Ash glazes, with their subtle earth tones and captivating textures, have been a treasured aspect of ceramic art for centuries. The magic of ash glazes lies not just in their rustic beauty, but also in their deep connection to the earth and the transformative power of fire. Using materials created as a byproduct of fire to create glazes fired by fire is a beautiful thing.
But what exactly goes into creating these fascinating surfaces? While ash forms the heart of these glazes, it rarely works alone. Think of it as the lead singer in a band – it needs a supporting cast to truly shine. Silica, typically sourced from quartz or flint, is the main glass-former, responsible for that crucial glassy surface that protects and beautifies the pottery. As help.glazy.org notes, “Silica is the primary glass-former. Without it, you wouldn’t get that hard, glassy surface.” Clay, such as kaolin or ball clay, steps in as a stabilizer, offering alumina that prevents the glaze from running amok during firing and adding to its overall durability. Additional fluxes like feldspar, whiting, and dolomite, which can be found at help.glazy.org, are often added to fine-tune the melting point and surface qualities of the glaze, helping to create the desired effect in the kiln. Finally, colorants like iron oxide or copper carbonate are essential for bringing the vision to life, resulting in unique pottery.
The type of wood used to create the ash also has a huge impact on the final outcome. The selection of wood depends on the desired glaze characteristics. Hardwoods like oak, beech, and birch are often favored for their higher calcium and potassium content, which helps the glaze to become more fluid and glossy. By contrast, softwoods and plant materials with higher silica content are chosen when the aim is to create glossier finishes.
It’s also important to note that the chemical composition of wood ash can vary significantly based on factors such as the species of wood, the soil in which the tree grew, and the conditions under which the wood was burned. As one potter notes, “Some people do burn absolutely pure single wood ash fires… and the chemical composition of the ash of one species is very different from another species… with different results.” Before using it in a glaze, ash is typically washed to remove soluble alkalis that might mess with the consistency and behavior of the glaze. For a deeper dive, explore the art of ash glazes and how they can unlock earthy tones in your pottery.
Firing ash glazes is where the magic truly happens. These glazes typically mature at high temperatures, often between 1250°C and 1300°C (2282°F to 2372°F). Achieving these temperatures allows the ash to melt and interact with the clay body, forming the desired glaze surface. The firing atmosphere is another critical factor, with reduction firing (limited oxygen) often preferred to develop richer colors and textures. Holding the kiln at peak temperature for a period allows the glaze to mature properly. Additionally, the cooling rate can influence the final appearance, with slow cooling potentially leading to the development of crystalline structures within the glaze. A general guideline for firing ash glazes in a reduction atmosphere involves a steady ramp-up in temperature, a soak at peak temperature, and a slow cooling process to promote the development of desired glaze characteristics. Check out the potter’s choice between oxidation vs reduction firing to learn more.
Remember, creating pottery is a journey of exploration and discovery. Like all pottery techniques, working with ash glazes involves specific safety measures. Always protect your respiratory system and skin from direct contact with ash, and ensure you’re working in a well-ventilated space.
And like any other technique, the method used to apply ash glaze—dipping, spraying, or brushing—significantly influences the final appearance of the ceramic piece, affecting aspects such as glaze thickness, texture, and transparency after firing. Embrace the wobbles, celebrate the triumphs, and most importantly, enjoy the process.
