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Glazes and Glazing Techniques: A Glaze Journey, by Greg Daly

Potters use recipes that are passed from one to another and do not understand why the same recipes do not work for everyone. In this book the mystery and involved chemistry are replaced with a practical, straightforward approach to glazes and their application.

Chemical formulae are avoided as far as possible. There are many books which cover the chemistry of glazes in depth, with information on oxides and other materials, and do it well. This book is about a personal journey developing and discovering glazes. Author Daly shows how simple it can be to develop a glaze and a color. You need no previous experience - only a passion for exploration and discovery.

If you are looking for glaze recipes you can turn to Chapter 6. It will be like viewing a friend's travel video - seeing but not experiencing. If you are looking for a better understanding of glazes, color development and surface finishes, begin at Chapter 1. A glaze recipe from a book is only part of what creates the finished surface. You may now be searching for what you believe is an elusive recipe, but you already have the recipe; what you are really seeking is how to control the other factors that determine the final result - clay bodies, kilns, temperatures, kiln atmospheres and the way you apply your glaze material.

This book is about a journey of discovery and understanding so that the development of color and surface finishes becomes not mysterious at all. This book provides approaches and observation skills which will give an overall view of what happens to materials in glazes, how oxides give different colors with varying base glazes and how application methods can alter everything. The development of glazes and color should be fun.

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Review by Charles Moore of Sacramento, California

A prefatory note: Since Greg Daly is Australian, some of the chemicals that he uses to develop his glaze studies are more common in Australia than in the US. He gives the frit equivalencies for three frits: Australian Ferro Frits > American Ferro Frits—4064 > 3026 (lead bisilicate), 4110 > 3110, 4113 > 3124. We do not have US equivalents for several other Australian frits that he uses. If you are interested in a book that gives you a series of glazes, this is not it; it offers, instead, a way to make some very educated guesses about how glaze chemicals will react when mixed and fired. Daly uses only random glazes in his glaze tests; they are not necessarily “good recipes.”

In addition, if you want to follow Daly’s plan for glaze development, you need to be temperamentally suited to making numerous glaze tests (some of which will not yield anything useful) and to keeping meticulous records of your testing. Each test tile must be labeled, and a catalog of glaze tests, maintained.

Greg Daly uses the journey as a metaphor for exploration into the world of glaze. Though most books on developing new glazes tend to use the Seger Formula or glaze calculation, which requires some knowledge of glaze chemistry, Daly’s book depends very little on chemical analysis. Daly uses the potter’s own visual observations of the glaze tests. Though I am committed to glaze analysis (specifically the Insight glaze calculation program), I have to admit that much in this book impressed me.

In some ways, this book would be a very good starting point for someone interested in learning the mysteries of glazes and glazing. The first two chapters—“The Journey Begins” and “Preparing for the Journey”—deal in some very basic matters: what a glaze is made of, clay bodies, kiln types and fuels, recording tests, and parameters for glaze tests. One very interesting part of Chapter 1 involves a series of line blends of Silica with a base glaze with the Silica removed. The glaze: potash feldspar 40, Whiting 20, EPK 10. The base glaze also contains 10% Red Iron Oxide as a constant. Daly then schematizes the blend starting with zero Silica, then 10%, 20%, etc. up to 60%. The schema, on the upper half of page 10, allows for both reduction and oxidation results. On the facing page are photographs of the line blends; one can compare both reduction and oxidation results. Very much in the style of Ian Currie’s grid method, the results reveal that a glaze begins to form at about 30% Silica and increases in fluidity through the 60% test.

What can one learn from this kind of empirical approach? Certainly, one can begin to understand the value of Silica to a glaze formula and perhaps even what some likely proportions may work.

Chapter 3: “Voyage of Discovery” gets us underway. Daly’s method of analysis is consistently two-pronged: (1) it is a comparative, empirical method, (2) and it relies upon the principle of line blends. For those new to the concept, it is simple: in a simple line blend, the potter takes a formula or a grouping of glaze materials and varies only one ingredient in a measured plan. In the case of the Silica line blends (above), the amounts of only Silica were varied in a consistent way from the beginning to the end of the tests.

