SCM and the Companion Glazes Run

[George Lewter]

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.

[George Lewter]

Even if you are not using the Steven Hill glazes, when you are layering glazes, you are creating eutectic melting points, typically lower than the melting point of any of the individual glazes. Layering increases the tendency for running.

[Denise Rainville]

Hi Ron & George, 

Depending on the piece, instead of pouring/dipping I sponge/brush some of the glazes.  I find that it helps better control the thickness of each layer.  This technique works well with SMC as I it allows me to have thicker and thinner layers of the one glaze on my work.  

I use SH cone 6 schedule - however in the instructions I have there is no 'hold the temperature for 1 hr at the top of the firing' - it is all in raising the temperature very slowly in the last 100 degree of the cycle and cooling very slowly from 1700 to 1500 degree.

I attach a photo of 1 of 2 pieces - it has a thicker coat of both SMC & watercolour green than the second piece (attachment in a separate comment)

[Brian Dean]

Ron,

I agree with George that the slow cool down from 1700 F to 1500 F should not cause the running off the pot problem, I use an iron saturate glaze near the bottom of my pots to give it a warm toasty look without having to put much of the runny glazes near the bottom. Ash glazes and fake ash glazes that run by their nature producing rivulets should mostly, as George says, be located in top one third of the pot. You can have a very light application of these glazes in the middle third but don't overdo it, and very little on bottom third of the pot. Don't eliminate the slow cool down if you want micro crystals to form via the Strontium Chystal Magic glazes or other crystaline matt glazes. This slow cool down is intrumental in my own pots in creating interesting surfaces with good texture and visual depth. If you just fire pots to Cone 6 with a short soak at the top and turn off the kiln you will end up with much less visually interesting pots. That's mostly why historically Cone 6 electric has gotten a bad rap for producing less visually interesting pots than Cone 10 reduction or Cone  10 wood fired pots. The only Steven Hill related glazes I use are the Warm and Cool versions of Strontium Crystal Magic and the Hanna's Fake Ash glazes. Outside of that I've have spent years testing other glazes I have found using Steven Hill's techniques to create my own unique visual asthetics. FYI

[Denise Rainville]

Hi Ron & George, 

Depending on the piece, instead of pouring/dipping I sponge/brush some of the glazes.   This technique helps better control the thickness of each layer which allows me to have thicker and thinner layers of the one glaze on my work.  

I use SH cone 6 schedule - however in the instructions I have there is no 'hold the temperature for 1 hr at the top of the firing' - it is all in raising the temperature very slowly in the last 100 degree of the cycle and cooling very slowly from 1700 to 1500 degree.

2 photos with same glaze - second photo attach to next reply

Denise

[George Lewter]

Thank you, Denise. I was thinking of SH's older firing schedules from 3-4 years ago. He would rise to where cone 5 went down and hold for 1 hr, which would give cone 6 through heat work rather than temperature rise. I still do that quite often.

[Brian Dean]

Hi,

One more thing. I only spray my glazes using Steven Hill's spraying and layering techniques. You have much less control over application thickness if you dip or pour glazes on your pieces as thickness is proportional to the thickness and viscosity of the glaze and how long you leave it in the glaze bucket when you dip it. And it's very hard to control application thickness when pouring as well. Spraying give much more control over glaze application thickness.

I use Mini HVLP gravity sprayers with .1 mm oriface and a compressor with regulator that I set around 20 PSI.

FYI

[Denise Rainville]

I had never heard 1 hr hold at top temperature - however it is something to think about for movement - very interesting.

PS:  I find your comment about scrapping shelves a necessary pain?  I hope to prove you wrong one day!!

Here is the second photo with thinner coats of SMC & watercolour green.

Denise

[Chris Beloni]

In his workshops, Steven recommends using ceramic fiber paper or a clay cookie under work to limit amount of shelf grinding.

[Dawn Atkin]

I hate, hate, hate cleaning shelves, but I love runny glazes, so here is a tip I learned form an elementary teacher and have incorporated into my crystalline glaze world:  Roll some grogged clay (long beach or death valley - something that matches your clay color) as thin as possible - so thin that it is hard to manage.  Cut into shapes that fit below your pot and will catch drips/runs.  I call these "chips."  Because they are so thin, they don't need to be bisqued to use.  Just use them as greenware and re-use if they don't get dripped on.  If your glaze runs, it will stick your pot to the chip, but leave a pristine shelf.  The chip is such thin clay it is easy to break off 99% of it and then grind off the rest along with the glaze from bottom of the pot.  It is the almost free version of ceramic fiber paper.

note: I do use wax with alumina on the bottom of my pots to help the pot and chip move over one another at different shrinkage rates.

[Denise Rainville]

Thanks Dawn for the tip, I will certainly try this.  I purchase liquid wax, from a pottery supplier, that I dilute and apply with a sponge.  Could you tell me how much alumina should be mixed in the wax?

[Dawn Atkin]

I have a very precise formula:  I grab whatever scoop is handy and put some in a recycled cottage cheese container of diluted liquid wax.  (I brush, but I can't image brush vs spounge matters.)  Hmmmm, if I need to put real numbers to it, I would say a tablespoon of alumina to a cup of diluted liquid wax.

By the way, if you use underglazes or stains on the foot of your clay, the alumina can cause white stains.  Give it a test before using on your masterpiece. : )

[Charna Schwartz]

Hi Chris, I use the clay cookies under all my pots and I brush on a thin layer of kiln wash /water onto the cookie, which has helped if I have a glaze run. Sometimes the piece will pop off the cookie.. Practice practice practice has increased my % of successes.
Chris Beloni said:

In his workshops, Steven recommends using ceramic fiber paper or a clay cookie under work to limit amount of shelf grinding.