You won't be using any glaze because air-dried clay isn't baked. Avoiding glazing saves money but takes away the joy of things like colorburst glazes. Encourage your kids to explore with different ways to add color, just like they would with ordinary clay.
While adding glaze to a ceramic object is not required, it may improve the burned clay work on both an aesthetic and practical level. Many clay bodies are not vitreous until they are glazed. Most raw glazes do not resemble what they will look like when burned.... No. A porcelain object needs to be fired in a kiln at about 1,100 degrees F (566 degrees C) to make it durable while maintaining its attractive appearance.
Because water will evaporate from the clay during the burning process, you must ensure that it is as dry as possible before applying the glaze. Because leather-hard objects still have a high water content, some potters advocate allowing the clay to cure to a bone-dry level before glazing. This prevents cracking due to shrinkage.
Others fire their pieces fully cured, with just the final color applied. The key here is to apply the glaze while the piece is still flexible so that you can shape it as needed. If it's too hard, you'll need to re-cure it before painting.
Clay pots are available in both glazed and unglazed varieties. The glaze seals the clay's porous surface. A glazed pot will absorb heat more uniformly, will be easier to clean, and will not require "seasoning." An unglazed pot will look nicer and feel warmer to the touch. Clay pots make good containers for plants that do not like wet soil or high temperatures.
The choice between glazed and unglazed pots depends on how you plan to use them. If you want to keep the contents of your pot dry, then an unglazed one will be better because it will not leak. This is important if the plant you're keeping inside it is sensitive to moisture. Glazed pots can also be useful if you want to protect the plant's roots from drying out while it sleeps in the winter by covering it with soil or snow. Of course, these are just examples; sometimes you may want to use a moistened cloth instead!
Unfortunatelly, clay pots deteriorate over time and need to be replaced once they start to break down. This could be many years after you bought them. So while they are durable, they are not indestructible!
Glazed pots should only be used outside. They are made of glass and so can break if put in the trunk of a car or dropped on a hard floor.
Air dried clay is not suitable for cooking. As long as you use a food-friendly finish and work with ordinary clay, you and your students may make useful mugs, bowls, and plates that are safe to eat and drink from.
Because these firings require a lack of oxygen for the glazes to develop, they cannot be refired in an oxidation firing (electric kiln) or the reduction will be reversed. When re-fired in an electric kiln, the black will burn away, revealing the clay color where it is exposed. In order to reuse pottery that has been glazed black, it must be thrown again and fired in an oxidizing atmosphere.
When pottery is glazed black, the fire's carbon dioxide reacts with the silica in the clay to form glass. Because this reaction requires oxygen, it can never occur completely. Some areas may turn black while others remain white because there is no way to seal the surface completely. If you should happen upon some blackened ware, it was probably made that way intentionally - perhaps as part of its design - rather than by accident. Although blackened pottery cannot be repaired, it can be restored to its original color by throwing it again and using different colors for new glazes.
Black pottery is useful for decorating other objects or painting designs on the surface. Since there is no way to see what color the blackness is underneath another layer of black paint, it is best not to use colors that are too close to each other when doing so. Also, be careful not to burn yourself when handling black pottery!
It is possible to refire black pottery in an oven but only at very low temperatures.