u/Huge-Lifeguard-8510

I just took this piece out of my kiln and I’ve never seen this kind of texture before. It’s not pinholes or blisters, but is rough textured and vaguely matte but only on the inside of the bowl. I believe it is caused by the use of underglaze but can’t figure out why. The reason I think it is due to the underglaze is because I used white underglaze only on the inside but did not use the underglaze on the grater texture in the center and that part seems normal.

The clay body is KMW brown bear and the inside has Amaco white underglaze (3 coats), followed by Spectrum Sangria (2 brushed coats), Spectrum Running Hot Chowder dots sponged on, and then Iron Lustre (2 light brushed coats). The outside of the bowl came out fine (Mayco black Engobe, RHC, and Iron Lustre) with a few minor pinholes.

It was fired to a hot cone 5 with a 30min hold at the final ramp (1900’). This piece was located on the bottom shelf. I had cones on each shelf, and all indicate it fired evenly to a hot \^5 with the middle shelf firing a bit hotter.

Every other piece came out fine in the firing - although this was the only piece that was made of Brown Bear, the rest were a mix of White Bear and Roo.

Any ideas why white underglaze might have caused this kind of reaction? Due to clay body? Temperature? Interaction between clay body/underglaze/glaze?? I’m baffled.