No matter how eager you might be to begin splashing on your newly concocted glazes, there are a few details that must be put in order first. The surface of the clay form must be cleaned of any dust or grease that might spoil the finished object. A large enough volume of glaze or glazes to do the job must be mixed and suitable thickness determined.
The application of the glaze follows these decisions. They will, to some extent, have predetermined the application methods that will be used to achieve the desired result, including brushing, dipping, pouring, spraying, stippling, spattering, sponging, trailing, and multiple glaze applications. Many ceramic artists use various methods on the same piece to achieve a specific effect.
1-2 Brushes and brush marks possible with varied bush shapes, including a hake brush, 2.
Brushing often develops an unevenness in the surface coat, purely due to the nature of the process. It’s generally best done on unfired or greenware, as the ware is less likely to suck the wet glaze from the brush. For this reason, it’s often used for glazing once-fired wares, or if a defined brush quality is required, or if streakiness doesn’t matter. Depending on the desired result and the amount of area to be covered, almost any brush may be used (1), from soft hair watercolor brushes to various types of house painting brushes, or even homemade ones using animal hair.
For glaze brushing where a streaky result is undesirable, Chinese brushes, which have a number of bamboo shafts joined together to make a soft brush up to 6 inches wide, are useful. This type of brush can also be cut into a variety of widths. There are also large, soft Japanese brushes called Hake (2) that function in a similar fashion.
Glaze brushing is usually best done with a well charged brush, so that a maximum area can be covered in a single sweep (3–5). If it’s necessary to go over an area numerous times, there will almost inevitably be a streaky result, unless the glaze itself is sufficiently fluid to disguise the brush marks. If a flat surface is desirable, then brushing is probably not the best way to glaze the piece and you should look at other methods. Household paint rollers, both cellulose sponge and lambswool, may be considered in this instance, as they are less likely to leave a streaky surface, although some texture will probably show.
Dipping wares into pots or buckets of glaze is probably the most common glaze application method. It’s fast, easy, and generally gives a coating of even thickness. Dipping is the most useful glazing process for production work, where speed and efficiency are important. If the glaze runs during application, it can be removed with a knife, if necessary, to ensure a smooth coating for any further painting. Touch up the unglazed spots (from where you hold the piece) with a brush or your fingers.
Pouring and dipping are often done on the same piece of work, where the inside is poured, and the outside dipped. Pouring can be done with a variety of tools, from cans, pitchers and long-spouted pots, to various forms of ladle. All pouring vessels will have their own particular quality of flow, and again, individual requirements will dictate the best tool to use for a particular job. I personally prefer an aluminum pouring vessel with a narrow spout, bought at the local hardware store.
Glazes for pouring should usually be prepared a little thinner than when used for dipping, as there is almost inevitably a certain amount of overlap and excessive thickness can easily cause running of the glaze. Pouring can be used for a wide range of decorative effects, particularly when glazes of different characters and colors are used over each other, and the thickness variations and glaze interaction are used to advantage (6).
Spraying is a good application method, although it usually takes quite a lot of experience to achieve even coatings and to learn to judge the thickness necessary for an adequate covering. It can be used for glazing the whole piece, or for glazing small areas.
Equipment varies from simple to very sophisticated (7). The simplest is the atomizer, made of two tubes fixed at right angles to each other in an L shape and blown through by mouth. Garden sprayers can be used. There are many types of small spray units that utilize a disposable container of Freon gas, with a spray nozzle attached. Some vacuum cleaners have reversible air controls, where spray guns can be attached. There are a wide variety of spray guns requiring compressors for the air control. There are also miniature spray guns, called airbrushes, which also need a compressor to function. These units are comparatively expensive, but are irreplaceable for fine and detailed work, particularly with overglazes.
When spray glazing, much material is lost in the atmosphere as floating dust. Remember that many glaze materials and most colorants are toxic and therefore spray glazing is best confined to a ventilated spray booth, with the glazer wearing a properly fitted respirator.
Most glaze materials are also quite abrasive and are likely to cause severe wear to the nozzles of spray guns. To minimize this problem, carbide spray tips are available. All equipment should be carefully cleaned after every use. Glazes for spraying could also be ball milled to ensure that the particles of material are pulverized as finely as possible. In any case, airbrushes shouldn’t be used for spraying glaze. They’re better for spraying colors, lusters, or enamels, as these are more finely ground than most glaze materials and consequently are less likely to cause problems with clogging or abrasive wear.
