Understanding Water

An anecdotal story about how recipes travel

While living and working in Mesa, AZ, my wife developed a process for applying slip to bone dry clay to achieve a crackled surface that looks great on her work. The white slip recipe used at the Mesa Arts Center is a well loved and simple recipe from Jeff Oestrich. To achieve the ideal consistency for crackle, the slip was made at a specific gravity of ‘1.43’ with the addition of Darvan 7 to create a cream-like viscosity. 

When we relocated to Oakland, CA, the recipe my wife used successfully for years no longer worked. All of the ingredients were the same except for the water source, so we tested the recipe by adjusting the specific gravity and Darvan 7 ratios with no success. When the specific gravity was too low it would settle in the bucket, too high and it would flake off; too little Darvan 7 and it would be too thick, too much and it wouldn’t crackle. It wasn’t until we were testing some of the glaze recipes we also knew and trusted from Arizona that I realized they too were no good in our new location; all except for one glaze recipe that included “Epsom Salt”; that one recipe looked correct. It was an “ah-ha” moment for me! The water in Mesa, AZ comes from the Salt river, which yes is just a name, but the water there tastes funky and as it turns out, is full of soluble minerals. The same Oestrich slip recipe in Oakland required a specific gravity of ‘1.43’ with an addition of BOTH Darvan 7 and Epsom Salt to produce a crackle slip that would adhere to the bone dry clay surface, stay in suspension in the bucket, and of course crackle. 

We solved a mystery and the work resumed, for a while… until a few months ago, when we relocated again, this time to Ypsilanti, MI. My wife got set up to make work only to realize that her slip recipe, once again, was broken. Long story short, in Michigan her slip recipe needs a higher specific gravity, but neither Darvan nor Epsom salt to make the slip crackle.

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Why don't we include water?

For years now, I have been mystified as to why every glaze recipe I have ever seen published or in ceramic studios doesn't seem to list water as one of the ingredients. It would be like a cake recipe that omits flour, assuming everyone knows how to add it ‘to consistency’. As explained above, I understand that glaze recipes don’t always travel well, but we are missing a key ingredient, or rather a key understanding on how to make glaze. I wrote this article to shed some light on the power of water, and how you can make your glazes work optimally for you all the time. 

How to Measure Water in Glaze

To get started on identifying the ideal water amount for each glaze in your studio I recommend you start by looking at glazes as they come out of the kiln. When you get a great result out of a firing immediately go to that bucket of glaze and see how easily it mixes. Assuming the glaze hasn’t settled hard, take a specific gravity measurement and record that as your target specific gravity. Most studios use graduated cylinders, filling up to the 100ml line with glaze and weighing it. In this example, specific gravity = weight of glaze / weight of water (100g). Now that you have a target specific gravity, next time you go to make a batch of glaze, start with 70% water in your bucket (ie: For every 1000g of dry materials, start with 700g H2O). I will then add my dry ingredients into the water. At 70% you are unlikely to have too much water, but enough to make a wet slurry. Once all of the dry ingredients have been added and mixed, add water in 5% increments until it is thin enough to run through a sieve. Check the specific gravity against your target. As you add more water the specific gravity will drop. Continue to add water in 5% increments until you reach your target and then record the results. Let the glaze sit overnight to give the dry materials time to wet. When you come in the next day, look for signs of settling as you stir it up. Apply glaze and fire a test tile to verify your result. If your test tile comes back looking good, then rock and roll, but if there is an anomaly, there are a couple variables to consider: Did you use the same application method on your test tile as the piece that came out of the kiln prior? Did the kiln in either scenario under or over fire, or reduce/oxidize differently?
    Best of luck clay nerds! If you have questions about anything explained in this article send me a message.

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