Glazes for Glass

My great curiosity for understanding the initial source of reactions between clay and glass led me to conduct material study as part of a research course led by Dafna Kaffeman and Tal Frenkel Alroy, in which I examine the feasibility of applying glazes to the glass surface. My interest is in the mysterious and raw world of materials themselves, their chemical elements, their composition and the way they compound and form relationships with the materials around them, definite laws that control the essence of every substance and material, like the function of DNA in the cell, the genius of chemistry and the biology of our world. Everything has its own place; there is order and logic and they are realized through connections or compounds, but what happens when there is no match? How do things express themselves out of chaos? As we know from the world of biology, when cells suffer disruption, mutations ensue; therefore, what disruptions can I create while searching for a glaze coating for the glass to make it appear organic?

This study came to be inadvertently, while working in the hot workshop. While inflating and shaping the hot and liquid glass, it is critical to maintain proper temperatures and any deviation from them will lead to thermal shock, cracking and breaking. To maintain the correct temperature, we have the “Glory Hall”, a fire-spewing kiln that can reach a thousand degrees, and that, from time to time, during the design of the glass bubble, the works are placed inside it to keep the material warm. To protect the kilns, plain sea sand is sprinkled inside them – one of the basic components from which glass is made. The sand that burns in the kiln’s high heat also undergoes a change in its chemical structure and becomes glass-like but rougher and cruder – it is not transparent but opaque, granular, light blue and lacks plasticity. When I worked with the Glory Hall, the glass exploded and fell to the bottom; I quickly pulled the work out and at that moment a very intriguing appearance was created – the sand stuck to the glass like a coral reef, mesmerizing blue organic shapes with gentle movement were created and the rocky-coral look enchanted me. Plain sand, energy, time and the right encounter.

Thus, in nature and its elements, in their randomness and accuracy, in their simplicity and complexity, the most exciting events take place. In my research, I sought to trace these effects. My inspiration was the works of Per B. Sundberg, a Swedish clay and glass artist, and especially a collection of works in which he created amorphous bodies from clay and laid on them layers upon layers of glaze that create an appearance resembling natural organic elements. I took more inspiration from artists like Mieke Groot and Sally Resnick Rockriver, who chose to engage in the same theme of organic, mutable appearance, pushing the raw materials into extreme situations where the interesting reactions take place.

By “organic form” I mean an indefinite form that attracts the eye to a closer inspection or that scatters the gaze in every direction. It can be a rigid and sharp crystalline structure or perhaps a bubbly, cracked or fractured one. In any case, the result is created by the same unordered reactions and bonds that form between the molecules.

I want to connect the worlds of clay and glass through their common feature, the glaze, which after all is a thin layer of glass. Since the glaze and the glass are made of the same material, their connection seems trivial, but because the glaze is a thin layer and not a full lump of material, this connection requires overcoming major difficulties in several key aspects:

1. Preparation method – The glaze is originally designed to be formed by melting and chemical compounding of its raw materials over a body whose surface hardens and strengthens during preparation. Not only are the glass surfaces not likely to harden and strengthen, they also soften and slightly liquify during heating to the glaze melting temperature, which may prevent the glaze from covering the glass surface and instead fuse with it into one body.
2. Matching the glaze to the glass surface – There is a large difference between the glaze’s melting temperature and the glass melting temperature. Glazes usually melt at 1050-1280 0C and even higher, but the glass body is completely turned into liquid at 850 degrees. In order to bridge the temperature gaps, the glaze recipes must be manipulated by adding a high proportion of melting agents, whose job is to lower the melting point of the glaze mixture. As a shot in the dark, I chose to work at 800 degrees because this is the temperature at which glass starts to turn but is not completely melted and out of control. For me, this is the maximum value at which I can work with the glass. The 800-degree choice is restrictive, since it can be used primarily on glass surfaces in slumping and fusing techniques.
3. Aesthetics – Learning about the nature of the glaze, and the way the glaze layer, color and texture can be controlled.

The world of glaze is endless, and there is a great interest in the special visibility of the surface, which completes the work. As far as the glass world is concerned, color is relatively limited to what is produced in factories and not as much freedom and leeway is allowed as in ceramic glazes. By re-examining the feasibility of bringing these materials together, I may be able to expand the palette, color, texture and uniqueness of the surface.

