I tried to have a cycle of jobs on the kiln I wanted to galze at "glaze pot->glaze craft->collect clay" while having a system of stockpile links set up. One stockpile takes from the other magma kiln making items, and the next was several floors up where my farms were (for brewing). It sometimes works, but requires several free dwarves to tag each glazed pot for hauling before the glazer gets around to seeing the same one conveniently in his workshop again. All the while my 500+ slag bar pile keeps getting higher and higher.
Now, there were already two kinds of glaze, ash and tin. Were they also mutually exclusive? I have never tried to tin glaze stuff before, even if tin was my only metal copper is too cheap to obtain in goblinite and from caravans to waste like that. Even if I had iron/steel, alloying bronze and using THAT to decorate something was always preferable. Back on point, I was only using the "glaze" reaction (as opposed to the BANDS of glaze). I wasn't sure if a glaze band would allow a pot to hold liquid or not. I can try fooling around with it some more.
Edit: But items can be improved by varieties of hte same source. I can add circles of both cat AND dog bones to the same item, but I can't decorate it with two turkey bones. I can stud something 10 times with 10 different metals, but they'd all be studs. Can you copy the code for other decorations for glazing? It might wind up giving glazing quality levels, but that wouldn't be a huge problem. I mean, DYEING has quality levels. Maybe higher levels would be like painting a picture or putting designs on the item.
Btw, the "bands" of copper slag were called "bands of opal copper glaze cabochons" or some such. About 10+ on one pot... so it is treating the bands as gem decorations?