Porcelain is part of the ceramic family where stoneware, pottery, and terracotta are all family members and are found in many handmade and farmhouse-like home decor. Porcelain due to the types and mix of clays, and specific methods of production, porcelain is a much stronger version of ceramic. There are several finishes that Porcelain can come with - ranging from matte/unglazed to various colored glazes.
Matte and Polished Porcelain
Porcelain has a less than 0.5% absorption rate, a result that classifies porcelain as fully vitrified.
* Unglazed Porcelain - is a type, where the color runs right through the body of the porcelain, with a single color. The color and water absorption rates are consistent throughout.
* Polished Unglazed Porcelain - is shiny, but it does not have a gloss glaze on it, but is polished in the same way that marble or granite is polished, to give them a smooth sheen.
When porcelain is polished, its technical characteristics are being altered, especially its absorption level. The micro-abrasions allow for additional porosity. Because of the finely textured surface of a standard, or matte porcelain, a certain amount of porosity still does exist. Polished and Matte therefore can be exposed as they are water resistant, but their surfaces can be prone to absorb dirt or stains and any soiling would be confined to the surface, and can easily be washed to clean the porcelain.
Considering some background on the types of porcelain drive different characteristics and how you can approach their use and application when it comes to glazing. Not just the type, but also the methods can vary within the type to achieve a particular look and finish. Given that hard paste is the hardest substance in porcelain, the approach, and methods will have some variation.
Hard-paste porcelain (true porcelain) has a more compact and fused body and its fracture is brittle, homogenous, and smooth. This is often used for tableware, and ovenware and where abuse/hard use might be encountered. With the higher firing temperature of hard paste, it may require a second glossed firing to get a uniform and desired to gloss to achieve your end result.
Soft-paste porcelain has a granular fracture, and the exposed portions of soft paste are chalky. Its upper layer can be stained with paint, it absorbs into the soft paste and it is especially used for ornate decorated figurines, vases, and ornaments. Depending on the sourcing and location of the soft paste porcelain manufacturers, for example, St. Cloud factory in France, they have patented their glaze to have a fine satin-like pitting on the surface which set it apart from any other similar glaze.
With Hard-paste the glaze is smooth and slightly fused into the body of the porcelain, and has a uniformly white fine-grained structure. Soft paste also has a high-fired glassy glaze but the structure of the body has a more grainy texture than hard paste.
* Glazed Porcelain - People presume that glazed porcelain means ‘glossy’ or ‘shiny’. However, the word is used in the porcelain industry to refer to the color, or pattern, applied to the surface. The glaze is applied before the porcelain enters the kiln, which fuses it to the surface of the porcelain body, during the firing process. Using the correct firing temperature of your colored glaze is critical to getting the quality and result from you are seeking since underfired or overfiring a glaze can have seriously bad outcomes. Too low it won't be durable and will end up dry and rough, and overfired can deform and melt/runoff on the surface of the porcelain. Using a low-fire glaze on hard paste, the pottery will not be suitable for functional use. Therefore there are certain rules to follow when it comes to using the right glaze for the right temperatures.
* Glaze application - There is brushing which is great for decoration, dipping (submerging) which a lot of manufacturers use, or even spraying the glaze onto the porcelain.
* Overglaze or On-Glaze - this decoration method, is when the colored decoration is applied on top of the already fired and glazed porcelain. It then has a second firing at a relatively low temperature. This produces an ‘enameled’ decoration. The lower temperature of the second firing, allows the colors to fuse to the glaze and allows for a more varied and vivid palette of colors. This enables the use of pigments that will not color correctly at the high temperature required to fire the porcelain body.
Porcelain Glazing is a complex set of variables when it comes to various outcomes. The goal is to have a durable yet decorative product that will be durable and impermeable. How to achieve this, will vary on the application intended on the porcelain - tiles, plates, vases. However, it does add risk to your porcelain product if the process is not well calculated, and the right temperature firing to the paint being matched. Vitreous enamel being used on porcelain is powdered glass mixed with pigments depicts the technique - yet the above details show the variations and considerations between Hard Paste and Soft Paste. We hope this helps understand the differences and how glazing is applied on our products.