Glaze blistering on outside of pot

[ShanRums]

Hello! 

I wonder if anyone is able to help me. I can't seem to get consistent results with this glaze I have bought (Terracolor Iberia). It comes as a powder and I mix it up and dip my pots in using tongs.

The insides of the pots usually come out how I want them (a sort of dappled brown, please see pictures in the link) https://imgur.com/a/JroEs8U . But the outsides get these sharp blisters, and sometimes also look like the glaze has applied too thinly (it goes a dull solid brown colour). I'm thinking the insides of the pots are getting a thicker coat, as it takes me an extra second to pour out the glaze. But from what I've read, blisters are more likely to occur when the glaze is thicker? So I'm not sure how that makes sense. When I did test tiles they came out perfect, so I'm v confused about where these blisters are coming from.

I fire to 1220C (170C/hr to 1120C, then 60C/hr to 1220C) and hold for 5 minutes. 

I could try pouring the glaze into the pot, letting it dry, and then dipping the outsides, but I'm unsure how I would avoid leaving gaps where my fingers hold the pot. 

Thank you for any help! 

Shannon

[Bill Kielb]

A few things strike me: It looks fairly thick in the pictures, were your test tiles applied the same thickness? This glaze appears matte, is it sold as such? What cone is the glaze and clay and did you use witness cones in any of the firings. BTW the five minute hold at the end will drive this toward the next cone higher so not sure why it is there or if it’s something you have proven works for you.

Edited November 11, 2022 by Bill Kielb

[neilestrick]

Is it as glossy as it should be? Looks underfired to me, which could account for the bubbles if it's reaching the bubbling stage of melting but not going hot enough for them to smooth out.