars are fired from cone 5 (top) down to cone 06 (bottom). G3879C on L4410P dolomite body at cone 04 The outside glaze is Spectrum 336. The G3879C is our recipe, a base transparent that we have been tuning to reduce the thermal expansion as much as possible to fit our 50:40:10 BallClay:Dolomite:Nepheline body. The result is glaze compression, it is now under enough compression on the inside of this piece that it is forcing it apart. Testdata SHAB - Shrinkage/Absorption
LDW - LOI/Density/Water Content
XML (to paste into Insight) <?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="L213 40:10 Dolo/NS" id="208137" key="cGkXKWyG" date="2024-11-19" codenum="L4410P"> <recipelines> <recipeline material="KT #1-4 Ball Clay" amount="50.000" tolerance="" unitabbr="GM"/> <recipeline material="Dolocron 413" lookup="Dolomite" amount="40.000" tolerance="" unitabbr="GM"/> <recipeline material="Nepheline Syenite" amount="10.000" tolerance="" unitabbr="GM"/> </recipelines> </recipe> </recipes> Born: 2021-10-28, Modified: 2024-11-19 02:08:24 |