When I started making these glazes in late December of this year I was using 20 megohm resistivity de-ionized water at a rate of ~65 to 70% of the solids weight. I was ball milling them, but found that not ball milling produced a glaze that was only a little stiffer, but still usable. I also noticed that it didn't seem to make a difference whether I used de-ionized water or tap water. I began using tap water exclusively with no apparent problem and did so for months.

The tap water in my studio, just like the water in my house and irrigation system (3 wells) comes from a well drilled in limestone. The calcium carbonate level in the well serving the house was 348 ppm (2 ppm below the state maximum) and will turn a shower white in <2 weeks. We have had an extremely dry late summer and fall and small ponds in the area have dried up, others have dropped up to 8 feet below their normal level.

Things started to change during late summer. I had to add more and more tap water to get the same fluidity in the same glaze and even then it didn't brush out as well as I remember. Eventually I was up to using it at a rate of 100% of the solids weight in order to get even a paintable consistency. It looked like my glaze was flocculated as I saw what I thought to be small flocs as it settled over time. These things didn't seem to be a problem until I noticed the glaze shrinking significantly on drying and peeling off the pots on drying and falling off in chunks during firing..

Was it possible my water was changing that much? How do I go about taking a look at the effect of my available water types on the character of my glaze, without going to too much trouble?

I decided to mix 100g batches of my 8% titania base (which seemed to be more problematic than others) with 70% water from various sources.

The first sample mixed was with tap water. It seemed much like the consistency that drove me to add more water in the first place. It was so thick it was difficult to get through the 80 mesh sieve and I listed it as "Very Stiff" in my notes.

The second sample was using a solution of 2 drops of Darvan 7 deflocculant per 1000ml of tap water. This result in an improvement in the glaze, at least by the standards of my crude eye.  I listed it as "Stiff".

I mixed the third sample using a solution of 10 drops of Darvan 7 deflocculant per 1000ml of tap water. This resulted in the "Stiffest" mix yet.

Finally I prepared the fourth batch using de-ionized water. This seemed to be the most fluid of the group and I listed it as "Loose - bubbles coming up".

There was a dramatic difference appearance of the stiffest and least stiff of the four preparations.

I used a series of home grown tests to characterize the rheology of these 4 glazes before sieving including:

     - A "Tap Test" where I smoothed the glaze in the container so it existed on one half of the container and counted the number of taps of the container on the table need to get the glaze to flow across the bottom and touch the opposite wall.

     - The "Ten Minute Angle" where I estimate the angle the glaze (which started at ~45 degrees) assumed after sitting for 10 minutes.

     - The "Vertical Tap" test where I counted the number of taps of my finger needed to get the glaze to flow vertically down and touch the opposite wall. Additionally I characterized the shape of the gob when it touched.

     -The "Fifteen Minute Shape" test where I observed the shape of the smoothed glaze in the container after it sat for 15 minutes.

And then, after sieving,  the "Time to Edge" test where I rotated the container holding the sieved glaze until the bottom was vertical and counted the seconds it took for the glaze to flow down and touch the opposite wall.

At the end of the testing there were noticeable visual differences in how the glazes appeared in their containers. The numerical results of the various tests described above are shown in my notebook.

The batch made using batch using de-ionized water was the most fluid of the entire group. The one made with 2 drops of Darvan 7 deflocculant per 1000ml of tap water was the next most fluid.

As the "proof is in the pudding" and this is all about glazing pots I combined batches 2 and 4 (with 1/2% cobalt carbonate and 2% manganese dioxide) then did a first coat on 2 bowls. After drying this layer appeared to be stuck tight to the piece. Then I combined batches 1 and 3 and did a second coat. There was a minor amount of peeling, but nothing like I saw before.

Things I will probably try in the future include using de-ionized water exclusively and possibly after further investigation a) reduce the water content to less than 70% of the batch, b) add additional CMC and c) add small amounts of Darvan 7 to de-ionized water.

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Phil Hamling

376 County Route 1

Warwick, NY, USA 10990