The iron and titanium dioxide particles contained in the gelatinous substance will partially discolor the surface of the body. When the surface of the body is modified (rotary cutting, toning, wiping or trimming, especially in the gap between two plaster molds) it will reveal the faded inner part.
1. The colloidal particles that cause discoloration come from the water in the grouting slurry. The mud that first solidified on the surface of the plaster mold is like a layer of filter paper, which blocks the subsequent colloidal particles in the water flow behind it, causing the color of the surface of the green body to be inconsistent with the color inside. When the clay content in the grouting slurry is relatively high, it is not easy to discolor the grouting vessel, because a large number of clay particles build a microporous system, which prevents the movement of colloidal particles. On the contrary, reducing the content of colloidal particles by reducing the content of ball clay or bentonite in the grouting slurry can also prevent the grouting vessel from fading, or at least weaken the degree of fading to an acceptable range .
2. "Gouting spots" will also cause the grouting utensils to fade. Grouting slurry is a mixture of clay, flux without clay components, and fillers (such as ball clay, kaolin, flint, and gemstones or feldspars in white pottery blanks). Sometimes when pouring the slurry into the mold, the second The point of contact between a strand of mud and the plaster mold is imprinted on the surface of the green body. This imprint is called a "grouting spot". A large amount of oriented clay and mica particles are left on the contact points of the plaster mold. Since the vitrification degree of the grouting spot is higher than that of the surrounding green body, a slight color difference is formed. The grouting spot is in the glaze and It is usually more obvious after firing. The reason is that the degree of vitrification in this part is higher than that in other areas, and the glaze absorbed is relatively small.
The faster the grouting speed, the more obvious the grouting spots, so try to be as close to the mold as possible when pouring the grout into the plaster mold. Put a conical small funnel on the grouting port when pouring the mud. In many cases, grouting spots are unavoidable. In this case, the following methods can be adopted: When pouring grout into the plaster mold, try to keep the contact point of the two close to the bottom of the vessel or inconspicuous.