How to fix a crack in a high fired porcelain piece

After a firing, when you open the kiln it’s not unlikely to find a crack on a piece that you particularly care of, it’s happened to me more than once. Porcelain after the high firing, more than any other clays, is prone to this kind of inconvenience. I work exclusively with porcelain so I’ve found a solution to this firing issue, to avoid throwing away pieces dear to me and which have required several hours of work. I fix the cracks of my objects with a mixture with the consistency of a putty. I prepare it with porcelain powder (previously fired at high temperature), a clear glossy glaze for low temperature and a wood glue in the following proportions:
– 5 g of porcelain powder fired at high temperature (obtained by sanding a dry and still green piece of porcelain), the porcelain must be the same used to make the object that need to be repaired. Once the porcelain powder is high fired, I grind it in a ceramic mortar;
– 2 g of a clear glossy glaze for low temperature if you are repairing a glazed surface, 2 g of a clear matt glaze for low temperature if you are repairing an unglazed surface.
– 3 g of wood glue, it burns during the firing and leaves no residue (it allows to get porcelain powder and crystalline powder as a putty). To get a more uniform mixture of the two powders I add a few drops of water.
Once the repair has been done, I let it dry completely, in this way I’m sure that the surface is smooth, otherwise, I add more “putty” until it is leveled.
I apply with a brush a layer of a clear glossy glaze for low temperature diluted in water on the fixed crack if the surface of the object has a glossy glaze. When the repair is dry, I fire the object at 980 ° C.
I apply with a brush a layer of a clear matt glaze for low temperature diluted in water on the fixed crack if the surface of the object has a clear matt glaze. When the repair is dry, I fire the object at 980 ° C.
I don’t spread any clear glaze if the surface is not glazed and when the repair is dry, I fire the object at 980 ° C.
After firing, the crack will be fixed and waterproof. To camouflage the colour of the repair and make it similar to the surface of the object, I use third-firing colors that I fire at 780 ° C. The third firing colours allow you to imitate the colour of the object’s glaze, even the white of unglazed porcelain. This is possible thanks to the characteristic of these colours that may be glossy or opaque, depending on the surfaces to which they are applied. Anyone wishing to learn more about these techniques can attend my online course ” Glazing techniques, various decorative effects on porcelain jewellery ” in which these topics are deeply addressed.