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The Colorful World of Majolica: A Beautiful Low-Fire Pottery Glazing Technique
Posted By Linda Arbuckle On June 29, 2011 @ 8:12 am In Ceramics Monthly,Daily,Features,Glaze Chemistry | 12 Comments
Our summer of DVD filming continues and, in a couple of weeks, Linda Arbuckle will be coming to town to share her vast knowledge of the majolica (maiolica) technique on an instructional video. Super excited! If you’re unfamiliar with majolica, it is a type of decoration typically done on terra cotta, with opaque white glaze and colored overglaze decoration.
Linda is an expert on the majolica subject, and shared her knowledge in the written form in the latest issue of Ceramics Monthly. Today, I am presenting an excerpt from that article and in the next couple of months, her instructional DVD will hit the shelves of the Ceramic Arts Daily Bookstore. Stay tuned! – Jennifer Harnetty, editor.
Majolica (or maiolica) in common contemporary parlance is a white, opaque, glossy glaze that is very viscous to the point that it doesn’t move during firing. This allows line quality applied to the raw glaze to be maintained faithfully through the firing process.
The majolica technique is commonly done at low-fire temperatures, although you may work in a similar way on any stiff, opaque glaze at other temperatures with related results. Most of the stain colors used for majolica decorating will fire to mid range (cone 5–6). At cone 10, shino glazes are very viscous and don’t move much, but the available palette of colors is different: many of the purples fire out blue; yellows in reduction are often pale and grayish; most of the pinks burn out; and body stains (e.g. Mason Stain 6020 Pink) may be too refractory even at cone 10. Nevertheless, it maybe worth an experiment or two.
The use of only tin as an opacifier is often modified in contemporary practice. Tin makes a lovely, buttery, very opaque, white glaze. It also increases surface tension in a glaze and may aggravate crawling problems where the glaze is thick (e.g., in corners). Tin in amounts of 5% or above will also cause a color reaction with small amounts of chrome that will cause the tin glaze to turn pink (chrome fuming). This can be delightful if anticipated, but is often not kind to your color plans as a surprise. Many of the green and teal stain colors and some black stains contain chrome, and some rutiles contain small amounts of chrome impurities that can cause chrome-tin pinking in high-tin glazes. For the above reasons, as well as the expense of tin oxide, many artists today use a zirconium opacifier, or a combination of some tin (for denser whiteness) with some zirconium opacifier. This would keep the amount of tin low (say under 4%), yet allow good opacity. Zirconium is weaker than tin in strength, and the usual rule is 1.5% zirconium to replace 1% tin. If chrome-tin pink fuming is a problem, drop the tin a bit, and add that amount multiplied by 1.5 of zirconium opacifier.
Some artists say they enjoy a bit of the terra cotta showing through a translucent white majolica glaze. For me, it darkens the glaze color, damps color response a bit, and makes any thick-thin areas of glaze application more noticeable than a more opaque white. I have always preferred a very white opaque glaze.
Majolica Colorant Suggestions
Gerstley borate production has been erratic, and the material is variable in quality. It pushes decorating colors toward pastel through very fine reticulation (break up) of the glaze surface, and although I used it when I began majolica, I now use frit as a flux (with bentonite added) or commercial majolica decorating colors.
Colorants mixed with only frit settle quickly, have limited brushability, and are very powdery once dry, making wax resist over the color smudge easily. Some artists, like Matthias Ostermann, use this powdery quality to work the movable surface like pastels. The addition of bentonite or CMC gum to the frit and colorant mix aids brushing and hardens the dry surface. Bentonite doesn’t mix easily with water, so be sure to mix dry bentonite, frit, and colorant first, then add water. Some people find an immersion blender handy. I mix small amounts and generally use a tiny whisk. If something is really lumpy, I will use a small test sieve (60 mesh) and screen the mixture.
I use Ferro frit 3124. Others will work, with color reactions influenced by the specific chemistry of each frit. To aid brushability, you may add a small amount of glycerin (drug store item), or a few drops liquid CMC gum to the liquid mix. Too much glycerin or gum can make a very slippery color mix that moves well but doesn’t apply color in an even thickness.
Colors in studio-mixed oxides or stains and commercial majolica decorating colors will generally mix, but some information about ceramic materials helps. I recommend doing line blends of colors to learn more about mixing and relative strength. Copper melts easily, and will color strongly compared to yellow colors. A nice chartreuse may be four parts yellow by volume to one part mixed copper. With paint, yellow + blue = green. In ceramic colors, blue is made with cobalt, a very strong colorant, while yellow may be a stain made with praseodymium or vanadium, which are weaker colorants than cobalt. Equal amounts of mixed yellow and blue decorating colors may still be very blue, due to the strength of cobalt.
This is a smooth, white, opaque glaze that does not move during firing. It may crawl if thick in corners or pinhole over rough-trimmed surfaces. Add ½–3 tsp. Epsom salts to 5 gallons of glaze to flocculate if needed (for less settling and better application). Colorants with flux are usually applied in a thin wash to the raw glaze surface. Fire with a small 03 cone in the sitter to give a large cone 04 tipped to about 2–3 o’clock in front of the peep hole.
1 part colorant, 1 part frit, ½–1 part bentonite:
copper (blue-green), cobalt (blue), manganese (brown to plum with Ferro frit 3110), iron (brown)
1 part colorant, 3–4 parts frit, ½–1 part bentonite:
chrome (grass green), rutile (rusty orange), titanium dioxide (ivory). Most stains are refractory enough to require this ratio.
