Amaco underglaze on Kentucky Mudworks Porcelain Crazing

[LadyLumpsClay]

One of my students made this cool jar using Kentucky Mudworks Koda mid-fire porcelain. She painted Amaco velvet under glazes on during the green ware stage. We slow bisque fired to 05. Glazed in Opulence clear and fired to cone 6. She had crazy pulling away of the under glaze from the clay body. Any ideas on how to fix? Should she seal the underglazes or do a double bisque? Thanks!

[Min]

The peeling underglaze is  caused by the application, either too thick an application or underglaze itself was applied when it is too thick. For solid coverage it's best to apply several thin (water down the underglaze, most need this right out the jar) coats rather than one or two thick coats. Each layer needs to be dry before the next layer is applied regardless of whether the underglaze is applied to greenware or bisque. I prefer to put the underglaze on nearly dry greenware then bisque then glaze.

Is the glaze crazing in addition to the underglaze issue?

Edited April 12, 2023 by Min
clarity

[LadyLumpsClay]

Thank you! The underglaze was the only issue, the glaze was doing fine. I’ll relay this info and let her know. 

[neilestrick]

What you've got there is crawling, not crazing. Crazing is when the glaze crackles. The problem is likely from the underglaze being applied to thickly as Min said.