Types of pottery glaze for ceramics

by yuvaporn t

In the ceramic work, one of the techniques that makes the workpiece come out beautifully and remarkably different is the use of glazes to add details. Nowadays, there are many types to choose from. Today Pottery Clay has summarized them here so that potters can select it according to their preferences.

Clear Glazes (Clear Glazes/ Transparent Glazes)

It is a glaze used to coat the product and then act as a transparent glass that is applied to the surface of the product to be transparent until the color of the clay or the color decorated on the surface of the clay can be clearly seen. It is commonly used to coat products that are decorated with colored writing under the glaze or products decorated with colored clay. The transparent coating acts like a thin, clear glass that is plastered on the surface of the product which maybe with or without color.

But if it is a transparent coating that has a color, it is commonly used to coat over decorated containers by scratching or carving patterns in order to make the carved patterns appear beautifully with clear patterns. In addition, clear glazes can be made at any temperature depending on the formula of ingredients used to make the glaze.

Opaque Glazes (Opaque Glazes)

is a glaze that can completely cover the surface of the clay. It is commonly used with stoneware products that do not want to show the color of the clay. The opacity of the glaze is caused by the raw materials that are the ingredients of the glaze with the ability to absorb light and not allowing light to penetrate through the glaze causing the glaze to completely cover the color of the clay. These substances are called opaque substances which include tin oxide, antimony oxide, chromium oxide, zinc oxide, and zirconium oxide, etc.

Luster Glazes (Luster Glazes)

is a glossy glaze. Shining like the skin of a mother-of-pearl shell inside. The key ingredients are lead that ensures good melting and gives the coating a glossy finish. Therefore, it is suitable for coating beautiful décor items only and it should not be used to coat food containers.

In order to use a pearl glaze potters have to be especially careful because the glaze is quite fluidity so it may damage the workpiece and the workpiece plate inside the kiln. There are 2 types of pearl glaze that are commonly used:

  1. The aqueous glaze type fired at a temperature of 1,180-1,200 °C
  2. The color on the glaze type called 'Pearl color' The product must be white glazed or clear glazed and fired at a temperature of 1,200-1,230 °C and then plastered with pearl color and fired again at a temperature of 750 °C the same as overglaze decoration

High Fire Glazes (High Fire Glazes)

are glazes fired at a temperature of approximately 1,230 – 1,460 °C , with feldspar and limestone as the main raw materials to help melt the glaze together with silica and kaolin. It is commonly used to coat porcelain and stoneware products. The coating is strong and resistant to scratch, acid and alkali corrosion. It can be fired in both oxidation and reduction atmospheres.

Intermediate Fire Glazes (Intermediate Fire Glazes)

It is used to coat Earthenware, Bone China and Stoneware. The coating is less rigid than the high power coating but it can reduce the cost of firing and make fresh glazes. It is quite popular among glazed work of sanitary ware, tableware and decorative products, etc. If coating at a temperature between 1,180 and 1,200 °C ,frit is used as a melting aid in the glaze recipe. However, if coating at a temperature between 1,200 and 1,230 °C , basic oxide is preferred as a melting aid in the glaze formula of more than 3 types as it will help to incorporate the glazes and melt well.

Raw glazes (Raw glazes)

It uses natural raw materials such as feldspar, silica and limestone, etc., which can be mixed into glazes without having to make frits first

Bristol Glazes (Bristol Glazes)

It is a result of an attempt to lower the boiling temperature of the porcelain glaze and maintain the strength of the glaze by using zinc oxide as a key melting aid in place of calcium oxide. The glaze has good fluidity and bright colors. Most of the glazes are used to cover the surface color of the clay but if too much zinc oxide is used, it will give the opaque glazing a white and shiny appearance.

Low Fire Glazes (Low Fire Glazes)

Glazes that are fired below 1,100 °C . Most of which contain lead or borax as the main melting aid in the glaze because the clay fired to the point of ripening the coating is less hard making it not resistant to scratches, acid and alkali corrosion. It has high gloss with bright colors and limited firing temperature range. If fired beyond the set temperature, the glaze will flow a lot and may damage the workpiece. It is commonly used to coat roof tiles, art and raku works, etc. It should not be used to coat food containers because food residue can fall inside the cracks of the glaze

Matt Glazes (Matt Glazes)

Glazes that have a smooth matte surface. The coating will not be shiny and does not reflect light or a semi-matte, semi-glossy surface with a slightly shiny finish, or a matte finish with a rough surface. The glaze can be fired at any temperature and can give a matte finish in a variety of ways. No matter it is

  1. Matte glazes produced by adding alumina to the glaze, called “Alumina Matte Glaze”
  2. Matte glazes produced by substituting Flux with barium carbonate, called “Barium Matte Glaze”
  3. Matte glazes produced by using a certain substance in excess of the normal amount and then fired until the glaze cools down slowly
  4. Matte glazes produced by the use of zirconium silicate together 10-15% with talc 8-15 % in the glaze formula to help accelerate the glaze crystallization into granules on the coating surface.
  5. Matte glazes produced by the use of magnesium carbonate in the glaze 15-20% in order to have a matte finish because magnesium carbonate is highly refractory.

Crystalline Glazes (Crystalline Glazes)

Produced by the crystallization of some substances that are separated and become visible. It looks like a large or a small dot or as needle-like lines stacked in or on the glaze. The crystallization of the glaze occurs when the glaze is cooled under specially controlled conditions. The raw materials for crystallization are zinc oxide and titanium dioxide together with the crystallization time and the cooling time of the crystalline glaze. They can be separated according to the nature of the crystal as follows.

  1. Crystalline glazes that cannot be seen with the naked due to the fact that the crystals are so small but so densely formed that they are visible to the naked eye as a matte or semi-glossy surface. It is called a matte glaze
  2. Crystalline glazes that can be seen with the naked eye. It is a crystal that occurs within a glaze or a glaze surface, including Aventurine Glazes (Aventurine Glazes) or gold sand glazes that are large enough to be seen by the naked eye. The appearance of the crystals will look like small scales within the glaze, or it can be small and large stacked.
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