C ERAMICS 101 FOR YOUR CLASSROOM 10 SAFETY PRACTICES FOR YOUR CLASSROOM. Contents. Working with ceramics. in your classroom,

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1 Contents 10 Safety Practices 1 Non-Toxic vs. Dinnerware safe Are All Clay Bodies Created Equal? How To Choose The Right Clay For My Classroom How To Recycle Clay 3 The Firing Process 4 Underglaze vs. Glaze 5 Fired Defects 6 Glossary of Terms Working with ceramics in your classroom can be an exciting and rewarding event. But for those who do not have the background knowledge or experience, it can be a stressful and scary task. The world of ceramics has changed greatly in just the past few years. The capabilities of different clays has increased immensely and the color options have become endless. Even for someone C ERAMICS 101 FOR YOUR CLASSROOM with a strong background in ceramics, it can be easy to feel overwhelmed with where to start. Chesapeake Ceramics is committed to helping you understand basic ceramic principles and offering product knowledge so you can make educated choices for you classroom practices. For specific product information, lesson plan ideas, Clay In The Classroom newsletters, and classroom support contact our Education Specialist, Allison Jachowski, at or x SAFETY PRACTICES FOR YOUR CLASSROOM When working with ceramics in your classroom, there are a few basic safety rules to follow. 1. Keep a clean workplace. 2. Thoroughly clean materials and tools after use. 3. Clean table tops, floors, and spills with a wet sponge or mop. DO NOT SWEEP dried clay or glaze. This creates excessive dust that can result in upper respiratory problems. 4. Do not eat or drink when working with ceramics products. 5. Keep brushes and brush handles out of your mouth when working with glazes. 6. Wash your hands with soap before and after handling the clay. The oils in your skin can affect the clay. 7. Fire kilns in a ventilated area. 8. Keep children away from kiln while firing. 9. Do not mix different clay bodies without thoroughly testing. 10. Read every glaze label for firing instructions. Glazes can vary greatly in use, application, and firing.

2 Page 2 N ON-TOXIC VS. DINNERWARE SAFE If a glaze is labeled nontoxic, it does not necessarily mean it is dinnerware safe. Each glaze label will distinguish whether or not that glaze is non-toxic and dinnerware safe. Non-Toxic: Contain no lead or other materials that may be harmful to the human body. Dinnerware Safe: The surface of the piece is completely sealed and has no surface issues after the final firing. Surface issues are unsealed or open areas such as cracks, blisters, pinholes, craters, crawling, shivering, ect., that can result in bacterial growth and leaching of toxic materials. See Firing and Glaze Defects for more information. Commonly Found Symbols Non-Toxic Conforms to ASTM D-4236 Regulations Dinnerware Safe When Fired Properly Conforms to ASTM D-4236 Regulations Cautions Required The word ceramic can be traced back to the Greek term keramos, meaning a potter or pottery. Keramos in turn is related to an older Sanskrit root meaning to burn. Thus the early Greeks used the term to mean burned earth when referring to products obtained through the action of fire upon earthy materials. A RE ALL CLAY BODIES CREATED EQUAL? NO! Clay can be divided into several categories determined by the characteristics and firing temperature to reach maturity. 3 Most Common Clay Bodies Earthenware is made up of large particles and contains iron and other mineral impurities that cause the clay to reach fired maturity at lower temperatures. Earthenware tends to be porous and does not have as much structural strength as stoneware clays. Earthenware clay bodies are great to use when working with children. They tend to be easy to work with and can be fired at lower temperatures than other clay bodies. Colors range from gray, white, buff, red, or brown. Stoneware is made up of large and small particles that result in a much stronger clay body than earthenware. Stoneware ranges in firing maturity from mid-range (cone 5-7) to high-fire (cone 8-10). These clays are versatile in use and can be used for hand-building or wheel throwing. Colors range from red, brown, gray, white, and buff. Porcelain is made up of fine particles and is very pure in nature. The lack of impurities causes the clay body to be very white. Porcelain tends to be temperamental and can be difficult to work with at times. It can be found in mid-range (cone 5-7) and high-fire (cone 8-10). There are hundreds of clay bodies that can be found around the world. Most can be categorized as one of these three. BUT, not all earthenware clay is the same. This is true for stoneware and porcelain as well. Each of these three categories has many different sub-groups determined by the clay bodies firing temperature, color, and chemical make up. NO! Not all clay bodies are created equal!

