Paint-your-own pottery studios have revolutionized the glazing and firing process of ceramic bisque.  Contemporary studios do such a large volume that it wouldn't be practical to hand brush glaze onto every piece.  It would take forever!  The ceramic industry had to find a more efficient way to glaze large amounts of pieces.  So, the dipping glaze was born. 

Once the painted pieces have dried for 24 hours they are ready to be glazed.  Even though the paints are non toxic, the finished pieces wouldn't be food safe without a clear glaze on top of them. 

There are two different types of clear glazes that the contemporary ceramic studios use.  Food safe glazes contain some lead and are toxic in the liquid and dry state prior to firing.  Once they are fired they are considered to be food safe as long as they are fired to the correct temperature.  For glaze to be considered food safe, it must be fired to a cone 06 which is equivalent to approximately 1830 degrees Fahrenheit.  

A few years ago a clear glaze was developed  that is non toxic in the liquid state as well as the dry state prior to firing.  This is a major breakthrough  especially for the contemporary studios.  With the large volume of pieces that they glaze and fire on a daily basis it is a much healthier glaze to use.   The American Society for Testing and Materials (ASTM) establishes the standards for health labeling. Any glaze that has a non toxic label on it has been tested by a certified toxicologist and is said to have no health risks providing it is used correctly. 

The glazing process itself is relatively simple but a few basic rules should be followed to insure success.   First the glaze must be mixed thoroughly.   Next the glaze must be tested for proper thickness.  A viscosity cup  is used to do this test.  You dip the cup into the glaze bucket.  As you lift the bottom of the cup out of the tank, begin timing the steady stream of glaze pouring through the hole in the bottom of the cup.  Stop timing when the steady stream begins to break.  In general a time of 25-30 seconds is considered acceptable.  Refer to the instructions that come with the viscosity cup to adjust glaze that is too thick or too thin.  Next, rapidly submerge 1/2 to 3/4 of the piece into the glaze bucket and quickly lift out.  Shake off excess glaze and  carefully set on a drying table.  Wait until the glazed portion is dry to the touch and glaze the remaining portion of the piece.  Overlap the glaze 1/8” to 1/4”  making certain that you didn’t miss any areas.  Use a brush to catch any drip marks and to touch up any missed areas being careful not to smear any paint in the process.  Let the ware dry completely before loading it into the kiln. 

Most of the kilns that are used by paint-your-own pottery studios are computerized and they can be programmed to the desired temperature and stored in the computer.  Cones are a numerical equivalent  used in the ceramic industry to identify temperatures that the kiln has to reach for different types of firings.  A glaze firing is done at a cone 06 or approximately 1830 degrees F.  Kilns are loaded from the bottom up and the kiln shelves are held in place by posts.  There can easily be 5 or 6 layers of shelves in a fully loaded kiln depending on the size.  In general taller pieces should be loaded on the bottom of the kiln.  Plates and larger platters do best in the center of the kiln.  All pieces must stand on stilts which are very sharp pins to prevent the pieces from sticking to the shelves.  No glazed pieces should touch  the shelves, the sides of the kiln, or each other or they will stick together.  The only time a piece can sit directly on the shelf is if there is no glaze on the bottom of it.  This is known as dry footing.  Be sure to leave enough room between the pieces, the kiln wall  and between shelves so there is enough circulation.  Use a medium firing speed  and allow the kiln to cool to the touch before unloading to avoid cracking. 

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