Galaxy Effect

[blue bronco.co]

Hi friends! Am a ceramics novice in general but especially when it comes to glazing. Quick question about why these mugs turned out the way they did…

The velvet under glazes bubbled and “clumped”(?) somewhat. Also, they remained with a matte finish/texture despite a glossy clear overcoat. It was only one coat of the gloss on top - should I have double-coated for all-around gloss?

Here is the clay/glaze breakdown:
Clay - Laguna B3 Brown
Base-coat - AMACO C-1 Obsidian (x 2 coats)
Colors - Coyote high fire underglazes (yellow-orange, lavender, sea grass, red-orange), most of which I applied in 2 coats

Any and all guidance is greatly appreciated! Be well.

[Min]

Looks like a couple things going on, the crusty look to the underglazes plus underglazes lifting off the base glaze.

If you find the underglazes too dry/crusty then another coat or two of glaze would be something to test. Some underglazes are quite refractory meaning they might still be dry even with an adequate glaze layer.

Lifting underglazes are usually caused by applying them too heavily or putting multiple coats on without letting the first coat dry first.

Looks like you put a lot of work into those mugs, going forward I would strongly suggest trying glaze/underglaze combinations on test tiles or small test pots before committing actual work to them. Typically underglazes are applied to greenware or bisque and not on top of or between glaze layers, like everything ceramics, test test test.

Welcome to the forum.

[Bill Kielb]

Very heavily applied underglazes can interfere with the overglazes ability to melt. Wash effects generally have greater success. Some colors are more reactive as well. Often the solution is to find an overglaze that works over heavy applications then test various colors and various brands of underglaze because some are more reactive than others. Even though that looks over fired, it can simply be underfired overglaze to which an overglaze that melts sooner will cover. We formulated overglazes that melt a bit sooner and have a bit more boron in them to melt more around cone 4 and this solved most of the issues for us. Spent one summer testing.

Anyway, lighter underglaze application, a different brand underglaze and then various overglazes tested are probably the best answer and as always, testing each color, IMO.

The first picture below is about our limit of performance for the overglaze. Very solidly painted but the overglaze still works reasonably well. The second is a picture of things we expected near perfect success. Note the yellow dot is quite thick and added as paint brush splatter so the expectation was the overglaze needed to just work in those circumstances.

Finally heavily underglazed items are hard to glaze as the underglaze closes off the pores in the bisque. I usually need to spray evenly, let dry then spray remaining coats drying in between to get the proper thickness.

[blue bronco.co]

Thanks for the feedback thus far, team!