Mrs Geraldine Edwards

[Geraldine]

I need advice re a glazing and firing issue. Some of my mugs are coming out of the kiln rough on the rim. This doesn’t happen to all of them in the same batch. Can I reglaze and refire? And what is causing this to happen. Many thanks

[Pres]

Geraldine, Welcome to the forum. Could you go in and change the title to something about glaze firing issues and repair? This will make responses to your question easier, and allow search engines in the future to find your post along with others of the same problem.

best,

Pres

[Hulk]

Could be the glaze layer at the rim is thinner.
Could be the rims were worked more at finishing, hence sand and/or grog are more exposed.
Could be a combination of both?

Reglazing and refiring, hard to say; some have luck with that, some don't.

Any road, building up a slightly thicker layer of glaze at the rim might help.
Using glaze that doesn't move/sag much might also help.

I'm curious if the problem mugs are together in the kiln, perhaps a hotter area?
I've used a buff stoneware that weeps tiny droplets when fired hot. The droplets stick but can be scraped off bare clay (e.g. the foot ring). The droplets will be hidden in the glaze layer, where the glaze is thick enough, else there's a gritty feel.
It's annoying! ...haven't seen it in any other clay, just the one buff stoneware.

[neilestrick]

Mug rims need to be rounded, and you should never sponge the rim or it will get rough (if you're using stoneware). The sponge removes the fine particles in the clay and exposes the larger particles. If you do have to sponge it, go back over it with your finger and a tiny bit of water. Also make sure the lip has a good glaze layer. A thin rim is more comfortable to drink from, but too thin and it won't take glaze well, especially if you're dipping, because it can't take in enough water to leave a good deposit of glaze.Too thin a glaze layer and it'll feel rough.

[Rae Reich]

Compacting the rim with a scrap of clay-bag plastic is a trick I learned to give you a dense enough surface at the rim to absorb more glaze. Sometimes a clay is just so rough, with high shrinkage, that the bigger particles still poke out here and there. A judicious use of a bit of silicon carbide shelf, or other fine-grained grinding stone will take off burrs.