About Ceramics
Arealles ceramics offers free web resources, mold care advice, kiln tips, and ceramic terminology! At Arealles we want our visitors to do more than just buy a ceramic from us! We'd like you to get to know us on a more personal level and build trust! What better way to build a business relationship, than to offer expertise on kiln loading, firing and cleaning greenware, and mold care for free!About Add-Ons
Ceramic Terminology
BISQUE or BISCUIT
Unglazed ware fired to a temperature sufficient to harden but not mature the body.
GREENWARE
Unfired clay articles.
KILN
A heating chamber for hardening and maturing clay and glaze.
DRY BRUSHING
An effect achieved by applying color very lightly with an almost dry brush.
GLAZE
A liquid suspension of finely ground minerals that is applied by brushing, pouring, or spraying on the surface of bisque-fired ceramic ware. After drying, the ware is fired to the temperature at which the glaze ingredients will melt together to form a glassy surface coating.
OVERGLAZE COLORS
Colors applied on top of a previously fired glaze are called overglaze colors. After application of the overglaze colors, the final firing requires a temperature only high enough to allow the flux to melt into the glaze and seal the color. This lower-temperature parameter allows use of more delicate hues and a wider range of colors.
UNDER GLAZE COLORS
Blues, browns, grays, gold-pinks, reduction reds and celadon hues are typical underglaze colors. As the term indicates, these colors are used under the glaze. Since they will eventually be fired at the same temperature as the glaze, the variety of colors available is less than for overglaze colors. Most of the delicate hues available in overglaze colors will burn out completely if fired at the high temperatures used for glazing. Underglaze colors are made up of: (a) a colorant, (b) a flux such as feldspar to allow the color to adhere to the body, and (c) a dilutent like silica, calcined kaolin or ground bisque ware - - - these last materials are chosen to either lighten the color or equalize shrinkage. Practice and experience are needed to obtain the optimum thickness of application for all colors so that the final glazed surface shows no change in gloss over the decoration. The advantages of using underglaze rather than overglaze colors include: more uniform coloring; less likely to produce running (than oxides mixed with water); and greater durability.
SLIP
Slip consists of extremely fine grained clay particles which are sorted out from the clay matrix by soaking in water. Slip is often applied to exterior and interior vessel surfaces as a method for strengthening the bonds between coils and also to create a smooth surface.
Kiln Talk
Often a greenware item is cast with multiple pieces. The pieces or parts added to an item are known as "Add-Ons", and should be poured at the same time as the main mold. When all the parts are released from the mold, begin to add the parts.
STEP 1
Place a vent hole for air in the main unit if the add-on piece is hollow. This prevents a blow-up in your kiln by letting the air out of the add-on.
STEP 2
Neatly remove any spare from both pieces with a trim knife.
STEP 3
Slightly wet both pieces with water, using a soft brush.
STEP 4
Add a thin layer of slip to both pieces at the point of attachments.
STEP 5
Secure the pieces and hold in place until the parts bind. This takes just a few seconds.
STEP 6
With a soft brush, smooth out any excess slip around the joint. Remove any slip drips as well. STEP 7
If the add-on is heavy, it may need supporting with a piece of foam rubber or shredded newspaper.
What Cone is Needed for Firing your Piece?
When firing ceramic ware in a kiln , a ceramist refers to a specific cone number, instead of a temperature. Since different ceramic colors require different firing conditions to mature properly, cones are available in a series of numbers to allow for these differences. The most commonly used cone numbers for firing ceramic pieces in kilns are:
Bisque:
For nonfired color products / 04
For Crackle toneaze / 06
For Nonfired color products with glazed areas / 04
For general-purpose ware / 04
For porcelain / 6-10
For stoneware / 6-10
Glaze:
Luster (Mother of Pearl) / 020
Metallic overglazes / 019-018
China paints* / 019
Decals* / 018
Hobby ceramics glazes / 06
Porcelain or stoneware glazes / 6-10
*Check manufacturer's label for recommended witness cone.
