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Glass Saggars or Glass Forms

Sagging wine bottles

Glass Saggar or Glass Form

Sagging wine bottle on the kiln shelving


The glass form or saggar has been specially designed to hold the weight of the glass. The saggar's wide base and sloping sides provide a stationary platform for the glass during the sagging process.

The glass form also has a number of vents (holes) around the sides to allow for proper heat ventilation. These vents are specially important during the heating and cooling cycles. Other smaller vents are placed inside the glass form. These vents allow the glass to sag into each corner or edge of the form. Without these vents the sagging glass could trap gases, thus, producing an uneven sag, distortions, and even large air bubbles.

After cutting the glass to its proper dimensions, it is wise to lightly sand the edges of the glass using a medium grade of emery cloth. Sanding the edges will help to eliminate any sharp edges and cuts to your fingers and hands. Always wear safety glasses while working with glass. Thoroughly clean both sides of the glass with an ammonia base glass cleaner, and then place the glass on a paper towel. From this point on, handle the glass as little as possible, and only by the edges. Otherwise, your finger prints could show up on the glass after firing.

Set your kiln setter with a Cone 016 or to 1450 degrees Fahrenheit if you are using a pyrometer. Close all the peepholes and prop the lid of the kiln open. This will allow all the gases to escape. Turn the bottom switches to high. When the temperature reaches 500 degrees, close the lid of the kiln, and turn the remaining switches to high. Monitor the kiln until you have reading of 1450 degrees, which is approximately Cone 016.

Remember, you are sagging glass -- not trying to melt glass into the shape of the saggar.

A fast average fire will give you the best results while a slow higher fire will begin to melt the glass before it is sagged.

At its final temperature, the edges of the glass will become slightly rounded. At this point, turn off the kiln immediately. Shortly, you can begin venting the kiln by opening the peep holes. After the kiln has lost its color, you can continue venting the kiln by propping lid open 3 to 4 inches.

For further information, and for prices on designing custom glass forms, contact Masterline.

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