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Application Of Underglaze To Greenware And Bisque


ioensis

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I applied underglaze to a greenware pot and the piece has now been bisque fired.  I want to apply additional underglaze to the bisque for touch-up and for better coverage.  The additional underglaze dries lighter than the fired underglaze, and I'd like assurance that after the final firing the two applications of underglaze will appear consistent.  Your response will save me the time and expense of testing samples and/or of applying a uniform coat of underglaze to the complete bisqued pot.  As the attachment shows, a complete additional application would be very tedious.  Does your answer change if a clear glaze is applied before the final firing?  Thank you for your help.

 

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Consistency in color may depend on application thickness.  Some underglaze colors are susceptible to thickness (think of the difference in how one brush stroke, two brush strokes, and three brush strokes compare on a test tile) -- not unlike some glazes show color variation due to thickness, runs, etc.  Some underglazes are more translucent than others which are more opaque.  Some show strokes/thickness; others do not.  Those differences may not be apparent just after a bisque firing.  You are more likely to see any variation after a glaze firing.  A clear (or other color) glaze over underglaze compresses the underglaze between the glaze and clay body.  If you have different thickness levels of underglaze, you might see that effect.  Like most things in pottery, there are few guarantees/certinties . . . mostly you learn through trial and error with a particular technique or material. 

 

You can get a good idea of the glaze fired color of your underglazes by dampening the bisque fired underglaze with water.  Actual color after glaze firing will be affected by the clear glaze; some clears, if applied too thick, may obscure/cloud the color response. 

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I agree with the answer above ... So make your corrections in a way that it feathers into the pattern rather than making just a dab of color which could show up as a darker mark. Your original pattern was probably not perfectly applied to an even thickness so you can tell somewhat by looking closely to see if you can tell where it is thicker or thinner right now.

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Thank you, Chris and Moderator, but let me ask the question another way:

With everything else being equal, will an underglaze applied to greenware and submitted to both bisque and glaze firings appear the same as underglaze applied to bisque item and submitted only to glaze firing?

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I agree ... I have run tests on both types of application and I cannot see a difference. The choice comes down to production factors more than application choices in my opinion.

To clarify what I mean by production factors ... You can correct mistakes easily on bisqued pieces but trying to get rid of colors on green ware costs you any carved/ print detail you might have. Using underglaze on greenware might mean you can skip a second firing. Etc.

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