3 Ceramics 101 Page 3 C HOOSING THE RIGHT CLAY BODY FOR Y OUR CLASSROOM When looking for a clay body to use in your classroom, you first need to ask yourself what cone or temperature you will be firing to. This will narrow down your search to one of the three most common clay bodies; earthenware, stoneware, or porcelain. Earthenware Clay Bodies Cone (1800 degrees-1930 degrees) Stoneware Clay Bodies Cone 5-6 ( 2120 degrees 2235 degrees) Porcelain Clay Bodies Cone 9-10 (2250 degrees 2350 degrees) Once you have narrowed it down to your desired firing temperature, you then need to decide what color clay body you would like within that category. When working with grades K-5, Chesapeake Ceramics recommends using an earthenware clay body. The low firing range is more suitable for the lower level students, perfect for K-5. Chesapeake Ceramics recommends using earthenware or stoneware for middle and high school ages. Stoneware is a stronger clay but needs to be fired to a higher temperature. R ECYCLING LEFT OVER OR DRIED CLAY How do I recycle scraps of clay after a project? Scraps can easily be used in the future simply by giving them a little TLC. Collect scraps in a large plastic bin for storage. Add a small water to the scraps and close the lid. Allow the clay to sit for a day or two to absorb the water. Take the clay out of the bin and wedge or knead the clay to create a homogeneous mixture. This will also rid the clay of any air pockets that may have formed. What do I do with a block of clay that is too hard to use? If the clay is too hard to use but is still moist enough to cut, cut it into small pieces and place in a plastic bin. Follow the same process you use when recycling scraps of clay. Depending on how dry the clay is, it may need to sit in the bin for a few days to absorb more water. How do I reclaim done dry clay? Place the bone dry clay into a plastic bin. Break the clay into pieces using a hammer or hard tool. (Wear a mask during this process to avoid inhaling clay dust). Pour water into the bin to barely cover the clay. Allow the clay to sit for a few days. Remove the moistened clay from the bin and place onto a porous surface such as canvas or wood. This will absorb the excess water. Once the clay is firm enough to handle, wedge or knead the clay to form a homogenous mixture and remove the air pockets. Place the newly recycled clay into an air tight plastic bag for storage. Can I recycle two different clays together? Chesapeake Ceramics does not recommend combining multiple clay bodies. Each clay body has its own formulation. When another clay body is added, it can alter the overall plasticity, firing, range, and glaze fit of the clays. This can cause cracking, not firing to maturity, glazes not adhering to the clay, and other possible structural and surface issues. The act of wedging clay will evenly disperse moisture throughout the clay. It will also remove any air pockets.

4 Page 4 T HE FIRING PROCESS Some of the first glazes were produced by the Ancient Egyptians using raw materials such as salt. Firing a Kiln Kilns fire according to heat work: time and temperature. We refer to this as cones. The number of a cone is a combination of temperature and time in the kiln. When using a manual kiln, a small cone is placed in the sitter. As the kiln fires, the cone will bend when it reaches the desired time and temperature. This will result in the kiln shutting off. Kiln Sitter Cross Section Digital Kiln Panel If using a digital kiln, use the Cone Fire feature to choose what cone you wish to fire to. The kiln is then programmed to fire to the desired time and temperature before shutting off. Plan to be present when the kiln is set to turn off. This is a safety precaution. Digital kilns can be programmed to fire on a delay in order to time them to shut off when you are present. Never open the kiln Pre-Firing Check List 1. Bottom of the kiln is raised above the ground on either a kiln stand or cinder blocks. 2. Kiln is properly vented with either a down draft vent (preferred) or a hood. 3. Kiln is a minimum of 18 inches from any combustible surface and wall. 4. Debris has been vacuumed from the inside of the kiln (should be vacuumed every firings or after a piece broke in the kiln and left debris behind). 5. Check for any rust or cracks in the thermocouple. 6. Pin back any sagging elements. Sitter with Cone Inside Kiln Sitter Box Outside Kiln if the temperature is above 150 degrees. Before firing your kiln, always run through a prefiring check list for safety. Loading the Kiln 1. Leave a 2 inch clearance around the thermocouple, between pieces, and lid. 2. Load the kiln uniformly, not heavy in the bottom and loose at the top (this will cause an uneven firing). 3. Stagger the shelves to allow for better air flow. 4. Load tall pieces in the center of the shelf and shorter pieces around the outside. This keeps the tall pieces from blocking the short pieces from receiving heat. 5. Be sure your kiln shelves have kiln wash on the top side only.

