This studio is used for glazing both earthenware and stoneware bisque. It is also used for hand building. The studio has a large 12' x 6' table that is used for these endeavors. Earthenware is a clay that is fired at about 1900 degrees Fahrenheit. This causes the clay to become hard and unable to dissolve in water. However it can absorb water into its structure. Earthenware is not as hard as stoneware. Stoneware is fired at approximately 2200 degrees Fahrenheit or higher. Firing at this temperature causes the clay to vitrify which forms a crystalline structure in the clay making it very hard. Stoneware will not absorb water.
Both earthenware and stoneware are usually fired twice. The first firing is called the bisque firing and it makes the clay hard so that it can be handled as it is decorated. The second firing is called the glaze firing. The glaze firing is when the glass like surface is created on the piece. It is also when the final color of the piece can be seen. Colors can be put onto a piece when it is a clay, when it is bisque as underglazes, or in the glaze that creates the smooth glass surface.
Table for Glazing, Painting, and Hand Building
For earthenware we use Gare glazes. Gare is a glaze and bisque manufacturer that is located in Massachusetts. We tested glazes from 3 manufacturers and decided on the Gare line of commercial earthenware glazes because they are in New England (and therefore local). Also their glazes gave much more vibrant colors than the other two lines we tested. All glazes that are used are non-toxic and are food safe once fired. The Gare glazes include the following:
- Fun Strokes Underglaze - underglaze is painted onto a piece of bisque giving the piece, once fired, vibrant colors. To get a solid color you put on three coats of the underglaze. Fewer coats give transparent colors. The underglaze is covered with a clear glaze by dipping the piece in the glaze. The piece is then fired giving a glass like covering through which the underglazes show. Underglazes come in approximately 50 colors: reds, greens, blues, yellows, purples, browns, white, black, and various other colors.
- Dazzle Dip transparent glaze - a clear glaze which pieces are dipped in after underglaze painting. Pieces are fired once they have dried. After firing Dazzle Dip is clear and glass like (it forms a glass which is similar to window glass but not exactly the same).
- Pottery Glazes - Glazes that give colors that are similar to stoneware glazes, not as vibrant as underglazes but similar to colored glazes used on pottery for the last few centuries. These are used instead of or perhaps in combination wtih underglazes and Dazzle Dip.
- Crystal Glazes - form crystals which fired on the piece. The crystals are present after firing giving very beautiful decorations on the ceramic.
Earthenware figurines these days are often painted with acrylic paints rather than being glazed. We carry the Delta Ceramcoat acrylic paints and use them to paint some items that we sell. For example, we paint some of our large Christmas trees with acrylic paints.
The slip that we use in slip casting our own pieces has been tested to ensure its compatibility with commercial glazes and in particular with the Gare glazes and underglazes. Several months were spent finding and testing the correct slip for our slip casting. Gare was kind enough to help us in this process by suggesting potential suppliers for the slip and in testing of bisque pieces through their testing processes. We are presently using the Miller slip from Laguna for slip casting since it had the closest characteristics in the bisque we fired to commercial bisque.
Gare Glazes on the Shelves to the Left, Extrusion area to the Right
Because earthenware can absorb water it should be covered completely with a glass forming glazes to make finished pieces. To accomplish this the pieces are held off of the shelves when being fired with their glazes so that the glazes do not touch the shelves and freeze the pieces to them when cooled. The small posts that hold them up are called stilts and they have high temperature wire points that actually touch the piece during firing. This allows the piece to get a complete coating of glaze and allows the stilts to be removed after firing since the high temperature wire does not adhere to the glass covering that is formed. Most commercial dinnerware is earthenware. You can usually tell earthenware by the stilt marks and the fact it has glaze on the bottom where it would touch the shelf if not stilted.
For stoneware we use a combination of commercial (Gare glazes are just used on earthenware) and formulated glazes. Formulated glazes are designed using both computer software and testing of samples by glaze firing. Stoneware glazes are where most people experiment with glazes. Testing must bring the glazes into the expansion rate where they will not shiver (pop off due to low expansion) or craze (form cracks due to high expansion) on the finished piece. They must also be prevented from having pinholes or other glaze defects. This type of endeavor is very hard to achieve without testing. Glaze software is also very useful in determining the expansion rates of the glazes, the fluxes present, and the silica content. Commercial glazes have to be tested with the various clays that are used. In some cases they will pinhole, craze, or shiver with one clay but not with another. A very interesting topic for exploration is high temperature crystalline glazes. For stoneware the effects which can be achieved with glazes are much broader than with earthenware glazes. However, the colors that can be achieved are less vibrant due to the higher firing temperatures which burn out some colors.
Stoneware cannot be stilted because the stilts would melt at the higher temperatures of the glaze firing. Also stoneware at this higher temperature approaches the melting point of the clay and stilting would allow the piece to distort around the stilting points. You can usually tell stoneware by the lack of glaze where it touches the shelf and by its hardness and inability to absorb water. It is more difficult to get vibrant colors at the temperatures of a stoneware glaze firing, although modern stoneware underglazes can approach the colors achievable with earthenware in some case. However, usually you see stoneware with more subdued colors in green, tan, yellows, and browns. Blues are an exception. They can be very vibrant with stoneware. This is why you see a lot of stoneware with blues in the decoration.
The studio has a Bailey Extruder System, a spray booth, a cink, and a North Star Slab Roller. It also has numerous small tools used in glazing and hand building such as scales for weighing, sieves for processing glazes, viscosity measuring tools, plaster bats, paint brushes, mixers, air brushes, banding wheels, slip trailing bottles, etc.
Extrusions (Bailey Extruder System) - This is a process where the clay is forced down through a metal or wood die that has a pattern in it. It forms clay into items such as round, hexagonal, or square tubes. It can form up to an eight inch round tube or an 8 inch square tube. It also is used to make ribbons of round clay, sometimes called coils, that are used in hand building coiled shapes such as pots.
Bailey Extruder and Extruder Dies and Parts on Shelf
Various Vases made from Extrusions
Slab Rolling (North Star Slab Roller) - this is a process where a lump of clay is sent between a set of rollers which flatten it into a slab. The thickness of the slab can be adjusted by adjustment of the slab roller wheels. Slabs are then used to make items such as tiles, bottoms for coiled pots, hand built pots, rectangular pots. sculptures, or other items.
Hand Building - there are numerous techniques for hand building. Generally it is considered to be different than wheel throwing. However, the two areas do overlap since wheel thrown pieces are often modified after throwing through some type of hand modification. The equipment used in hand building includes the extruder and slab roller but extends to most any tool that the individual thinks would be interesting to use with clay. The skills required are more along the lines of creative and design skills and less along the lines of muscle and hand pressure such as is used in wheel throwing.
Keeping clean (Creative Industries Cink) - the Cink is a self contained sink with water that is recycled through filters. Its purpose is to keep clay out of the normal waste system of the building. It is used to wash clay and smaller amounts of glazes from hands and equipment. It is important in a ceramic studio to wash up so that dust is kept down. Generally you use water or a vacuum to clean an area rather than a broom.
The Cink (washing up)
Spraying (Spray booth) - The spray booth is used for spraying glazes and acrylic paints. Using a spray gun or an air gun allows glazes to be put on more uniformly and allows special effects to be used in decorating a pot. Using the spray booth requires some instruction and the individual must wear a facemask when spraying.
Spray Booth to the Left, Stoneware and Earthenware to the Right