The first step in the work is to find out if such a connection is possible and which raw material will form the basis for glazing, which both melts at low temperature and able to compound with the glass surface without stresses and cracks. Under the guidance of Elisheva Rabin (retired lecturer in the Department of Ceramics and Glass Design at Bezalel), I examined which of the main melting agents can melt at 800 degrees and does not crack or create stress between it and the glass.

In addition, there is the problem of the glaze’s adherence to glass. Unlike ceramic material, glass is not porous and it not absorbent, so I passed all the glasses through a sand grinder, thus creating a rough surface. I also used different mediums or wallpaper glue for gluing, and finally added peptone to the recipes, to help the glaze thicken and adhere to the glass.

After testing in the lab (Image 2) where I found out which melting agents bond well with the glass – mainly the frits (frit is an artificial blend of melting agents with silica, which is melted, cooled and ground to powder and used as raw material for melting glass in ceramic mixtures), I started looking for recipes for very low temperatures of about 800 degrees, such as the Raku firing, based on the 3110 frit melting agent, which produced the most promising results.

In order to understand in depth why the connection between 3110 frit and glass gave the most promising results, I checked the specification of the same compound. It has 70% silica, a bit of alumina and a lot of melting agents that lower the temperature to a relatively low value (melting range of 760-926 degrees). Therefore, it is clear why it is optimal for connecting the glaze to the glass, since most of it is silica (glass-forming material) and, with some more melting additive, could be lowered even to 800 degrees.

Image 2: Checking melting agents at 800 degrees

1. Borax – merged with the glass, completely translucent but formed many stresses and cracks.

2. Lithium carbonate – sticky, half melted, white crystalline appearance, interesting texture.

3. Alkaline 3110 frit – superb, no cracks at all, remained somewhat white and completely fused with the glass.

4. Enhanced calcium borate 3134 frit – really excellent, fused with the glass, matte-white color.

5. Calcium borate 3124 frit – not good, many cracks, white-yellowish color.

6. 6004 borax frit – fused with the glass, with some stress and one big crack formed, matte-white color.

I did a preliminary check for some random recipes I found, which rely mainly on the frits that were found to be the most suitable for use in high proportions. I first tested the recipes without changing them and then added cobalt and copper tones, since the frits are alkaline, and the literature says they reinforce blue tones.

I cannot use industrial dyes because they are fireproof and do not melt at 800 degrees.

The results that came out of the kiln were surprising and very exciting, as the three recipes fused with the glass without stresses. Of the three recipes, the first one gave the best results for what I was aiming for – an uneven, mutable, eye-catching, bubbly and untidy look that induces an organic feel. Since the world of glazes has countless possible compositions and combinations, I decided to stick to recipe # 1 and continue to test with it more colors and more textures that I can produce.

I also noticed that using cobalt, which is also considered a melting agent, encourages the bubbly and organic appearance I was looking for.

Image 3: lab testing three frit-based recipes

Recipe # 1:

3110 frit- 65g
Gerstley borate- 35g
Bentonite- 2g

Recipe # 2:

Gerstley borate- 40g
3110 frit- 40g
Nepheline Syenite- 20g
Kaolin- 8g

Recipe # 3:

Lead frit- 66g
Quartz- 30g
Kaolin- 4g

With the help of Elisheva Rabin, I continued my exploration – how could I promote the reactions and strengthen them? And so I tested the effects of silicon carbide, bone ash and magnesium, which are known to produce interesting glaze textures. Bone ash produces tiny, pink bubbles, silicon carbide creates a lot of neat, definite murky-gray bubbles, and in large quantities it turns black, and magnesium produces a kind of islands or parched earth. The test produced good results – bubbly and cracked as I wanted, but I realized that in order to achieve an extreme effect, I had to dare and use these materials in higher proportions, and I also realized that layering the glaze was very important: it was better to use a thick layer to produce the desired effect.

Image 4:
1. Magnesium; 2. Bone Ash; 3. Silicon Carbide

In order to expand the color palette, I used Rutile to produce a brownish-yellowish-earthy palette and enamel dyes, which, unlike industrial dyes, are designed for low heat firing, so they will be a perfect solution for stronger and more prominent tones. The glaze blend exhibits good flexibility and stability with regard to additions and changes in color and texture, so I continued to experiment in the lab with all those minerals and chemicals that I had not yet tested for color, and I used nickel, chrome and manganese. The biggest surprise was lithium, since in combination with the enamel dyes it completely removed the pigment and combined with the manganese created a silver patina, as if it were a reduction in the kiln.