5 Ceramics 101 Page 5 T HE FIRING PROCESS CONTINUED Typical Firing Program on a Manual Kiln for Bisque or Low-Fire Glaze NOTE: Firing programs vary greatly depending on the type of pieces, how full the kiln is, and even the weather outside is a factor. If you are unsure of how slowly or quickly to fire your kiln please contact educators@chesapeakeceramics.com or x32 prior to firing your kiln. Keep in mind, this firing program will not work for all firings. This is only a suggested firing program that is commonly used. 1. Pre-Heat Bottom on Low for 3-4 hours. 2. All Switches on low for 2 hours. 3. All Switches on Medium for 2 hours. 4. All switches on High until the sitter bends to shut the kiln off (This time will vary depending on the desired final cone). 5. Bisque to cone 04, glaze fire to the cone on the label of the glaze. What is a Pre-Heat? When bisque firing, a preheat is ALWAYS necessary. Pre-heating is setting the kiln to a very low temperature for a few hours while the pieces are inside the kiln. This ensures that all the moisture from the clay is released before the firing process begins. It also prepares the clay for the increase in temperature and reduces the possibility of cracking during the firing. Guide Cone 3-Cone System Firing Cone Guard Cone Many products today, such as lead-free glazes, need to be fired within a 2-cone range. The 3-cone system can be used to determine temperature uniformity and to check the performance of the kiln sitter, electronic controller, and elements within the kiln. U NDERGLAZES VS. GLAZES The world of glazes and underglazes has grown immensely in the past few years. When choosing color for your ceramics, there are a few ways to narrow your search. 1. Choose a glaze or underglaze that is in the same firing range as your clay body. 2. Decide on an application. If you want to apply color to the clay in the greenware state (non-fired clay) then you need to choose from underglazes, NOT glazes. 3. Within that firing range, decide what kind of finish you want for the final piece; gloss, matte, textured, bright colors, earth tones, etc. Be sure to always read the label of the glazes you choose for application and firing instructions. Underglazes vs. Glazes Underglaze a color product used on greenware (non-fired clay) or bisque. They are many made up of clay and a colorant. Because they do not contain a large glass component like glaze, underglazes fire to a matte finish and do not seal the surface of the piece. Once fired, underglazes are meant to have a clear glaze placed over them and fired again. Underglazes tend to be used for painting like decorations and can vary in applications from watercolor effects to opaque colors. Glaze are a combination of a glass (frit), glass melter (flux), clay, and a colorant. When fired, the glass melts and then cools to create a hard sealed surface on the piece. Glaze is meant to be applied to bisque ware. DO NOT APPLY GLAZE TO GREENWARE. The 3-cone system consists of 3 consecutively numbered cones: Guide Cone One cone below desired final Firing Cone Final desired Guard Cone One cone higher than the desired final Example: Cone 06 Glaze Fire (In order left to right on kiln shelf) Guide Cone 07 Firing Cone 06 Guard Cone 05 By placing these three cones in your kiln on a bottom shelf, middle, and top will allow you to see how each section of your kiln is firing. For additional information about the 3-cone system, please contact Or x32.

6 Page 6 F IRED DEFECTS When working in ceramics, there are a great number of variables that can affect the final fired outcome. Below are a few common defects to watch for. Some defects can be avoided, some can be fixed, and some result in a clay or glaze change. Early pottery vessels were first used for storing liquids and grains. Name Appearance Possible Causes Craters Crawling Popped blisters in glaze after being fired Glaze pulls away from itself to expose the clay underneath. Under-fired bisque Firing too quickly Heavy glaze application Glaze is too thick Bisque was dusty Oils on the surface of the bisque How to Avoid Fire bisque slowly Do not rush or quickly cool glaze fire Apply glaze Apply the glaze Dust off bisque before glazing. Wash hands before handling bisque to remove oils. Possible Dremel or sand down edges of the craters and re-fire to Apply a small glaze to the naked area and re-fire to Crazing Spider web of thin crakes appear in the surface of the fired glaze. Glaze cooled too quickly in the kiln. Glaze contracts more than clay body. Heavy glaze application. Allow kiln to cool slowly and do not open lid above 150 degrees. Glaze does not fit the clay body; choose a different glaze. Avoid heavy glaze application. s Not Likely If using a food safe glaze, when cracks appear in the surface, the piece is not longer food safe. Fused Pieces are stuck together after being glaze fired. Pieces were loaded in the kiln so close they touched during the glaze firing Leave at least a fingers width of space around all pieces during the glaze firing. If pieces can be pulled apart, dremel area and add a small glaze. Re-fire to

