C3 Five Glass Panels

Glass panel samples by Julia Rai
Glass panel samples by Julia Rai

Submitted to the Registry evaluators - November 2008

I love glass fusing so messing around with metal clay and glass was really good fun. I wanted to use some slumped glass panels with metal clay on the surface as well as doing some elements sandwiched together so I had a very pleasant few days experimenting with this. And I got full marks again for this project.

Innovation – 7.5 out of 7.5
Range of experiments – 2.5 out of 2.5

The comments were very encouraging too. “Great range of experiments in both glass and metal clay. Excellent written descriptions that will be helpful for further work. This is exactly what this project is intended to do – to award innovative thinking as it demonstrates the importance of experimentation.”

The panels on the left show the glass I used which had slumped grooves. I used syringe, slip and gold paste to paint or fill the grooves and fired them at a variety of temperatures. Writing up the experiments was as important to this project as the experiments themselves.

My experiments are below.

Three glass panels were made, approximately six inches long by two inches wide. Each panel was made from a single piece of Spectrum glass. Each panel has been slumped into a surface pattern through the following process:-

A pile of potter’s plaster was heaped onto a kiln shelf and then compacted into a neat pile with a flat top using a wooden board. The pile was approximately four inches tall and the flat top long and wide enough to accommodate one glass panel.

Using a deeply patterned commercial rubber stamp sheet slightly longer and wider than the glass panel, an indented pattern was carefully made in the flat top of the plaster. It took several attempts to lay the rubber stamp sheet down on the plaster, gently press it in and then lift it off to give a clean indentation. The lifting off was the trickiest part as it requires a smooth and even lift of the sheet to get a clean mold.

The glass panel was laid on top of the plaster with the indented pattern. This was then fired at 820 degrees for 30 minutes using a slow ramp and controlled cool to ensure the glass did not suffer thermal shock.

The result of this process was a panel of glass with a raised pattern where the glass had slumped into the plaster impression. Three panels were made using this process, each with a different pattern.

The glass panels were cut into sections making several panels approximately 2 inches by 2 inches. I then experimented with these panels with the following results.

Panel 1 – Red glass with lump metal clay inclusions

I pushed lumps of metal clay into the indentations in the glass and smoothed the top, making sure that the higher areas of the glass were free of clay. After leaving this to dry, I further refined the clay using a salon board. Some of the clay went up to the edges of the glass, other parts were completely enclosed in the indentations.

This panel was fired at a medium ramp speed of 555 degrees an hour to 700 degrees C for 30 minutes. It was then allowed to slowly cool.

The result of the firing was that the clay had sintered and was easy to polish with a steel brush. But the edges of the glass were still sharply angled where they had been cut. I decided to re-fire the panel to soften the edges. The danger of this was that the indentations in the glass would also soften and I was not sure if that would push the metal clay up and out.

I re-fired this panel using a slow ramp speed (250 degrees C) to 850 degrees C for 30 minutes.

The result of this was a softening of the edges but the indentations remained although less pronounced. The metal clay could then be brushed with a steel brush to bring up the shine. The glass that has come into contact with the metal clay has turned blue. The raised areas of glass have a glossy appearance which give a nice contrast with the metal clay inclusions.

Panel 1 – Conclusion

I was happy with the result of this experiment. The clay seems to be well bonded to the glass in the indentations. This may be because the indentations had a frosted appearance, having been formed face down in plaster. This rough surface may have acted as a key for the clay. The colour of the glass has changed from red to blue on the top of the piece and the glass retained a glossy appearance.

Panel 2 – Purple glass with painted gold paste

For this experiment I used ready made gold paste. First I used the paste undiluted, just stirred. This was very thick and I thought it would go on better. I painted this into the indentations in the panel but when I painted on a second coat it pulled the paste off the glass.

I diluted the paste with a little of the supplied medium and this flowed much better. In some areas I painted three coats, allowing each to dry thoroughly. In others I just used one coat. This can be clearly seen on the finished panel.