Note that body stains, like Mason 6020 manganese-alumina pink and Mason 6485 titanium yellow are too refractory for use on top of majolica, even with flux added. Refractory colorants that are not adequately fluxed will result in matte surfaces that are bumpy and/or pig-skinned (crinkled). Testing is the only way to really know.
Cobalt sulfate (blue), copper sulfate (turquoise), manganese chloride (plummy brown), and chrome chloride (green). All are toxic raw. Do not inhale or ingest. They are also absorption hazards: do not handle these without gloves. Soluble colorants are dissolved, rather than suspended, in water, so they wick into the surface of the ware with the water, making a very uniform ground color with a soft edge. If you want any white areas, or to retain clean edges, areas must be waxed before applying soluble colorants. Over-wetting the glaze when applying solubles may move raw glaze and cause color to migrate through the pot wall and/or cause crawling. Too much water on the raw glaze may also cause crawling in the fired glaze.
Some single-coat commercial underglazes work for decorating on top of a majolica base glaze, while others are too refractory. Testing is the only way to determine which ones work. Several companies now make very nice pre-mixed majolica decorating colors. These colors are generally a combination of stains, flux, and vehicles, and they brush well. I suspect that, unlike underglaze colors, the clay content is kept low for more supple brushability.
Both the best and worst thing about majolica glaze is that it doesn’t move when you fire it. Having a decent base glaze coating goes a long way toward being happy with the final product. Additionally, large bumps and voids in the raw glaze will leave evidence of brush strokes on top of them and emphasize your glaze application issues.
Apply glaze in the thinnest coating that will give you opacity, and attempt an even glaze coat. Dampen pieces slightly before dipping to remove any dust and moisten the ware for better glaze pick up. Dipping is my mode of choice, although I do know potters who spray effectively. I want to have a container that will allow me to do one dip of the bisqueware. If I have a piece that will not fit in my glaze bucket, say a long, oval platter, I use a different container for dipping. Garden stores often carry metal or plastic 5-gallon oval tubs. Oil change pans can be useful. I have flexible plastic tubs from a garden store that are wider than my 5-gallon glaze buckets, and will allow me to flex the bucket for longer-than-wide shapes and to form a spout to pour my glaze back into the bucket. In a pinch, I have used cardboard boxes reinforced with duct tape or dresser drawers double-lined with heavy trash bags to hold glaze for dipping.
For errors in glazing (and there are bound to be some) 400-grit wet-dry sandpaper will sand down lumps, or they may be gently scraped down with a sharp knife. When sanding or shaving glaze, do it over a container of water to trap the dust and prevent it from circulating in your studio environment.
Clay Body, Off-Gassing, and Firing Rates
I am still experimenting with firing rates. Several years ago something in clay materials changed and caused gassing in my clay, resulting in many white gas dots in the fired majolica surface, where the base glaze might seal over, but the colorant layer is so thin that it can’t seal and leaves a white spot. Many people maintain that firing slowly is the way to go, and it seems logical that any gas release would be more gentle the slower the firing. On the other hand, I fire many pieces in a small, oval, doll-body test kiln, which cools quickly, and these generally turn out less dotted. The same shapes fired about 200°F per hour in my regular kiln may be more dotted. It’s been an infuriating problem that I continue to research. If you have dotting, try bisque firing as high as you can without making the work too dense to accept glaze. This may drive off gassy materials before glaze application and firing. Bisque at a slower rate, vent your kiln, and glaze thinner if possible. Thinner glaze is less likely to trap the gas bubbles and cause dotting.
|Advantages and Disadvantages of Majolica-type Glazes|
|The viscous glaze does not move when fired. The brushwork stays crisp, with no runny glaze to chip off shelves. Dry-footed areas need less margin on pot bottoms or lid seats.||The viscous glaze does not move when fired, which means any lumps, drips, or pinholes from application remain and do not heal over or smooth out in firing. Thick glaze may crawl.|
|Because the raw glaze absorbs the color from the brush readily and does not move in the firing, the direction of brush marks, speed of the brush, and loading of the brush show in the fired decoration, adding painterly, expressive qualities to the marks.||Because the raw glaze absorbs the color from the brush readily and does not move in firing, direction of brush marks, speed of the brush, and loading of the brush show in the fired decoration, and may reveal hesitancies, touch-ups, and direction of background when painting around motifs, etc., which may distract from the aesthetic impact.|
|Thick glaze blankets the piece, which may forgive small handling errors like finger smudges in the surface.||Thick glaze blankets the piece, which may cover small details in clay handling. like carving or incised decoration.|
|The kiln is a passive tool, resulting in more predictable results from firing to firing. Someone else could fire your work and achieve the same results (easier to share kilns).||The kiln is a passive tool, resulting in uniform color that may look flat or does not describe the form. There are no gifts from the kiln gods.|
|A bright palette of commercial stains gives easy access to a range of pinks, oranges, yellows, and purples that work well with the blue, green, and rust that are available with oxides.||The bright color may look garish, or the entire palette may look too pastel and therefore lose impact.|
|Inexpensive color, because it takes less colorant to put a thin wash on the glaze surface than to color a slip or a glaze.|
the author Linda Arbuckle is a member of the CM Editorial Advisory Board, and is a professor of art at the University of Florida, Gainesville. For more majolica glaze recipes, including a cone 6 version, and additional resources, see her handouts page on her website at http://lindaarbuckle.com/arbuckle_handouts.html.
For more great low fire glaze recipes, be sure to download your free copy of 15 Low-Fire Glaze Recipes from the Pros: Recipe Cards for Low Fire Pottery Glazes!
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