Unglazed porcelain is a porcelain product with no surface glaze therefore having the same composition throughout the entire body; this is often referred to as "through-body". This is the originally-conceived form of porcelain tile and might be called the "real" porcelain tile. Through-body porcelain is manufactured as one monolithic tile without surface glazes or finishes. It is characterized by the color pigments being consistent throughout the body of the tile. Originally, the aesthetic look was limited to speckled, "salt & pepper" effects. Recent developments in the production process have made it possible to mix various color pigments so that random swirls and veins of color, similar to natural effects, can be produced. Unglazed porcelain provides the highest abrasion resistance due to the fact that the complete body of the tile is the wear layer; the tile exhibits the same properties throughout their thickness. Basically, the aesthetic features of unglazed porcelain can be achieved primarily by three different methods:
Applying soluble chemical salts to a through-body porcelain bisque prior to firing. Applied using multiple silk screens, spray machines or brushes, the overall aesthetic effect can be quite varied. Suspended in an aqueous solution, these metal salts penetrate into the unfired tile body. After the tile body dries, the tile is fired during which time the metal oxide salts react with the porcelain body resulting in various colors. This type of porcelain is classified as unglazed since the salts are not considered a monolithic glaze. Single powder (dry powder) charging is the production process by which charging of colored powders in the press cavity create the aesthetic beauty.
Double-charging (or double-loading) process is similar to the single powder except that a second loading of very fine colored powders is applied to the surface creating the aesthetic beauty. Double-loaded porcelain is manufactured with two layers of porcelain pressed together and then fired. The top layer is approximately 1mm thick and is pressed to the base porcelain layer under high pressure. This top layer is comprised of porcelain clays randomly infused with various color pigments that create an infinite range of color combinations and patterns emulating that of natural stones. This bonded porcelain ‘sandwich' is then fired.
Polished or semi-polished - After the production stages, the tiles undergo a polishing operation similar to the process for polishing marble. A few tenths of a millimeter of material are removed by polishing wheels producing a surface with a mirror-like finish identical to marble or granite. In a semi-polished product, the tiles undergo the same process, however the highly textured surface means that only the "high" areas are polished.
When selecting porcelain tile, it is essential to specify the correct installation materials and methods. By ISO definition, glazed and unglazed porcelain must achieve 0.5 percent or less water absorption. This low porosity rate challenges a bonding material's performance. so Therefore, a premium latex modified mortar system is strongly suggested.
Bottom line - porcelain is so dense and tightly pressed that it will withstand much more pressure, loading and impact than any other product installed on the floor today. Porcelain tile is produced using the finest natural ingredients combined with a rigidly controlled manufacturing process that utilizes the most advanced processes and technology. Porcelain outperforms even granite for years of low-maintenance looks that last.