Natas Setiabudhi Posted October 19, 2011 Report Share Posted October 19, 2011 Hello guys, I had tried bone china. It's really beautiful, has translucent body even to be glazed. I tried making a cube, dimension are height 6 cm width 16 cm depth 16 cm and and thickness 5 millimeter (bone dry state). There is some problems. I fired it at 1200 C, the shape going to be deform and collapse in the middle of top cube. The shape of cube like upside down box and made by slip cast. What should I do to break the problems. I really appreciate for replying. Thanks... Link to comment Share on other sites More sharing options...
Natas Setiabudhi Posted October 19, 2011 Author Report Share Posted October 19, 2011 Link to comment Share on other sites More sharing options...
Guest JBaymore Posted October 19, 2011 Report Share Posted October 19, 2011 Bone china (heavily fluxed porcelain) is usually fired in special refractory shapes that support the piece duing the BISQUE firing. The BISQUE firing is to the maturity of the clay body....... the piece is fully vitrified. If not supported, a lot of such forms will sag and warp. The refratory "setter" holds the piece in shape. Because it is the BISQUE firing, and no glaze is present, the piece can touch the seter and it does not cause problems. Then after the piece is BISQUED (to body maturity), the piece has glaze applied. Because the piece is alreadty non-absorbent, the typical glazing techniques of the studio potter will not work. So the glaze batch is adjusted so that it can be applied in proper thickness onto an already vitrified body. The piece it then placed back into a kiln, and the GLAZE FIRING takes place...... to a much lower temperature than the BISQUE firing was. So the body is not softening and starting to sag. Somehow potters seem to associate "bisque" firing with a first LOW temperature firing. But one can work with clay other ways than the ones that are typically taught in the "art/craft" pottery field. As to the top surface of the cube sagging.... that is problematic. It can't easily be supported and is a horizontal slab of clay... that is softer in the kiln than it was when wet. So maybe an intertior support wall might help. But that cannot be done easily via the slip casting method. You might have to cast the basic form and then cut and reassemble to accomplish that. Also if you bisque HIGH, without glaze, that MAY help prevent some of the sagging. Sometimes the presence of the glaze layer helps to flux the body more... as well as adding weight to the soft underlying clay wall. It is also a bit of an "industrial design problem". In the sense that it may turn out to be very hard to produce a flat surface cube in this particular medium. The dictates of the medioum may cause you to re-think and re-design the form. best, ......................john Link to comment Share on other sites More sharing options...
Natas Setiabudhi Posted October 20, 2011 Author Report Share Posted October 20, 2011 Thanks for replying.. Ya.. I think must have interior support like you said. What kind of material support for this? Because if made of shaped ceramic, I think it can't stand for longer time. May be one fired, it will crack or broken into pieces. Any alternative materials? and what kind of material added for glazing non absorbent bisque? Link to comment Share on other sites More sharing options...
Chris Campbell Posted October 20, 2011 Report Share Posted October 20, 2011 John & Natas .... What if you bisue fired it on its side in a sagar filled with silica? Link to comment Share on other sites More sharing options...
lynny Posted October 20, 2011 Report Share Posted October 20, 2011 Hi Everything written so far is valuable information. If its a 'box' shape could you fire it upside down filled with calcined alumina? At the bisque (no glaze) stage? Bisqueing to a high temp first and use a low fire glaze is the industry answer to this problem. For a studio potter maybe a rethink to an easier clay body is the answer. I work in porcelain which is finickity too- for difficult forms, I first make a form from raku clay and add 10% zircon flour, then bisque my form with this mould supporting it. best of luck Link to comment Share on other sites More sharing options...
Natas Setiabudhi Posted October 21, 2011 Author Report Share Posted October 21, 2011 Thanks for replying, Ya I think the best for risky clay. we must bisqueing to a high temp first and use a low fire glaze. For my box i think your input deserve to be tried, filled with calcined alumina into the box or put the box into sagar and filled with silica. I just wonder, the supported pieces (raku clay and zirkon) does it stand for high firing? because you said the mould (supported pieces) just for bisque firing meanwhile you use porcelain. Sorry if I miss understood. What kind of material added to the glazes for non absorbent bisque? or may be any other techniques? Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.