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I have been using a ball mill (cement mixer with a poly drum inside) to grind down system 96 into frit. It seems to work well but I seem to be getting some sort of residue in the frit that is causing a grey clouding and opacifying of the frit when it is fired. The ball milling is pretty aggressive and I was wondering if the residue could be coming from the alumina milling balls that I am using. Has anyone else had any problem similar to this?

You might try washing the frit. I grind for powder and sometimes I feel like there is something as too fine as well.

Jordan,
Thanks for the suggestion. I just finished washing the frit. It was my thought too that the alumina residue would be fine enough to be washed out with water using a fine mesh screen. I haven't done any firing tests but the frits do look cleaner and the waste water seemed to have a lot of grey scum in it (hopefully that was at least partially the alumina powder).

Yes, any grinding or machining process is going to give you swarf, a mixture of residue from the abraded alumina balls, poly container and fine glass particles. If you fire with it, it'll muddy up your colors and cloud transparent glasses.

It's the same thing that happens when you grind enamels or anything else--you need to wash the grind in clean, preferably distilled, until it stops clouding over.

Cynthia,
Thanks for the response. I washed it as well as I could without getting obsessive compulsive about it and it is currently drying out. As soon as I get back to the studio, I will run a test on it. A lot of grey matter came out in the wash water so I have some hope that it will fire a lot cleaner.

Thanks again,
Terry

I had never heard of this, and welcome the information. Will you please tell us how it turned out?

The finest particulate is small enough to suspend in the water and won't settle out(at least not right away). Glass or alumina, that stuff can be weird.

Well I just fired up a piece that I used the newly cleaned frit on. The cloudiness was reduced by at least half. I would rather not have any of this haze in the piece. I cleaned the frit well and evidently still couldn't get rid of the alumina contamination completely. Does anybody have any other ideas for "scrubbing" the alumina out of this frit. Next time I ball mill, I will use steel balls instead. I have had some success in cleaning the ferrous residue out of frit ground with steel.

I just had another thought. When I washed the frit, I washed it several times with water. Would washing it with some sort of surfactant before I rinse it help release the minuscule particles of alumina from the surface of the frit grains?

Maybe try Jet Dry the dishwasher wetting agent.
Report back please

I just washed the frit with a water based degreaser that I often use to get a good clean on sheet glass. It is something like "simple green". I rinsed it well. I will let you know if it helps. If it doesn't work I will try the Jet Dry.

Well I rewashed the frit and used a water based degreaser with multiple rinses. It is significantly better. The washed and dried frit sparkles in the light. I also think that one of the reasons the alumina residue stuck to the frit particles so stubbornly was probably due to a static charge. Evidently, when glass (the frit) is rubbed against polyethylene (the drum of the cement mixer I use as a ball mill) a static charge is built up in the glass. I think that this charged glass then grabs the fine particles of alumina in the drum.

would a wetting agent such as Jet dry help deal with the static charge during the milling process or would you just get a mess of foam?

I am not sure Kevin but I think it would be a messy foam and would probably inhibit the balls from doing their job.

I realize this thread is as old as sin. My theory is you are picking up pieces of your poly drum. I've tried grinding frit in many things - if there is ANY exposed rubber or plastic, even just the sliver of a gasket on a glass blender,etc., you are going to have that grey clouding. Crushing with steel is unfortunately about as good as it gets, at least a magnet can pick out the steel.

I think that it was the alumina contamination from the alumina balls. I switched over to steel balls and I don't seem to have the problem. By the way, I use a muriatic bath to solve out any iron residue from the steel and it seems to work much better than magnets. Thanks for the input.