For many ceramic artists who may have started with a background in painting or drawing, glazing can be a little frustrating. When you are used to working with paint brushes, pastels, or pencils to create imagery, dipping a piece into a glaze bucket, or trying to paint with glazes that are immediately sucked up by the porous bisque surface can take some getting used to. And then there’s the fact that the unfired color of a glaze is typically not what it looks like fired. That’s where underglazes come in. Underglazes are basically clay-based materials with ceramic stains and metallic oxides added and they come in a variety of forms – liquid, dry, chalks, pens and pencils.
In today’s post, Robin Hopper talks about the different underglaze options available and even explains how to make underglaze pencils, pens, crayons and watercolors from scratch.
For those who are excited about the graphic possibilities of the ceramic surface and enjoy using drawing implements that have something of a sharp, scratchy or linear nature, the marks made by pencils, pens,crayons and trailers likely will make them favorite tools of expression. These tools are the foundation of written or pictographic communication in Western civilization, whereas the brush is the foundation of mark making for most Eastern civilizations. Those raised in the Western traditions usually feel more affinity with scratchy drawing tools than with the soft, calligraphic brushes. Fortunately,the range of ceramic decoration tools encompasses both soft and hard possibilities.
Regular pencils, with what we call “leads,” actually are made from graphite of various degrees of hardness from 6H (extremely hard) to 6B (extremely soft). Marks made with graphite pencils on ceramic surfaces will burn out in the firing, which can be very convenient, as the firing erases the guidelines or grids used for painting or drawing on patterns and designs in ceramic pigments. Guidelines also can be painted on with vermilion watercolor paint, which also burns away.
Pencils for ceramic use (to make marks that don’t burn out in firings) are made with combinations of refractory materials, clays, and colorants and are usually only commercially available in one level of hardness that would probably equate to the HB rating of a graphite pencil. HB hardness is midway between 6H and 6B. Companies that produce ceramic pencils have a habit of coming and going, but most ceramic supply houses usually will be able to find and supply them. Pencils are commercially available in a very limited variety of colors.
Ceramic pencils are normally used on bisque-fired clay that has been sufficiently hardened to withstand the pressure needed for satisfactory mark-making. Since the trailers, ceramic pens, and pencil “lead” may be quite fragile in use, the smoother the clay surface, the better the drawing. Bisque surfaces can be smoothed by sanding with wet and dry silicon carbide or aluminum oxide papers, or the surface of the greenware may be sprayed or brushed with a terra sigillata coating prior to the bisque firing to provide a harder working surface. Ceramic pencils may be used on the ceramic surface just like their graphite equivalent on paper. Although sharpened points tend to wear quickly on the abrasive ceramic surface, the combination of pencil tip marks, side-of-pencil marks, and the opportunity to create tones through finger-rubbing or smudging the soft image gives wide potential for drawn imagery development.
If the commercial underglaze pencils are too soft for satisfactory use, it is quite easy to make your own and harden them to a more satisfactory and less friable state. Ceramic pencil drawings can be fired onto the bisque-fired clay to harden them before glazing, or, alternatively, they can be fired on unglazed high-fired clays, such as porcelain or stoneware, without the need for a glaze coating.
The selection of colorants or mixtures of colorants used in the coloring of the “lead” will control the effectiveness
of the drawings at high temperatures, but most will tolerate cone 10.
To make ceramic pencils and pastels, use a porcelain-type slip with 50 percent white firing ball clay or plastic kaolin. For dry strength in the green state, 3 percent macaloid or 5 percent bentonite should be added.
|Ceramic Pencil Slip Recipe|
|White firing ball clay||50%|
|Add:||Macaloid (or 5% bentonite)||3%|
The materials, including colorants, should be dry sieved through an 80-mesh screen to ensure thorough blending. For color, you can use mineral oxides, carbonates, and prepared stains. A variety of combinations will produce a wide range of colors, although it’s important to select colorants that won’t burn out at high temperatures; not many will, but cadmium/selenium and potassium dichromate are likely to do so. The amount of colorant can be up
to 15 percent. More than that will cause loss of plasticity in the raw state, making it difficult to form the pencils. The more colorant used, the more intense the color.
Mix the dry materials with approximately 45 percent water, to which 1 percent of sodium silicate per 100 grams of dry material mix has been added. This will slightly deflocculate the slip, giving additional green strength while also intensifying some of the colorants.
Form the pencils by drying the colored slip to a plastic state, and then either rolling out coils or extruding lengths of the desired thickness. These then can be left as pencil lengths or cut into shorter 1–2 inch lengths. When dry, fire the pencils to between 1472°F (800°C) and 1742°F (950°C), depending on the desired hardness. A lower firing will produce softer “lead”; higher firing, harder “lead”. The short lengths can be placed in a claw grip drafting pencil (the Koh-I-Noor No. 48 drafting pencil can hold leads up to ¼ inch in diameter).
Pastels normally are used from the greenware state and are not prefired unless they prove too friable for convenient use. To make pastels, use the basic recipe above and simply form the clay into coils or extrusions
to the desired size for use. If they prove too fragile, they can be fired to between 1112°F (600°C) and 1472°F
(800°C) without making them excessively hard. Ceramic pastel drawings should be fired on the ceramic object
to harden them before a glaze is applied; otherwise, the powdery surface likely will be spoiled in glaze application
or handling. Surface powder also might cause crawling through lack of glaze adhesion.
To make wax crayons, mix the dry recipe above with ordinary commercial wax resist. Form the crayon, and let it dry. Since the crayon will contain some latex, it also will have a slight resist effect on the work, particularly when used on bisquefired ware. For a crayon with greater resist qualities, stir colorants into wax, let cool, roll the wax into rods of different widths, and cut the rods in convenient lengths.
Underglaze pens are like super-fine trailers containing an “ink” that gives good flowability for drawing. They are available commercially from a number of producers, or you can make your own with the fine trailers that are available. You can also dip any form of “nibbed” pen, from fine-pointed mapping pens, to quills or sharpened bamboo, into ceramic ink.
|Black Ceramic Ink Recipe|
|Mason Stain 6600 or other black stain||10%|
|Ceramic Watercolor Recipe|
|White firing ball clay||50%|
|Add:||Macaloid (or 5% bentonite)||3%|
A wide range of trailers for slip, ink, glaze or overglaze uses are available from ceramic suppliers, kitchen stores, and drugstores. They usually consist of a rubber or neoprene bulb or container and a nozzle with a fine-aperture tip, or sometimes multiple tips. The simplest to find is usually either a hair coloring applicator bottle or a child’s enema rubber bulb from a drugstore.
Ceramic suppliers often have fine-tipped trailers, sometimes with interchangeable tips of differing aperture. The aperture of the tip required depends on the thickness of the material being squeezed through. Thin inks will go through a fine tip without clogging, but a wide tip may be needed for slips or glazes to flow properly.
As with any tools, you’ll need to practice to get the correct “feel” to achieve the best results. Keep a thin needle tool nearby when working with trailers, because the fine ones tend to clog quite easily.