Recoloring a Classic: Trying New Colorants in a Classic Pottery Glaze Recipe Can Lead to Some Great Results Deanna Ranlett

It's hard not to love a good old classic glaze like a Shino or a Celadon. But sometimes you just need a change. Deanna Ranlett pushes experimentation with her students to make glaze mixing fun as well as educational.

In today's post, Deanna explains a recent experimentation on the classic glaze Falls Creek Shino. In addition to sharing how they conducted the experiment, Deanna shares the recipes and results. - Jennifer Poellot Harnetty, editor

In my glaze formulation classes students will often bring in glazes to explore, tinker with, and make their own. Of these recipes, the majority of what I see are the old standards most potters have used at one point. Besides already having the ingredients on hand, using an old favorite often allows a comfort level conducive to experimentation (I push experimentation to make glaze mixing fun) and if you get in a rut, adding a little fun to your palette can be a good way to get those creative ideas flowing.

Also, another benefit of these ‘tried and true’ recipes is that they have a broad fit range with commercially prepared clay bodies. The recipe I used for testing and experimenting, Falls Creek Shino, has many variations and discussions pertaining to it on the popular Clayart discussion group. Popularity on a chat site doesn’t mean you shouldn’t test, but it does mean that some common glaze faults aren’t present with a recipe that has such widespread recognition. For example, this shino fits every speckled body I’ve tried, as well as white stoneware and porcelain—I’ve yet to see any shivering in three years of testing with my students. I would encourage all potters to run acid leaching tests with lemon or vinegar, run a glaze in the dishwasher for multiple cycles, and test with freezing and thawing. This is an important step because every potter fires differently and uses glaze in different ways. If you’re ever concerned about colorants or glaze ingredients leaching, you can send your piece to a testing lab for extra security. For a small fee, leach tests are run, and you’re given a detailed report of the results.

An important first step when exploring a classic recipe is to determine if all the ingredients are still commercially available. For our tests, the traditional Falls Creek Shino recipe called for Albany Slip—which of course, is no longer available and most potters substitute Alberta Slip. Colorants are by far the easiest way to experiment with a glaze. In an average base glaze, adding color is the logical next step because colorants can completely change a recipe’s appearance. However, if you take a not-so-average base glaze, like the Falls Creek Shino, adding color is unpredictable given the dark base color of the glaze. We tested 2%, 5%, and 10% of stains and 1%, 2%, and 4% of oxides. We found the ‘sweet spot’ for adding stains to be 5% and 2% for oxides.

In the original recipe, carved lines and texture allow the glaze to pool and collect the pretty cream color leaving the darker brown where the glaze breaks. So, in adding colorants, we were unsure if the background color or the foreground color would change. What we found is that the opacifiers allow the added colorant to float leaving the darker brown color below almost unchanged. The best analogy I can think of is of a root beer float—but instead of using vanilla ice cream, imagine you’d used a flavored, colored ice cream! Our results were honestly amazing. The tests maintained the depth and richness of the original glaze as well but allowed for the development of vibrant, opaque colors on top. Also, as a pleasant surprise, the Alberta Slip makes for a glaze that brushes and dips beautifully with virtually no settling in the bucket.

So when in doubt, or when you need a little something new in your glaze repertoire, pick up a classic and add some color!

Firing Schedule

I normally fire this glaze using the following schedule. This schedule is adapted from http://www.masteringglazes.com/.

• 100°F/hr to 200°F (no hold unless I glazed that day then I will hold 1 hour to make sure the pots are dry inside).
• 350°F/hr. to 2000°F (no hold).
• 150°F/hr. to 2185°F (test to make sure this will be cone 6 for your kiln! This temperature may need to be adjusted) I use a 15 minute hold.
• 9999°F/hr. to 1900°F (no hold).
• 150°F/hr. to 1500°F (no hold).