Ms. Salonga’s Ceramics – underglaze/overglaze workshop

Introduction: VATN met in October to create pinch pot animal containers in Ms. Salonga’s ceramics class. The follow-up meeting in December gave the VATN members the opportunity to glaze their creations. The following lesson is an introduction to underglaze vs. overglaze and how the two are a great combination in the classroom.

Underglaze vs. Overglaze

The glaze options are (a) underglaze or (b) overglaze and (c) combination of underglaze and overglaze.

a. Underglaze will fire matte. This type of glaze retains fine lines and details since it holds its structure during the firing process.
                 UndGlOnly
b. Overglaze will fire shiny. This type of glaze will melt in the firing process and as a result will not be able to retain fine lines between sections of different color glazes.  

OveGlPigs

c. Combination of underglaze with clear overglaze on top will retain the fine lines and details of the underglaze and will give a transparent shine. Please take note that clear overglaze must be used to see details done with underglaze. 

UndglPigs

UndOverPigs

Instructions

When the bisqueware piece is received and ready to be glazed the piece must first be rinsed in water. This is done to ensure no crawling occurs. Crawling is the result of a layer of dust between the piece and the glaze; when the piece is glaze fired the glaze will not properly adhere to the ceramic surface appearing like gaps or blotches of separated glaze. Some artists will use this effect on purpose, most of the time in the learning environment this is done by accident.

After the piece has been rinsed, the piece is ready to be glazed. The decision to use underglaze, overglaze or both will be made at this point. The glaze bottles, regardless if they are underglaze or overglaze, must be shaken up before use. Please take note that the bottles are tightly closed before shaking the glaze. There have been mishaps when students shake the bottles of glaze and have strewn across the floor since students have not closed the bottles properly when finished glazing. Palettes can be used for retrieving multiple colors or if enough bottles are provided students may take the whole bottle. 

A brush is used to glaze onto the ceramic piece. Before using the brush, the brush must be rinsed with water. Once again, crawling can occur from brushes since there is dust in the air and will settle onto dry brushes. 

All glazes, regardless of what kind, should be layered in a criss-cross pattern to ensure full coverage on the ceramic piece. Three to four layers are recommended, but please check the label of the glazes that are being used for the best results. Every layer must be dry before layering the next. If the layers are not dry before adding the next layer, the glaze will be pushed around and there will be gaps in the glaze and it will appear splotchy. To know if a layer is completely dry, typically underglazes will appear less saturated and overglazes will appear dusty or pastel-colored. 

An example of a criss-cross pattern would be…

1st layer – strokes across from left to right

wait for the layer to completely dry

2nd layer – strokes beginning from top down

wait for the layer to completely dry

3rd layer – strokes across from left to right

wait for the layer to completely dry

If the piece is a combination of underglaze and clear overglaze the same instructions apply. There will be three to four layers of underglaze and three to four layers of clear overglaze after the underglaze with all layers drying completely before going onto the next. Please note to carefully overglaze the piece once the underglaze has dried. If the underglaze is not dry or if the clear overglaze is roughly applied the underglaze can smear. 

Things to be aware of…

The bottom of the ceramic piece where it sits atop a surface should not be glazed. If a piece has glaze at the bottom it may get stuck to the kiln shelf. If there is some glaze at the bottom of a piece it is recommended to use a damp sponge to remove the glaze. It is best to try to avoid glazing the bottom in the first place and using extra caution by cleaning the bottom with a damp sponge. 

Glazes can be expensive and it should be emphasized to students that we cannot be wasteful. Glazes are also harmful to the environment so students should be asked to lessen the amount of glaze that goes down the sink drains. If possible students should return glazes to their correct bottles. 

CombUndOvrG
BisqueMermUnder&AcrylMerm

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