| From the pages of Pottery Making Illustrated
In the Mix: Sedimental Journey by Jonathan Kaplan
 | | You can make a simple sink trap from a plastic tub and some schedule 40 rated PVC pipe available at home centers or building supply stores. |
|
Proper disposal of clay and glaze materials is important to any ceramic
studio. While recycling clays is very basic, recycling glaze materials
poses additional issues. These issues can be easily dealt with,
provided you have a method that’s flexible and some basic understanding
of glaze chemistry. The keys to successful glaze recycling are a desire
to recycle, some common sense and a consistent methodology.
Mystery Glaze
The most common solution for disposing of old
glazes and scraps is to create a mystery glaze. Any glaze you’re
thinking of discarding—discontinued glazes, leftovers from test
batches, residue from rinsing brushes and tools, etc.—can all be saved
in a five gallon bucket. Label the bucket “Mystery Glaze #1,” put a
date on it and don’t add any more scrap to it. Start a new bucket
labeled “Mystery Glaze #2.”
Next, you’ll need some test tiles
and small test bowls. Thoroughly mix the mystery glaze, sieve it a few
times then apply it to several test tiles and fire them. Make sure your
kiln shelves are washed or that you place the test tiles in a small
bisque bowl or cut a small piece of insulating firebrick to go under
the test tile. You’ll also want to apply some of the mystery glaze to
one of the small test bowls—there’s a good chance it will run, so
protect your shelves!
|
Test Results
The fired test tile or test bowl provides a great deal of information, and from this you can make some decisions. If your “Mystery Glaze #1” contains iron oxide, cobalt carbonate or copper carbonate, chances are the glaze will be on the darker side of the color spectrum.
As you’re combining glazes that contain a large number of differing ingredients, there’s a good chance that the new mystery glaze may be more fluid and run off the piece, or in the case of the inside of your test bowl, pool in the bottom. If this happens, there’s a simple way to fix the problem.
To render a glaze less fluid, begin by adding a small amount of EPK kaolin or a ball clay. Start with 250 grams for a 5-gallon bucket of glaze, then mix, sieve and test again. Make sure you keep records and that no one else in your studio starts to use this “Mystery Glaze #1” until you’re done with the testing.
Clay contains alumina as well as some silica. The alumina can help control the viscosity or fluidity of the glaze, and the added silica can help reduce any crazing. You’ll reach a point where further additions stabilize any issues with this scrap mixture and voila! You now have a mystery glaze that can be used on both the inside and the outside of your wares.
Mystery Additive
If you’d prefer not to mix and use a mystery glaze, you can opt to use the scrap to create a new glaze additive instead. Make a series of thick low platters with rims, or thick low-profile bowls and bisque fire them. Place your wet glaze scrap in these forms and let the water evaporate into the bisque. Plaster bats in the same form also work. You can place drying bowls outside in the sun to speed up the drying, but make sure that they are in a protected area to avoid any wind blown detritus. Once dry, you can use this dry material as a coloring mixture to add to a glaze. Test as an addition in various percentages with a clear or white base glaze.
Using scrap glaze as an additive increases your glaze palette. While it’s impossible to know the composition of this dry mixture, you can create interesting glazes even though you’ll have a finite supply.
Back to Earth
As our glaze materials come from the earth, and most do not pose a hazardous disposal issue, they can be recycled back to the earth. If you’re a gardener or have some land, the dry materials can certainly be added to the soil as a conditioner. While I’m not a soils expert or even a gardener, some soils are acidic or basic, and glaze materials can be added to change the soil pH. Note: If your glaze includes metallic oxides or barium carbonate (or if you are unsure what’s in the glaze) this is not a good solution. These materials are hazardous and should be disposed of properly.
To render the hazardous materials inert, you can take the bisque bowl full of the dry mixture and fire it to your normal glaze temperature. The resulting solid hunk of glass can then be more ecologically recycled into a landfill. It may also be possible to donate your scrap glaze to a community pottery studio or art center.
Trapped Again
Clay and glaze scraps cannot go down the drain, whether you have a septic system or are tied into the sewer system in your city or town. If you rinse out brushes or tools in the sink, you’ll need a sink trap to capture the residue. When the trap is full, properly dispose of the contents.
Bucket Brigade
Conner Burns of Natchez Pottery in Natchez, Mississippi provided me with a basic outline of the procedure in his studio. He starts with two 5-gallon buckets in the glaze area. One bucket is for glazes containing no colorants, such as whites and clears, and the other bucket is for glazes with coloring oxides. He tests both buckets and adjusts for fit. Once they’re workable, he takes a pint or so of the colored scrap and adds it to the colorant-free scrap and tests. Another technique is to run a volumetric line blend of the two glazes and see what happens. This provides a great deal of information and can often yield a very workable glaze that you can then mix in a larger quantity.
“Claze”
Another way of reusing glaze materials is to take a few cups of wet scrap glaze material and, if you mix your own clay, add it to the mix. Potter David Hendley of Farmhouse Pottery in Maydell, Texas adds glaze scrap to his clay and says that there is no appreciable difference in his clay body. He finds that adding scrap material in this way is a very effective way of reusing scrap glaze. He emphasizes that this works when mixing a dark stoneware body, but not when mixing a white or light body such as a white stoneware or porcelain body! Always test a small sample before using the clay.
Readers Suggestions
• If you’re a teacher, when you test and correct a new scrap glaze in your school studio, give it an inviting name. Your students will gravitate to it immediately. My last scrap glaze was (don’t laugh) “Moonbeams.” It’s gone now, but we could have used twice as much as we had.
• I rinse all glazing utensils and bowls in a large vinyl trash can, and periodically pour off the water when the glazes have settled. When there is very little water left, I pour the glaze remains into plastic grocery bags and allow them to dry out completely. Then, when the local garbage collector has a hazardous waste day, I take the dried up remains there.
• Recycle all light color glazes into one bucket, and dark color glazes into another. Usually the end result makes a good base glaze, and if you don’t like the color, just add a bit of your favorite coloring oxide.
• Since I only use cone 6 glazes that all fit the same clay body, I rinse glazing tools and sponges in a bucket. When the bucket is full, I mix it, sieve it, and test it. Then for the next few glaze firings, I do test tiles with the slop glaze and additions of things like rutile, zircopax, cobalt, copper and various combinations. These are mixed up by volume, so they can be duplicated when I find one I like. This is a really fun thing to do since you never know what beautiful (and unique) shades and textures you will come up with.
• If you work with low-fire glazes and don’t have any bisque vessels around, find or buy cheap terra cotta saucers, fill them with unwanted glazes and fire to cone 05. You can end up with some very cool results, If not, they’re now OK to throw out with your trash. I have hung some of the finished saucers on the exterior walls of my studio.
• I have a five gallon bucket that I fill halfway with clear water at the beginning of a glaze session. I use this water for brush cleaning, bucket rinsing, holding the glaze mixer between uses, pouring off settled water on glazes that are too thin, etc. A couple of days after the final glazing session I pour off the clear surface water (plants get watered) and pour the settled glaze material into a large bucket called “Dad’s Stew.” I have been doing this for almost 25 years now. At the moment it is a blue green gloss glaze when fired to cone 6-7, but obviously the glaze color has changed (evolved) over the years and even when it is a color that I absolutely love, it isn’t possible to repeat the experiment. Ah, serendipity.
Jonathan Kaplan is a frequent contributor to PMI. He has been actively involved in the ceramics field for 40 years. He lives in Denver, Colorado, where he curates Plinth Gallery. He can be contacted through www.jonathankaplanceramics.com. |
Subscribe Today
to get great content like this delivered right to your door!
|
|