Be aware that the lower the cone number, the cooler the firing, and vice versa. Also, numbers prefaced by a zero (eg. cone 06) are cooler than normal stand alone numbers (eg. cone 6). Heat increases as the cone numbers increase as shown by the following diagram:
Cooler <--------------------------------> Hotter
019 - 018 - 017 - 06 - 05 - 04 - 0 - 2 - 5 - 10
* These are general guidelines, so always check the specific witness cone.
The Best Way to Load a Kiln
First the Furniture
Kiln shelves come in all shapes and sizes. For economy of space, it is best to choose shelves similar in shape and size to your kiln chamber. For instance, use a round or multi-sided shelf in a round or multi-sided kiln. Keep the size small enough so there is at least 1 inch of space between the shelf edge and the side of the kiln or the Kiln-Sitter. Also allow some room between the top of your ware and the lid of the kiln and leave space for witness cones amongst your ware.
Select posts in heights to accommodate the ware you are firing. Leave some room between the kiln shelves for air to flow, for heat transfer and for removal of fumes.
Half shelves are very useful to improve air movement in the kiln. Use two side by side with a 1/2" space between them and you don’t lose much stacking space.
Some kiln manufacturers recommend placing shelves directly on the floor of the kiln. Most suggest using 1" posts to put the bottom up from the cooler floor. This creates an insulating layer much like a storm door.
Setters and Stilts
Air movement in the kiln is clearly a big consideration - one of the most important when loading a kiln. Ceramics need to heat uniformly to prevent warping and stresses in the ware. Air needs to move around shelves and around individual pieces.
Plates and tiles benefit from the use of tile and plate setters or stackers. Shelfstyle setters allow air to move under the large flat objects so they heat more evenly. Avoid heating large flat objects directly on the cooler shelf. If you are firing decorated tiles or plates, vertical setters economize on space, and sets can be stacked to fit even more.
Glazed ware needs to be stilted or dry footed or the melting glaze will stick the ware to the kiln shelf, ruining both. Stilts also provide space for air to move around all sides of the ware. Porcelain and stoneware can not be stilted. The stilts embed into the ware during firing. Instead, use high fire kiln wash or silica sand on the shelf. Use prop to prevent sagging of porcelain.
Consider Heat Distribution
It is important to evaluate heat flow in your kiln and to make this a consideration in loading. Use pyrometric cones to determine the heating characteristics of your kiln so you know where the hot and cooler places are. Arrange your ware with different sized pieces on the same shelf to allow better heat flow.
Don't Overfill
Perhaps one of the most important factors in good fired results is enough air to mature the ware - to burn out organics in bisque and develop best colors in glazes. Shelf and ware placement and the use of setters and stilts can all help this, but here are a couple more tips:
- When stacking bisque, invert bowls and mugs opening to opening instead of nesting- this helps air move around all sides of a piece and prevents black rings and spots in the bottom of ware.
- Fire bisque lids and bottoms together. To get the best fit for lids, fire them on the piece they match. This will let the two pieces shrink together so you get a good tight fit. Fire all glaze pieces separately.
- Leave space between ware - don’t overfill. There is a temptation to cram as much as possible into the kiln to economize on firing costs. Ware fired too closely together creates firing problems. If you must overfill, fire very slowly and vent adequately.
- Mix thin and thick-walled pieces together throughout the load don’t concentrate them in one area where they are competing for air and heat.
- Use downdraft venting to move air through the kiln and to remove fumes created during firing.
Caring For Your Molds
2 Useful Mold Care Tips
- If a Brand New mold sticks together, Never pry or force it apart! Doing so may cause the mold keys to break off. Instead, proceed with your casting as usual and the mold should separate easily by the time the piece of greenware is ready to be removed. If this does not work, try gently tapping the mold's separation points with a rubber mallet.
- Always place mold parts together to dry, so as to prevent warping of the mold. Do not force dry in an oven, or place damp molds close to a kiln or any other direct heat source. Do not dry molds directly on the floor but on top of strips of woods. This allows for circulation of air. Molds can be sun-dried. It is extremely important that a damp mold dries evenly from all sides. Drying a mold too fast can cause it to powder, chip, or warp.
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