Daly says: “[A] way to develop a glaze is to line blend two materials together varying the quantities of the materials—a material with a glaze, or two glazes together. This is probably the most valuable system of finding out simply and quickly the reaction between two materials, material and glaze, [or] glaze and glaze” (p. 31).

Daly says, “This voyage of discovery will be to find workable, creative, interesting surfaces with just one material” (p. 27). By this Daly means that as he isolates the effect of one oxide (chemical), you begin to understand better how that material works in a glaze or glazes. Daly depends not only upon discussion about his tests, but also upon graphs and photos to illustrate his points. It is very difficult to successfully express his study in words alone.

Daly uses the term “random glazes.” He says, “The process of picking any 4 or 6 or 7 materials along with an arbitrary quantity can produce some very interesting results. I call them random glazes…. All the materials were written down on pieces of paper and drawn out of a bowl. The weights were chosen in the same way.” To make his point, he uses several base glazes, which he claims are “random” and tests them with varying amounts of Iron Oxide, Cobalt Carbonate, Nickel Oxide, and Rutile. The photographs on p. 33 give a number of interesting looking glazes, showing color, mottling, texture, etc.

After exploring a number of line-blend combinations, Daly moves to “triaxial blends.” He says, “Triaxial blends are another way of blending three materials…or three glazes together” (p. 42). I will try to show briefly how a three-glaze blend might work. Daly uses multiples of 25% (50%, 75%, 100%). Daly notes that these large increments can be later refined if they seem to provide useful combinations. If we have glazes A, B, and C, one of the first blends might be A at 75% + B at 25%. A next blend might be A at 75% and C at 25%. A still later blend might be A at 25%, B at 50%, C at 25%. Because he has started with three distinct glazes, the resultant blends offer quite a range of possible combinations.

Next, Daly moves to “Square or quadraxial blend” (pp. 44-49). A verbal discussion of how one combines four distinct glazes in numerous combinations would be entirely too wordy to keep track of. Let me ask you to trust me here. Daly provides a most workable set of combinations of four glazes.

Chapter 4: Choosing Alternative Destinations offers some really interesting information. Here Daly finds a way to show how the various fluxes in glazes influence color. “The flux is a major controller of color, but how varied is the color response from coloring oxides used with different fluxes” (p. 51)? What Daly does here is truly unusual because he chooses to use 100% of each single flux to test its influence on glaze color. In reality, most glazes use several different fluxing oxides.

If we follow Daly’s chart (pp. 51-53) to see the effects of Calcium Carbonate, Zinc Oxide, Barium Carbonate, and Magnesium Carbonate on Iron Oxide, we find that the colors with Calcium Carbonate vary from purplish-blue through pale tans and even deep red. This chart alone should provide invaluable information for potters who mix their own glazes and want to experiment with coloring oxides.

“Arriving at a Temperature” (Chapter 5) asks how you can formulate a glaze at a particular temperature (^6 for example). Instead of using glaze calculation, Daly takes “any stoneware glaze and a low temperature frit” and line-blends them together. “Fire this line blend to the temperature at which you want the glaze to mature. The resulting line blend will provide you with glossy, satin, and matt base glazes, with the best results seen if increments in the line blend are not greater than 5%” (p. 59). Here Daly lays out a schema for empirical testing.

Daly starts his process by melt-testing 12 “common frits” and glass cullet at 1976° F on a tile sloping at 75° from the horizontal. Unfortunately, of the various frits that Daly uses, two (Ferro 3124 and 3110) are the only frits available to us in the US.

Because Daly presents quite a number of line-blend tests for glaze formation at various temperatures followed by tests for color response from selected blends for melt, I will choose part of one set of tests to clarify Daly’s method. Using a glaze made up of Potash Feldspar 63%, Whiting 12%, Silica 10%, and EPK 5%, he first runs a test for melt at earthenware ^03, then at ^4 mid-range. In both sets of tests, he begins with 100% of the glaze and 0% of the frit. Then he increases the frit by 5% for each test and decreases the glaze itself by 5%. In the ^03 range, he finds that frit 4110 gives the best melt at 90% frit and only 10% glaze. In the ^4 range, he finds that frit 4110 gives the best melt at 70% frit and 30% glaze.