The gold looked smooth and even across the panels in the indentations. It was fired following the manufacturers instructions. The kiln was fast ramped to 800 degrees C then held for five minutes. It was then crash cooled to 600 degrees, the door closed and left to cool completely.

Panel 2 – Conclusion

​After firing the gold paste had cracked in the areas where several coats had been used. At first I was a little disappointed about this but I actually quite like the effect on reflection. I considered painting over the cracked areas and re-firing but decided against it. The glass had softened nicely at the edges and the indentations are still noticeable although they have flattened out somewhat. The gold polished up with a steel brush and seems well bonded to the glass.

Panel 3 – Purple glass with poured slip

I had a pot of well-used slip, made from filings and added to over many months on my workbench. It was pretty runny, the consistency of single cream. I decided to pour this into the indentations in the glass panel.

I fully expected it to run over the edges where the indentations were not completely enclosed but it stopped short of this. Again, I think that the slightly frosty surface of the indentations helped to hold the slip. I allowed this to settle, gently tapping the panel on the table to try and dislodge any bubbles. My original intention was to pour more slip into the indentations when the first layer had dried but I liked the slightly uneven surface of the dried slip so decided to fire it like that. I made sure the raised glass was clean of stray smudges of slip.

This was fired using a ramp of 555 degrees C an hour up to 700 degrees C for 30 minutes. It was then allowed to slowly cool.

The result of the firing was that the slip had sintered and was easy to polish with a steel brush. However, like Panel 1, the edges of the glass were still sharply angled where they had been cut. I decided to re-fire the panel to soften the edges. I hoped that I would have the same result from the re-firing as I had with Panel 1. I re-fired this panel using the same ramp speed to 850 degrees C for 30 minutes.

The result of this was a softening of the edges and the indentations remained although they were less pronounced. The glass has taken on a frosty, matt appearance in contrast to Panel 1 which retained a glossy appearance.

Panel 3 – Conclusion

​The surface of the slip has kept its bumpy texture, probably the result of lots of foreign bodies in my trusty old slip! It polished up with a steel brush and seems well bonded to the glass. I am pleased with the result here. It would be interesting to see how the result would differ with fresh, clean slip but I like the character the bumps give the finish. I was surprised that the glass has gone frosty and matt on the surface. The back of the panel has retained the glassy appearance.

Panel 4 – Red glass with syringe clay

For this panel I decided to use syringe clay and extrude the clay into the indentations. This was a quick and simple process. I allowed the clay to dry then it was fired using a ramp of 555 degrees C an hour up to 700 degrees C for 30 minutes. It was then allowed to slowly cool.

The syringed lines retained their rounded shape and the glass had also retained the indentations but as before, the edges were sharp as the temperature was not high enough for the glass to soften.

This panel was re-fired using a slow ramp speed to 850 degrees C for 30 minutes. The result of this was the edges softened and rounded and the indentations also flattened out. I believe this is because the syringed lines were very fine and had no real weight, unlike Panel 1 with the lump clay and Panel 3 with slip. Both these panels withstood the re-firing at a higher temperature and retained their indentations to some extent. The glass that has come into contact with the metal clay has turned blue, which makes a nice contrast with the surrounding red. There are also some frosty, matt areas and some glossy areas on the finished panel.

Comparing this to Panel 2, the gold paste painted panel, the time and temperature of the firing is probably a factor. The gold paste has no real weight or mass, like the syringe lines. Panel 2 was fired to 800 degrees C and held for five minutes. This was enough to soften the edges and sinter the gold but not enough to soften the whole panel so the indentations retained some of their integrity.

The slow ramping, 50 degree higher temperature and hold of 30 minutes is too much for a panel without fairly solid inclusions.

Panel 4 – Conclusion

My conclusion is that 700 degrees C is not a high enough temperature to soften the edges of the cut glass enough for them to be safely handled.

In the re-firing, I think it is fairly safe to say that time and temperature was the defining factor in the result of this experiment. A panel with fine syringe lines in the indentations requires a slightly lower temperature and shorter firing time to soften the edges of the glass without collapsing the indentations. Next time I will fire the piece from scratch to 800 degrees C using a medium ramp speed (500 per hour) and hold for 5-10 minutes. This should be sufficient to sinter the syringed lines, soften the edges of the glass and retain the indentations.