Glazes for spraying are normally used in a much thinner consistency than for other application methods. The glaze can have a deflocculant added, such as 1% sodium silicate solution. This will minimize the water content, lower the likelihood of excessive wetting of the piece being sprayed, and prevent washing or flowing of wet glaze from the surface. It’s usual to apply several thin coatings, gradually building up the thickness to give the desired result (8, 9). If the piece is to be glazed all over, particularly when an even coat is required, it’s advantageous to place the pieces to be sprayed on a banding wheel.
Spraying probably wastes more material than any other glazing method. If you’re doing a lot of spraying, particularly with expensive materials, some sort of waste retrieval system might be worth thinking about. The nature of spraying usually results in a broadcast of color. If intricate patterns are desired, masking techniques such as latex, paper, or wax resist should be employed.
Stippling is a form of application done with the edge or tip of a brush, or with a sponge. It’s a good way to apply glaze or color when a broken texture is wanted. The best type of brushes to use for stippling are house painting brushes or artist’s bristle brushes used for oil painting. Care should be taken in the amount of glaze charged into the brush. Since stippling uses the edge or tip of the brush, it’s usually held vertically. If the brush is overcharged, the glaze is likely to run out.
Spattering is more or less a form of spraying, where, because of the nature of the tools used, a broken and uneven spray is achieved. Sometimes bad, inefficient, or worn out spray guns inadvertently do the same thing! The usual tool for spattering is a toothbrush or similar form of stiff-bristled brush (see 7). The bristles are dipped into the glaze and the brush is held near to the area to be sprayed. A knife blade is then pulled across the bristles, toward the decorator or away from the work, forcing them to bend and then spring back, releasing the glaze or color in an uneven spray.
Sponges can give interesting glaze textures (10). Both natural and synthetic sponge can be used to soak up the glaze and apply it to the work. Synthetic sponges can be cut or burnt into patterns, which may then be used to create overall repeat patterns or patterns for simple and fast production. If the sponge is sufficiently fine grained, quite delicate patterns may be made in this way. By overlaying the sponge marks or stamps, it’s possible to develop great depth in the decoration. Although the sponge will deteriorate in time, it will have quite a long life if washed carefully after use.
Glaze trailing (13) is a way of drawing on the ceramic surface in a linear fashion. Like slip trailing, it can be done with a variety of tools. Almost any squeezable plastic bottle with a fine aperture tip will do well. It helps in the cleaning if the bottle or other tool has a removable cap or nozzle. Trailing can be done with a tool made from two pieces of bamboo. A thin length is used for the trailing end, which is joined into a short, fat, bamboo reservoir.
Glazes for trailing are best used in a thicker than normal consistency. In firing, trailed glazes will usually flatten down and spread to some extent. If a detailed drawing is required, it’s often better to trail the glaze on the unfired surface or on a bisque-fired surface before application of the main glaze. Trailed glazes that are applied over other glazes tend to be fragile during handling, as the raised portions are easily knocked off. If the drawing spreads too much in the firing, it might be a good idea to look at alternate techniques such as brushwork or underglaze pencils to develop the required images.
Multiple Glaze Application
Multiple glaze application is often confused with multiple firing processes. Multiple glaze application refers to the use of two or more glazes over each other, which can be applied in a variety of ways to achieve a particular result. It’s usual to use similar glaze bases in multiple applications, as they melt in similar ways and are less likely to cause difficulty in application. However, it doesn’t have to be done that way, and very different glaze bases applied together can provide rich results.
In the application of multiple glazes it’s important that the work is done in a relatively short space of time to prevent one glaze from drying out before the next is applied. If drying does occur, it’s likely that the glazes will flake off or crawl.
Crawling glazes can produce interesting reticulated lizard skin patterns. They occur most often when a glaze with a high clay content is put over a glaze with a low clay content. As the second glaze dries, the clay causes greater shrinkage to occur, and the places where crawling is likely to occur are established.
Glazes for multiple application are generally best used in a thinner than normal consistency, unless excessive running or thick buildup of low flow is needed or desired.
Multiple glazing on vertical forms is likely to present some problems in the firing if the glazes are too thick, because they will probably run. Using thin glazes and minimizing the amount of overlapping at the lower part of the work should help to discourage runs.
Excerpted from Making Marks and The Ceramic Spectrum by Robin Hopper, and published by The American Ceramic Society. These titles, along with Functional Pottery, also by Robin Hopper, are available from the Ceramic Arts Network Shop at https://ceramicartsnetwork.org/shop.