You might understand how clay turns from a soft mound into a stone-like substance through heat. But have you ever wondered how ceramic pieces get their colourful glossy finish? Let's dive into glazing to discover the process behind the craft.
What is glazing?
Ceramic glazing is the application of a coating to bisqueware (pottery that's already been fired once) before it's fired again in a kiln.
This coating remakes the piece into an appealing work by adding colour and texture. But it also adds function with a vitrified finish. Glaze starts as a combo of powdered minerals suspended in water that melt and fuse under high temperatures into a hard glass-like surface. It's this glassy coating that makes the stoneware non-porous and food safe.
How are ceramics glazed by hand?
Hand-glazing allows ceramicists to create unique and customized pieces. Unlike mass-produced ceramics, hand-glazed pieces have subtle variations that make each piece one-of-a-kind. The human touch adds an authenticity that connects the hand of the maker to the recipient.
Underglaze
Before we get into glazes, let's rewind and look at a related embellishment that's applied before glaze. Underglazes are a mix of clay and stain as well as adhesives that help the fluid adhere to the clay body.
Underglazes are highly pigmented shades that can be applied singly or mixed to create new shades. They're like paint because they're opaque and stay put, unlike flowing glazes. They still need to be covered with a glaze--hence the term "underglaze". Usually a clear glaze is used to let the underglaze show.
Underglazes are great for adding vibrancy and colour exactly where you want it. In the photo, I'm adding yellow buds and green stems. The pencil marks will burn out in the kiln.
Brushing On
Brushable glazes come in small quantities in pints and gallons. Some potters say you don't exactly paint on the glaze so much as you allow the glaze to flow onto the pot. The trick is to aim for even coverage for a smooth finish.
The main difference compared to dipping glazes is that a gum is added to brushable glazes for good adherence. Often this bubble-free application fires with fewer defects.
Their main appeal is the wide range of colours and visual effects. Most brushing glaze recipes are designed for compatibility for layering to achieve novel effects like variegation, reactivity and metallics. Brushable glazes are also great for detail work. They also allow for the ability to re-qlaze vitrified bisque
This fan-shaped brush is a fave for achieving flow. The glaze is grey here, but will turn into a cobalt blue in the glaze firing! Choosing glazes takes a bit of imagination.
Dipping
Dipping (or pouring and draining) glaze is the fastest method. When applied properly, the glaze should go on perfectly even, with no drips and to the correct thickness. The aim is to achieve a coat that's no thicker than a dime.
Dipping glazes have the advantage of drying rapidly. (Brushable glazes dry more slowly and require a few coats as well as some patience in between the layers.) They're the best option for large surfaces being coated with a single glaze.
To layer glazes formulated for dipping can be more challenging. Unless the base glaze has binders in it, additional glazes may cause the glazes to pull away from the pot. The dried glaze can shred right off onto your fingertips like a flaky croissant surface, but a whole lot less appealing! Also, some glazes contain materials that make them incompatible with layering: in the kiln, the glaze may bubble and gel into an uneven surface.
This beige-toned liquid in the photo below will actually turn into a clear glaze.
The art of the science
Choices to use underglaze before glazing, a single or a combination of glazes, brushstroke or dipping, and even firing temp and length all contribute to the unique beauty of a ceramic piece.
A potter starts with visualizing the combinations that various techniques might produce. Ideally, these experiments can first be tried on test tiles or a smaller sample item. After that, it's in the hands of the "kiln gods" as they say.
What are your favourite glaze combos? Vibrant or earthy? Minimalist or flowing? Are there any shades you love? Let us know in the comments!