Author John Britt investigates the use of common household materials to create unique glazes.
Cat Litter, Antacid and other non-traditional glaze materials. (Alternative Glaze Materials for the Modern Potter)
To create glazes the traditional way you need some basic building blocks: clay, feldspar, silica, whiting, dolomite, talc, colorants, etc. The same is true when you are creating glazes from store bought products. A simple reading of the ingredients list will reveal that many of the products we use contain high quantities of clay, silica, feldspar, etc. The difficulty can be finding sources of pure materials because one product may contain several ingredients. But that is no different from the problem our ancestors face had when they dug materials from the ground. It simply requires a series of tests to determine what combinations will make suitable glazes.
First we must find sources of the basic building blocks of a glaze. Clay is available in many products, a major one being cat litter which, in America, is usually coarsely ground Missouri fire clay. This is a very consistent and inexpensive source of clay for your glazes and it comes in handy 20 pound bags. You could also select the clumping type of cat litter that contains bentonite. Bentonite is a type of clay that, when wet, swells up to 50 times its volume. This is added to cat litter so that after the cat has used the box the owner can easily identify the obvious swelling clumps that need to be removed. This type of cat litter is great to use in glazes because it helps keep the glazes well suspended. Clay is also present in many other products including make-up and “mud masks,” but using these products to make glazes can to be very expensive.
Feldspars are available in the hardware or paint store in the form of a sanding medium called “rottenstone” and “pumice stone.” Essentially these are very finely ground (325 mesh) iron bearing feldspars. The pumice stone can be used to make a wonderful green celadon glaze while the rottenstone, which has more iron, makes great temmokus and caramel colored kakis. A nice thing about the rottenstone is that it contains magnesium oxide, which produces wonderful satin surfaces. If you cannot find the ground pumice stone it is also available in a block form that is used to remove corns and calluses from the feet. This can be ground by hand to provide a coarser mesh feldspar.
Silica is a little difficult to find in its pure state in products sold for uses other than glazes. But it is used in many products such as, toothpaste, cleanser, desiccants (gel bags in electronic products) and insecticides. I used cleanser to supply silica because it also provided some sodium oxide. The silica is used as the “scrubber” and the soap provides the sodium oxide. Toothpaste also contains silica, which is listed on the label as “hydrated silica.” Silica is also available as diatomaceous earth, which is sold in garden stores as an insecticide. It is a rock, mined in coastal California, composed of the shells of dead microscopic organisms, called diatoms. When the one celled creatures die, their sharp silica shells remain. These sharp shells are useful as an insecticide because they scratch the exoskeleton of insects causing them to get infections and die. It is also used in abrasives, cement, roofing, paint and plastics.
Portland cement is a source of silica but also contains alumina and calcium oxides. It can be used in glazes but the difficulty is that it has a very short shelf life because it hardens very quickly. In the same aisle as cement are the cement stains or colorants. These are a great source of iron, manganese and other coloring oxides that we use in ceramics. Actually my favorite source of iron is a cement pigment made by Bayer, called synthetic red and yellow iron oxide. Synthetic iron is the strongest form of iron oxide available, because of its purity and extremely small particle size. In fact, I use it in many of my standard iron glazes.
Calcium carbonate has been used for centuries by humans for a variety of processes and products. Our ancestors used plant and wood ash as a source of calcium carbonate as well as sea shells and limestone. Today, one of the most well known uses of calcium carbonate is in antacids. Rolaids and other generic antacids are primarily calcium carbonate but some also contain magnesium carbonate. Calcium carbonate and magnesium carbonate together form dolomite. Calcium carbonate is also sold in hardware stores as window cleaner and as the powder used to make lines on football fields.
A short walk down the aisle of any drug store will provide a multitude of other possibilities for glaze materials. For example, Alka-seltzer is an excellent source of sodium bicarbonate, otherwise known as baking soda. In addition to sodium bicarbonate, Alka-seltzer “Gold” contains potassium bicarbonate or what is commonly referred to as “pearl ash”. Sodium bicarbonate is also used in manufacturing textiles and glass, neutralizing acids, purifying air, treating paper and in the production of fire extinguishers.
Magnesium carbonate is readily available from several products, the tastiest of which is Milk of Magnesia. Baby powder is another excellent source of magnesium oxide in the form of talc, which means that you also get silica and a wonderful fragrance. Baby powder is treated to resist water, so it is somewhat difficult to mix into a glaze batch. I used a bit of liquid soap to break the surface tension, thus allowing the powder to become wet. (Be sure to check the ingredient list of the “Baby Powder” as some now contain corn starch instead of talc.)
As I tested the materials, I found that the iron impurities in pumice stone and rottenstone were sufficient to produce a nice range of colors including light blue, green, yellow, caramel and browns from light to a rich dark brown. Iron has a great range of color response in glazes depending on firing atmosphere and other oxides present. For example, calcium has a bleaching effect on iron, and thus can turn an olive green celadon to a light green, and with sufficient reduction and some added silica, will produce a very nice blue celadon. I added Crest extra-whitening toothpaste to my green celadon and, in heavy reduction, got a nice light blue celadon (see glaze #11). In the presence of magnesium and calcium, small amounts of iron will produce a nice iron yellow. (See glaze #2, which is very similar to the $20,000 Heino Iron Yellow).
This experiment in glazing has provided me with both a beautiful glaze palate produced solely from locally available products and an expanded understanding of the uses of ceramic materials in everyday life. The following glaze recipes were achieved solely by a conducting multiple series of line blend tests. Several books that have helped me in this investigation include, Mimi Obstler’s “Out of the Earth, Into the Fire,” and David Richerson’s “The Magic of Ceramics.”
I do caution against using these glazes for functional pottery, as all the ingredients as well as the subsequent compounds formed during firing process are not known. Experimentation should be pursued only on non-functional pieces in well-ventilated outdoor kilns.
RECIPES – ALL GLAZES WERE FIRED IN MEDIUM TO HEAVY REDUCTION IN AN UPDRAFT ALPINE GAS KILN.
#1. SATIN GREEN Cone 10
Pumice stone – 50.0 g.
Alka-Seltzer (Gold) – 14 tablets
Talcum powder – 10 g.
#2. Iron Yellow Cone 10
Pumice stone – 50.0 g.
Rolaids – 14 tablets
Talcum powder – 10.0 g.
#3. CARMEL Cone 10
Pumice stone – 50.0 g.
Rottenstone – 50.0 g.
#4. TEMMOKU cone 10
Rottenstone – 50.0 g.
Pumice stone- 10.0 g
Alka-Seltzer (Gold) – 2 Tablets
Calgon – 5.0 g
Rolaids – 11 tablets
#5. FAKE ASH cone 10
Cat litter -50.0 g.
Portland White Cement-15.0 g.
Fake Ash Variations:
#6. For a slightly lighter color:
Add: Comet – 7.0 g.
#7. For a slightly softer surface:
Add: Milk of Magnesia-4 tsps.
#8. For a more milky glaze:
Add: Neutrogena sunscreen for sensitive skin -7.g
#9. AMBER cone 10
Rottenstone – 50.0 g.
Pumice stone – 30.0 g.
Portland White cement – 20.0 g.
#10. WOOD ASH cone 10
Rottenstone- 100.0 g
Diatomaceous earth – 10.0 g.
Wood ash- 30.0 g.
Milk of Magnesia- 2 tsps.
#11. Blue Celadon Cone 10
Pumice stone – 50 g.
Alka-Seltzer (Gold)- 2 tablets
Rolaids – 12 Tablets
Crest (Extra-whitening) – 20 g.