PPP: Achieving a Sophisticated Surface
This year the focus has moved from the standard one-dimensional glaze to a more natural, mottled effect. This trend emphasizes the visual impact that is achieved through the surface treatment rather than the form of the product. Sophistication comes from glazes that display movement and dimension, as well as diversity. The traditional glazed surface has been replaced with glazes that mimic the texture of natural stones, polished metals, and the mottled surfaces that were so popular during the Arts and Crafts period in the early 1900s.
The Perfect Finish—Without the HeadachesMany of these finishes can easily be achieved by using the commercial glazes already on the market, commonly referred to as alligator, textured and reduction glazes. Although some ceramists might view the idea of using commercial glazes as going against the purity of creating “from the ground up,” there is a tremendous benefit in using glazes that could otherwise be difficult to achieve.
Most ceramists agree that the creation of a unique glaze requires many trips to the drawing board. Every element of the process, including mixing, blending and firing, must be replicated exactly to achieve consistency. Although glazes that break or mottle are designed to achieve variation, a certain level of predictability is still desired. Glaze companies have tried and tested their formulas and established a level of quality based on their product being mixed to exact standards. For this reason, using commercial glazes will often save you valuable time and unnecessary headaches.
Because electric kilns are the most widely used kilns in today’s pottery studios, it has become necessary to develop glazes that will produce the same unique surfaces seen from gas kilns. Suppliers such as Mid South Ceramic Supply Co., which produces the Opulence glaze line, have reacted to the increased interest in reduction glaze treatments by developing a wide variety of products to meet those needs. While you may prefer to use homemade glazes for some products, you will undoubtedly be able to find a commercial glaze that can achieve just about any surface texture you desire—and in many cases, these glazes might even be less expensive than if you were to make them yourself.
The Importance of ViscosityWhether you are using a commercial glaze or making your own, understanding glaze viscosity will help you better understand how movement is created on the glaze surface. Viscosity is measured when the glaze is maturing. It is during this maturing phase that the glaze smoothes out after it has bubbled during melting. The higher the viscosity, the stiffer the glaze and the less movement it will show.
A glaze with low viscosity may be very runny and pool on a horizontal relief surface, or run on a vertical surface due to gravity’s pull. Coating a surface with a high-viscosity glaze and then layering with a low-viscosity glaze will give your surface depth and movement.
Encouraging Chemical ReactionsBecause the majority of glazes that develop in an oxidation atmosphere result in consistent surfaces, a glaze that renders a textured surface relies on chemical reactions within the glaze itself. If you are using an established glaze recipe, you can add rutile or titanium dioxide for glaze texture. Because rutile contains impurities like iron, it will give your glaze a warm note. Additions up to 10% can be used to break and mottle the glaze.
Crystalline glazes, which are readily available through ceramic supply houses, can also be used to add interest. Some crystalline glazes have a base color with one or more crystals of a contrasting color. The crystals affect the color, opacity and surface texture of the glaze, and are grown during the cooling phase. Holding your kiln temperature at around 1470?F will encourage the growth of the crystals. Because the rate of cooling affects your crystal development, a tightly packed kiln verses a light load will yield different results. The pieces closer to the center will achieve a different look compared to the pieces near the top, bottom or walls of the kiln.
Most textured glazes require two or more coats to achieve dimension and movement.
Revealing Your BodyWith colors that break or mottle, remember that your clay body will also influence your final color. Glazes will break over edges or relief, showing the clay body. Glazing over a piece of red clay will add warm tones to your glaze and deepen the color, while glazing over white clay will give you brighter colors.
The Natural Beauty of EngobesEngobes, which range in color from red to buff, will allow you to achieve a natural surface. Because of its composition, an engobe is classified between a glaze and a clay. Although it fires more vitreous than the clay body it covers, it does not become glassy like a glaze during firing.
One of the benefits of using an engobe is that it can be applied over a wet or dry clay body, and then fired to the clay’s specified temperature. Engobes can be painted, brushed, sprayed and layered. An engobe in a stiffer form can be used to add texture, and after the piece is fired, a stain wash can be applied to highlight the surface. Your wash could consist of a watered-down underglaze, a commercial stain mixed with water or a watered-down iron oxide.
Because an engobe does not fire to a glassy finish, you can seal your piece by rubbing common cooking oil over the surface. This will not only give you a water-resistant surface, it will also add a subtle satin sheen.