ABOUT GLAZES AND GLAZING
Glazes are glass. The fired paints applied to ceramics are actually silica, alumina and flux which, when fired, create a glassy finish on the surface of ceramic items. This silica mix is suspended in a liquid with chemicals that create color. It is designed to melt at certain temperatures and flow, creating a glass-like surface. The color you see upon completion of the painting process (before firing) is a dye or coloring agent that fires out. The color you see after firing is caused/created by the application of heat to specific chemicals. This dye is placed in the paints as a guide so the artist can keep track of what they are doing.
Glazes are applied to fired bisque and should not be applied to greenware! Very important – DO NOT glaze greenware! Like all things, there are exceptions to every rule, but this should be left for specific finishing techniques and not discussed here.
There are different types of glazes and glaze finishes. The amount of sheen is determined by the amount of glass that is in the ‘paint’. The higher the amount of glass/silica content, the more translucent the appearance. Color, added to the mix also will determine the amount of translucency. The most transparent is the clear glaze, or glaze with no color chemicals added. Glazes range from transparent to semi-transparent to semi-opaque to opaque with opaque being NON-transparent.
Besides those glazes that are shiny, there are glazes that are more matte or satiny in appearance. These have less glass/silica content. Matte glazes don’t move during the firing process, whereas, shiny glazes do. That is because when glass melts, it flows. Therefore, the less glass in a glaze, the less it will melt and the less it will flow.
Not all glazes are compatible. Always read your labels. The fumes in the firing process can affect other items in the same load.
There are several ways to apply glazes to ceramic bisque. The most common is to use soft bristle brushes and paint it on in smooth flowing coats. Most glazes require 2 to 3 coats of application in order to obtain a smooth glass-like finish once fired. As to whether you apply one or two coats depends upon your specific method. If you have a heavy hand, you will only need two coats. If you tend to apply the glaze more sparingly, you will need three coats.
Two things you need to remember. Stiff bristled brushes do not work well to apply glazes as they tend to leave an uneven application and also wipe/rub away previous coats. Another thing to remember is to make sure your glazes are thoroughly dry between coats. If you don’t, the subsequent application will just move around the previous layer and create an uneven application.
It is recommended that each layer of application be in opposite directions. For example, if the first coat is applied with strokes going up and down (vertical), then the second coat should be applied with horizontal strokes, etc. This is to ensure a more even application. Glazes should be smoothed out and not allowed to drip, nor should there be a heavy build-up in the crevices of designs and embossed areas.
Another way to apply glazes is by dipping. The process to dip your items requires knowledge of how your glazes react to thinning. Clear glazes work best. When diluting colored glazes, your color can be affected.
Potters most usually dip or pour glaze on their pieces; however, they also most often mix their own glazes and the formula they use is usually geared to a thinner consistency. Commercial glazes, however, for the ceramist, are primarily designed to be brush applied. Therefore, if you are looking to thin down a glaze for dipping, you might want to do some testing to see how thin you can make the glaze without affecting its finished appearance. The primary reason you will need to thin a glaze is so that it will apply evenly and will not puddle too thick in the design recesses/crevices. Too thick of an application creates an unsightly appearance.
Dipping usually only needs one application. Using tongs, the piece is dipped into the thinned glaze and then lifted up. The piece is then put on a rack until it is dry. There are some commercially made dipping glazes that have a quick drying agent in them which are wonderful to use, but they come in limited color selection.
When applied correctly, the finished piece will have a smooth glassy finish. If you rub your hand across it, there should be no rough texture. If there is, the glaze most likely was not applied thick enough. This can usually be remedied by adding more glaze to the entire piece and re-firing.
Modern day glaze formulas (since 1995) are safe to use. In the USA, EPA requires that all paints no longer contain lead. Manufacturers scrambled to re-formulate all their paints and have come up with some remarkable replacements. Some are better, some got lost. Some of the older paints are still on the market, so be sure to read your labels on any that were manufactured prior to 1995. When using older glazes, take safety precautions and do a sample testing as colors may have become unstable over time.
Firing temperatures will affect color. Colors are created as a reaction to applying heat to the chemicals. READ those labels. They will tell you which firing range will create the true color. Firing too hot will change some radically. Firing too cool, the glaze will not mature.
Happy glazing!
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