Having established which amount of Frit 4110 gives the best melt (depending on the gloss/matt surface you desire), the color tests are quite simple, but revealing.

I would note, however, that if a newly revised glaze contains from 70% to 90% frit, the glaze may have some real settling problems, since there is so little clay in the batch. In addition, Daly’s tests tell us nothing about the durability or stability of the new glaze. Nor does it adequately predict “glaze fit” to avoid crazing or shivering. This consideration is obviously important in functional pottery intended for food use (e.g., leaching of oxides, possible toxicity); but it is also important in pottery that must be water-tight (e.g., vases, pitchers) and also for pottery work that may be exposed to outdoor conditions (e.g., ultra-violet rays, repeated freezing and thawing).

One of Daly’s glaze recipes starts with 60% Barium Carbonate—certainly one of the most toxic mixes that I have ever seen. Raw Barium particles are toxic to breathe; once fired, Barium is very difficult to stabilize to prevent leaching. It would be most unwise to store food or even water in a vessel containing Barium. Finally, pots that are not impervious to water pose a danger for use in a microwave oven; such pots, by absorbing water, may get hot enough to burn flesh.

“Discovering Color” (Chapter 6) moves the line blend approach in more complicated and more interesting directions. Daly says on the issue of further color development, “Randomly picking the colorant amount out of a hat is one way….But planned color blends will give a larger number of results with relatively little weighting and mixing. This is a method of incorporating more than one [coloring] oxide into a base glaze to give broader and more diverse results” (p. 71).

For the sake of clarity and common sense, I must stop this discussion. Daly’s effort is far clearer when you can actually see his grids and his resultant color tiles. I would add that I was greatly impressed by the many distinctive color, texture, and gloss/matt combinations that Daly is able to achieve simply by blending coloring and opacifiing oxides.

Finally we are “Nearing Journey’s End” (Chapter 7). Here Daly takes us methods of glaze application: dipping, pouring, spraying, and painting. Though these are glazing methods commonly practiced, what Daly brings to glazing principles is notable in the success of his work.

Daly’s tests here look into the effect of glaze-over-glaze: using different glazes and different colorants in the glazes, Daly’s pattern follows: “matt over a glossy glaze, satin/glossy, glossy/matt, satin/matt, matt/satin” (92). Then follows the result of Daly’s method: he has brushed five glazes horizontally on a series of tiles and then has followed by brushing six glazes vertically, both oxidized and reduced firing. Daly suggests using a piece of paper with a small that will allow the potter to examine the results of a particular glaze combination while blocking out views of other combinations. The results showed a distinct difference between the oxidized and the reduced glaze combinations (pp. 94-95).

Daly’s glazing produces some truly beautiful glaze work using differing techniques and glaze combinations. He uses a variety of glazing methods on each dinner plate that he shows in this section—pouring, followed by painting, followed by partial pouring, incorporating wax resisting, etc. One of the most unusual of his methods is “finger painting.” After brushing on part of the plate, Daly then covers about half of the plate with a thick glaze that he applies in a swirling motion with his fingers. This swirled design is further mixed with more finger swirling. Then a rutile glaze is poured over the unglazed portion of the plate.

Since I am not able to convey the surprising beauty of the results of Daly’s glaze techniques in the section—“Examples of Glaze Application” (pp. 96-130), I would again invite you to study his methods and results for yourself. I believe that Daly’s multi-glaze application holds particular attraction to potters who use oxidation firing; he provides a way to develop more interesting glazed work simply by varying the method of application and glaze-on-glaze application.

In sum, how do I evaluate this interesting book? What can I take away that will make me a potter with more options in the matter of glazing? Daly has showed how using just three or four glazes, applied via differing methods, can produce a piece of exceptional beauty.

In spite of my--I think legitimate--concerns about the durability and safety of some of Daly’s glazes, he has rejuvenated my interest in the value of line blending as a means of enriching my glaze palette for color and texture. The way in which Daly creates line blends is most valuable; the color photos of the experiments are simply beautiful and most informative.

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