Image 5:
1. Rutile; 2. Nickel; 3. Chrome; 4. Manganese; 5. Lithium and silvering; 6. Enamel Dyes

In an attempt to understand the interesting reaction between lithium and manganese, as part of the test, I tried to reconstruct and study volcanic glaze and see in what doses the reactions start and when the silvering begins. I divided the recipe into ten cups that were equal in their particle density, to which I added, in varying ratios, lithium and manganese.

Basic recipe: 3110 frit weighing 65 grams and Gerstley Borate weighing 35 grams. Separately, I weighed 2 grams of lithium and 2 grams of manganese and in each of the 10 cups I changed the amount: in cup number 1 (upper left corner) I added the most manganese and the least lithium, and the opposite in cup number 10 (the lower right corner).

Image 6: Testing lithium and manganese in varying ratios

Results: the glaze came out volcanic, as planned, but without silvering. After a conversation with Racheli Wakshlak, a chemist and technology lecturer, I realized that the manganese is responsible for the silvering, but it should be added in very high doses. The 2-gram amount does not yield the radical change and the violent reaction as seen in other tests. What can be learnt from this test is that the more manganese is added, the darker and denser the product becomes, and the more lithium is added, the lighter and airier the product becomes. moreover, lithium slightly corrodes the glass surface.

On further examination, I took the basic recipe with which I work (65 grams of 3110 frit and 35 grams of Gerstley Borate) and added 5% of the ingredients known as “character-givers” – which  modify the nature of the glaze.

Image 7:
Conclusions: each element changed the appearance of the basic recipe completely – they all succeeded, “opened up” and were glazed.

1. Chalk: came out white, perfect and clean. Surface is smooth and opaque.

2. Kaolin: created a brown-earthy color. Surface is relatively smooth, slightly granular.

3. Barium: white, semi-transparent color. Rough, even somewhat volcanic, bubbly and irregular surface texture.

4. Titanium: white, opaque color. Irregular and rough surface.

5. Zinc: murky-white color with small bubbles.

6. Magnesium: white, with separate “islands” typical of magnesium.

7. Lithium: gray. Surface looks like cracked glass. The material corroded some of the glass surface and created a crack in the glass body.

8. Strontium: opaque white but with many pinholes – small see-through bubbles.

Testing helps me map the nature of the glaze I get when I want to add each of these materials and achieve a different surface area. In addition to the visibility of the surfaces, I can add dyes (both natural and synthetic) to each of them, thus reaching a wealth of different and varied glazes.

Up to this point, the research was carried out in a constant temperature and in a regulated environment in a kiln, and I decided to do a few experiments in the hot workshop – a more challenging environment with variable heat – to see if the glazes could still contribute to artistic creation and the design of liquid glass. Contrary to the norm, by which glazing comes in a liquid state and saturated with water, in the hot workshop the water may create a thermal shock and therefore is not needed. The blown bubbles are rolled in a powdery mixture and the powder immediately adheres to the material. The glass bubbles were obtained in different colors thanks to the cobalt, chrome and tin, and have interesting textures such as floating islands or parched earth. I was delighted to find that these glazes could work in a furnace and might be able to replace glass dyes, reduce costs, and create a rich variety of textures.

Image 8: 1. Cobalt; 2. Tin; 3. Chrome

During the research, I discovered a whole world of interest to me: assembling glazes, learning about chemical elements and their mutual reactions. I was able to overcome the difficulties and challenges posed by the research, found the connection points between the materials themselves or between the working temperatures, and learned about all the options for fusing the glaze with the glass.

As a result of the research and the wide variety of options, textures and colors obtained in it, I formed a collaboration with Shaked Cohen, who created a series of turtles in print and slumping techniques. To this series we added one special turtle whose shell and body are covered with cracked grayish glaze.

Image 9: Shaked Cohen’s work

It is my belief that we achieved a breakthrough in a field that has not yet been explored and that can develop in many ways. The possibilities that the research opens in the field of glass lead to the creation of new textures on the material’s surface and to many new, interesting creations.

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Supplement: Performance graph

Temperature (in centigrade)	time
100	1 hour
800	6 hours
800	0.5 hour
515	0.5 hour
515	2 hours
370	3 hours
40	2 hours