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^6 glazes and flocculation

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#1 yedrow


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Posted 09 April 2012 - 01:43 AM

I'm slowly working my way into ^6 glazes. I'm having issues getting them to lay down. I get the colors and the depth out of them, but they often take over 15 minutes to dry enough to be handled.

I've added muriatic acid to flocculate the glazes but it isn't having much effect. I've so 'flocculated' one of Roy and Hesselberth's glazes that it will now sit overnight without water puddling on it (the test batch sat for days). My guess is that it has become extremely thrixatropic since the volume holds its shape until shaken, then it becomes fluid.

There is either something that I'm just not geting about flocculating glazes, or ^6 glazes tend to by nature require what to me would be special handling. I'm used to using ^10 glazes that have undergone years and years of adjusting. Now, in my own shop, I'm experiencing a condition that doesn't react to changes the way the information I've found suggests it should.

Assuming that ^6 glazes don't naturally go on wet/fat/thick, is there something other than flocculation that will increase the flow of water through the slurry into the bisque?

I have my specific gravity at ~150.

#2 Marcia Selsor

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Posted 09 April 2012 - 06:02 AM

I have been firing with ^6 glazes for 31 years and never had the problems you describe. Could it be your clay or bisque temperature?
re you over flocculating the glazes?
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#3 clay lover

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Posted 09 April 2012 - 07:41 AM

Altho I know nothing about cone 10, I've been using cone 6 glazes for some years. Many from MC6 Glaze book. My guess is, either too thick in the bucket, or bisqued too tight for the glaze. I bisque to 05 and glazes dry withing seconds, unless over dipped at rims. I do find that the same slurry will dip on thicker on porcelain that stoneware from the same bisque load.
I wish I could comment on what spesific gravity these glazes are, but I'm not that technichal, sorry.

Having said that, yesterday I had a very frustrating glaze day, with a new strontium from Steven Hill's video used as a base glaze with other layers dipped over it. All these glazes dry immediatly alone but NOTHING will get the 2nd glaze to dry when put over the strontium based first glaze???? The strontium glaze feels greasy in the bucket, and the 2nd glas will sort of slide off and not dry, no matter how long it sits. It is not thick either in the bucket or on the piece, just WET. I finally used a heat gun to get the piece dry enough to handle, wonder what will come out of the kiln? You bet I used a cookie under that piece!

#4 yedrow


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Posted 09 April 2012 - 09:48 AM

I bisque at ^05 and I'm pretty sure the ware is good. I have a couple ^6 glazes that lay down right and two Zamek Floating glazes that lay down good. But I have a matte white (in name only) that is extremely fat (it has 2% bentonite in it though).

Considering Ron Roy has worked with this glaze, I'm figuring the problem is me or my environment (alkali water, etc.), but what I've read from Pinnell about adjusting glazes doesn't seem to apply to these glazes.

#5 neilestrick


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Posted 10 April 2012 - 02:48 PM

Keeping glazes suspended, assuming it is a well formulated glaze to start, shouldn't take much more than 2 percent bentonite and 1/2% epsom salts. Glazes that are very low in clay content (under 8%) may need more. They should go on the same as cone 10 glazes as far as thickness and viscosity in the bucket.

Suspension and drying time on the pot are two different things. Some glazes take forever to dry. It's just the way they are. This is true for glazes that are high in certain feldpars (Custer, for example), or high in clay content (slip glazes, for example). Drying time will also be affected by the thickness of your pots. Very thin pots become saturated and take forever to dry. Thicker pots do not become saturated, and can therefore disperse the water in the walls of the pot, leaving the surface dry to the touch very quickly.

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#6 yedrow


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Posted 14 April 2012 - 07:18 PM


This is where some confusion is setting in for me. I've understood that suspension was a function the electromagnetic surface charge on the clay particles and the capacity of that charge to migrate to a point on the particle, creating a pole. This then allows the particles to arrange themselves like magnets around larger objects, and in so doing cover them. In my own mind I've concluded that there is a particle to particle ratio, clay/heavy molecules, as well as a clay mass/non-clay mass ratio. So, if there are enough clay particles and they are polar enough they will suspend the heavier molecules (or at least slow their downward motion). This is called suspension.

Then there is the movement of water through the particles into the bisque ware. This is facilitated by the thixotropic nature of a well flocculated glaze. The particles form something like cells that act as screens to allow the water to move parallel to the planes of the clay particles and easily into the bisque. But, if the slurry isn't properly flocculated the clay particles lay down and the movement of the water becomes perpendicular to the plane of the aggregate clay particles and they form a barrier.

In other words, the mechanism by which larger particles are held in suspension is also the mechanism that allows the rheology of the slurry to yield its water into the bisque ware.

Is this not the case?

Note: I've only been working with glazes about three of four months in any real way. So I'm perfectly open to being totally wrong. On top of that, most of what I know is from books, not experience. I'm an experienced thrower and have worked around glazes for seven years, but I've only just began the glaze thing.

Also, I'm concerned that I haven't paid enough attention to my bisque process. I'm firing next Monday and I'll sit with the kiln to be absolutely sure the right cone is hit. No trusting the kiln sitter and thermocouple this time.

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