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I'm teach fusing at a local art studio and recently I pulled a load out of the kiln and discovered silver stain on the backs of several pieces. I found out why that occurred, the kiln was used by another fusing teacher who fired uncovered silver on the shelf. Now I have to contend with upset students. Is there a way to remove the stain or am I just out of luck?

Rhonda

From the fired pieces? You could conceivably grind the backs down far enough to escape the stain, but it will be a hassle. Or you could fuse another opaque piece of glass (or a thick layer of frit) that's non-reactive onto the back and hide it.

Obviously, mark the shelf so people know not to use that one for anything but metals. You might want to reserve a shelf for only your class.

A painted and fired piece I did at Pilchuck became silver stained on the back. The instructor, Albin Elskus, protected the painted side (the front) with contact paper (vinyl) and washed the silver stain off in an acid bath. It all came off leaving the glass surface perfect and did not damage the painting.

This is a very dangerous procedure and he was properly attired in protective clothing. Perhaps there is a studio near you that is appropriately equipped to use hydrofluoric acid that may do it for you. Jen

Huh. It that works hf etching cream like vari etch from his glass might work. R.

Roseanna it won't be a shiny surface that may firepolish unevenly.
generic HF screen etch has been known to eat the wiring inside the walls of glass printing studios.
Make another piece on another shelf or sandblast/grind and re-fire hot enough on a new shelf to fire polish out the blasting/grinding.
It is often quicker and cheaper to cut your losses and start over.

Buttercup wrote:A painted and fired piece I did at Pilchuck became silver stained on the back. The instructor, Albin Elskus, protected the painted side (the front) with contact paper (vinyl) and washed the silver stain off in an acid bath. It all came off leaving the glass surface perfect and did not damage the painting.

This is a very dangerous procedure and he was properly attired in protective clothing. Perhaps there is a studio near you that is appropriately equipped to use hydrofluoric acid that may do it for you. Jen

The health risks associated with hydrofluoric acid (death, permanent internal disfiguration, life-long pain), hardly seem worth the candle.

I certainly don't advise doing it. I'm just answering the question about how it could be done by a studio that is equipped to do it. I believe some studios still use the method with flashed glass. Jen

The vari etch frosted surface firepolishes nicely. I use a respirator and ventillation when I use it. The fumes will burn your throat and eyes if you are not careful. R.

sandblasting, like acid etching removes glass, and can be fire polished.

Hydrofluoric acid is on the danger list just below nuclear power. I was trained to use it by 2 different master craftsmen. I managed to master the process, and then quickly decided to never use it without an OSHA approved acid booth, the cost of which is outside my budget. Sand blasting or belt sanding will remove the glass which is what is necessary.

I guess Albin chose the acid bath over sandblasting because the temperature required to fire polish the piece may have fried the painting. I had days of work into it and Albin didn't even suggest abandoning it. I still have it. Jen

Buttercup wrote:I guess Albin chose the acid bath over sandblasting because the temperature required to fire polish the piece may have fried the painting. I had days of work into it and Albin didn't even suggest abandoning it. I still have it. Jen

Albin was one of the people who taught me how to do it. These days in the USA, I don't even know how you get HF, considering how hazardous it is to ship. Back in the 80's I just drove over to the chemical warehouse and bought a gallon. I'm pretty sure that is not possible today.

Fire polishing a sandblast works at fusing temperatures not the 1250 we used for glass stainers colors.