|Monthly Tech-Tip |
How to apply inside and outside glazes to a pottery mug and get them to meet at a clean line at the rim.
Key phrases linking here: liner glazing, liner glazed, liner-glazed - Learn more
This is a technique of glazing pottery (as opposed to the choice of a safe glaze for the insides of functional pieces). Different glaze colors on the inside and outside meet in a clean line at the rim. The technique is common in commercial ware and requires precision to execute well.
The process of applying a liner glaze to a piece (by pouring), applying wax emulsion and terminating it at the rim, then immersing the outside of the piece into a dipping glaze to apply another color to the outside.
This technique enables the use of a liner glaze, in this case GA6-B. These are most valuable where the outer glaze is reactive (melt-mobile, crystallizing or heavily pigmented) and therefore potentially leachable. Not only are liner glazes less likely to leach but they are less likely to craze, this assures water tightness and eliminates any potential for bacteria growth in the cracks (especially if the body has porosity). Liner glazes are also less likely to stain and cutlery mark, adding to the durability of pieces. The straightness of the dividing line is affected by the degree to which the two glazes bleed into each other. Liner glazing also adds a decorative element to pieces. This technique is also practical where mug walls are thin and cannot absorb enough water to dry the glaze quickly after dipping or brushing.
Notice they have a liner glaze. The outside decoration has been done using wax resist and transfer techniques.
The white inner liner glaze (that wraps over the rim) was not removed after the wax was applied. The outer glaze thus overlays patches of it near the rim. The meeting line has been blurred and the other glaze has run downward and crawled somewhat revealing patches of the inner one.
With the proper technique of applying a liner glaze you can make the outside and inside ones meet in a straight line at the rim rather than just have one spill over the other.
The outer green glaze on these cone 6 porcelain mugs has a high melt fluidity. The liner glaze on the lower one, G2926B, is high gloss but not highly melt fluid. Notice that it forms a fairly crisp boundary with the outer glaze at the lip of the mug. The upper liner is G3806C, a fluid melt high gloss clear. The outer and inner glazes bleed together completely forming a very fuzzy boundary.
Liner-glazing is a very good way to assure that your ware has a durable and leach resistant surface. It also signals customers that you care about this.
|By Tony Hansen|
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