7 Ceramics 101 Page 7 F IRED DEFECTS CONTINUED Name Appearance Possible Causes Glaze Bleed Glaze colors blend into each other. Heavy glaze application. Layered too many glazes. Didn t allow glaze to dry completely before firing. How to Avoid Apply the glaze. Only layer colors if by glaze. Allow glazed pieces to dry for a few hours before firing. Possible s Not Likely Glaze Starvation Glazed surface looks matte after being fired. Not enough glaze was applied to the surface before firing. Glaze was under fired. Apply the glaze. Be sure your kiln is firing to the desired cone in all sections. Apply an additional layer of glaze and refire to the Pin Holes Small holes in the surface of the glaze after being fired. Under-fired bisque Glaze is too thick Bisque fire slowly Apply the glaze Apply a small glaze over the affected areas and re-fire to In Japan, potters are held in high esteem. The best Shearing Shivering Piece breaks during the firing. (Usually a clean split) Glaze peels or flakes off the piece after being fired. Kiln fired too quickly Glaze does not contract as much as the clay. Under-fired bisque Oils on the surface of the clay before glaze was applied. Slow firing time down. Choose a different clay body. Bisque fire more slowly Wash your hands before handling bisque. s Not Likely s Not Likely This is usually a clay fit issue. Replacing the clay is the most effective solution for the future. are designated as Living National Treasures by the government.

8 G LOSSARY OF TERMS Classroom Support: X32 Orders: X23 Fax: chesapeakeceramics.com Website: chesapeakeceramics.com 4706 Benson Ave. Baltimore, MD Bisque Fired, un-glazed clay Clay Earth material that is plastic when wet and hardens when heated. Consisting mainly of alumina and silica, Al2O3 2SiO2 2H2O. Dry Footing Removing glaze from the foot or bottom of the piece before the glaze firing. This will keep the piece from fusing to the kiln shelf. Dry footing is only on stoneware or porcelain pieces that have been fired to vitrification and are completely non-porous or earthenware pieces not meant to be used for food. An unglazed foot on a porous clay body will absorb moisture. The absorbed moisture will cause the piece to craze. Earthenware- A porous, large-sized particle clay body. Fires in the low- fire range and is porous even after the final firing. Comes in a variety of colors; white, gray, brown, red. Fit- How the glaze fits around the clay. The glaze and clay body must have similar shrinkage rates in order to have a proper fit. Improper fit results in shivering or crazing. Glaze- a combination of glass, glass melter, clay, and color. When fired, the glass melts and then cools to create a hard sealed surface on the piece. Glaze is meant to be applied to bisque ware. DO NOT APPLY GLAZES TO GREENWARE. Greenware- Raw clay, before the bisque firing. Immature Bisque- Bisque that has not been fired to the right temperature to be able to release the proper gases, organic matter, and impurities in the clay. Kiln Furniture- The shelves, posts, and stilts used in loading a kiln. Plasticity- The level at which a wet clay body can be molded, altered, or shaped. Porcelain- A nonporous, fine particle clay body that fires in the mid-high fire ranges. Very pure and always a variation of a white. Pyrometric Cone- Triangular prisms made up of a ceramic material used to gage the firing time and temperature of a kiln. Available in selfsupporting and kiln sitter styles. Shelf Cone- Pyrometric cones used to show the highest cone (time and temperature) reached on a specific shelf in the kiln. This can be used to guide you in your firing process or to test to see if a section of the kiln is mis-firing. Sitter- A mechanical devise used to hold a small When the cone reaches the desired time and temperature, it bends and activates the shut-off switch. Stoneware- A multi-particle sized clay that fires in the mid-high range. Contains a high amount of grog for structural strength. Comes in a variety of colors; gray, buff, red, brown, white. Underglaze- Made up of clay and colorants. To be used on greenware or bisque ware. Once fired, underglazes are meant to have a clear glaze placed on top to seal them and create a gloss finish. Vitrification- In a fully matured clay body, the spaces between refractory particles are completely filled with glass, fusing the particles together and making the clay body impervious to water. Kiln Wash- A refractory material brushed onto the top surface only of kiln shelves. This creates a protective coating on the shelves and helps prevent glazes from sticking to the kiln shelf. Leach- Materials slowly being pulled out of the glazes after it has been fired. Leather Hard- Unfired clay that is firm enough to hold its shape, but still moist enough to cut or attach additional clay to.