Ron Ball wrote me the following:

Hi George.  I am going to be putting in a load of dipped/poured and sprayed glazes on some pots.  My recent venture in this area resulted in a number of pots with glazes running off onto the shelves and a lot of chipping and repairing of those shelves so I could use them again.

I have a copy of John Britts new book Cone 6 The Complete Guide---, and I had a chance to go over some of the firing schedules he has listed in the book.  I emailed John on his thoughts and he indicated that he has had some problems with Stephen Hills schedule.

You have done a lot of spraying and I am not sure what schedule you use.  I don't single fire our work.  I have been using a schedule that our guild was using and that is when I ran into the trouble with this mixture of sprayed and dipped/poured pots.

I am not sure if a fastfire/slow cool is the best approach do you have any comments.

Ron

Yes, some of the glazes are quite runny and putting them into general use in a group studio without adequate training would be a huge mistake. Strontium Crystal Magic is fairly stable when thin to medium. "Thin" means just barely concealing the clay body's surface texture after firing. "Medium" means a slight thickening, but no movement at the bottom edge of the glaze on a vertical surface after firing. 

The water color blue and green are very runny and more so on top of SCM. Try to keep on the upper part of pieces, or above glaze stopping contours like horizontal slip trails, sprigs, or incised decorations. Use very thinly to change the color of SCM, and a little thicker to move and pool.

Fake ash glazes want to run and rivulet. You defeat their purpose if you don't put them on thick enough for this trait to develop. Use them at the top 1/3 of pots liberally, and conservatively near the bottom.

Mixing, layering, and movement are the characteristics of these glazes that give them their drama. Control comes with experience and paying attention. I still have occasional runoffs, and pots where I didn't get adequate coverage near the foot.

A one hour hold at the top of the firing cycle will magnify errors of glazes being too thick. It will also start the growth of crystals, and allow mixing effects to come out that give these glaze combinations the look of reduction firing. The hold on the cooling cycle around 1700 deg F really shouldn't have much effect on running, as the glazes should be stiffening. The purpose here is again crystallization and color development particularly of iron.

Scraping kiln shelves is part of the learning process. If you never have to do this, you are not pushing your glaze education envelope.