Panel 5 – Purple glass with pre-fired metal clay paper and thin metal clay inclusions

​For this experiment, I fired small pieces of metal clay paper cut into various designs using wavy scissors and small cutters. I also rolled out very thin clay sheets (1 -2 cards thick) and cut our small shapes. These were fired and gently brass brushed to a shine.

​Using tweezers, I placed these pieces of silver into the indentations. I cut a piece of clear Spectrum glass with approximately five millimetres of overlap all around and placed this on top of the glass panel. My intention was to trap the silver inclusions in the indentations by fusing the clear glass over the blue panel.

​This panel was fired using a ramp of 555 degrees C an hour up to 700 degrees C for 30 minutes. It was then allowed to slowly cool. During the ramping cycle, I heard a cracking sound from inside the kiln so I knew something had happened before I opened the kiln.

​The clear glass had slumped a little over the edges and was lightly tack fused to the high spots on the lower panel. A crack was visible across one corner of the clear glass. This was across an area that had the thickest silver inclusion. I am not sure if the crack was a reaction to the thicker silver inclusion, a result of a medium ramp speed or a result of trapped air expanding as the glass slumped. It may have been a combination of all these factors. As I was using Spectrum glass for the top and bottom pieces, I do not think it was a COE issue.

​The edges of the clear and blue glass panels were still sharp. I decided to re-fire this panel at the higher temperature to see what would happen. The second firing used a slow ramp speed (250 degrees C) to 850 degrees and a hold of 30 minutes. It was then allowed to slowly cool.

​This resulted in a full fuse of the glass trapping the silver inclusions. It also resulted in another crack developing on a corner of the panel. While washing the kiln paper off the panel, both cracked corners fell off.

​I fired this panel again at 800 degrees C for 30 minutes to see what would happen. The edges rounded out but another crack developed across the piece.

Panel 5 – Conclusion

​The inclusions in this panel seem to be having an effect on the integrity of the finished piece. Cracks developed at each stage. I am now wondering if the clear glass piece I used for the top of the panel has a different CoE from the bottom panel. I have successfully created cabochons with metal clay inclusions in the past without this cracking. I consider this panel a failed experiment but I will recreate this panel at a future date with clearly marked glass to ensure the CoE is the same.

​Panel 6 – Red glass with metal clay paper inclusions

​Metal clay paper was cut into interesting shapes corresponding to the shapes of the indentations in the glass. This was achieved by lightly pressing the metal clay paper sheet over the glass panel then putting two folded pieces of kitchen paper on top to act as a cushion. On top of this I put a pile of kitchen crockery to act as a weight. This was left for 24 hours. The result was a piece of metal clay paper embossed with the indentations. Using a sharp craft knife, I cut the main shapes and placed them into the appropriate indentations or raised areas.

​This was fired using a medium ramp (555 degrees) to 800 degrees C and held for 30 minutes.

​My aim with this experiment was to see if the paper clay would adhere to the glass when it fired. I wanted to see if the metal clay paper shapes would adhere to the slightly frosted glass indentations in the same way the slip and clay did in earlier experiments. I also wanted to find out what would happen to the paper clay laid on the raised surfaces.

Panel 6 – Conclusion

​Two of the paper clay pieces appeared to be fixed to the glass but when I brushed them they popped off. The other inclusions remained fixed to the surface and seem to be fine. Running a finger over them, I can feel the edges and points of a couple of the inclusions. This suggests that with any significant wear, these would also fall off. To use this piece, I would re-fire with a clear panel on top to trap the silver inclusions. I am leaving this as is for the purposes of this experiment.

​Two experiments were undertaken using Bullseye glass.

​Panel 7 – Clear/green glass with embedded lentil bead

​I had a fired lentil bead and decided to embed this in glass to see what would happen. The lentil was textured using a tear away sheet so the texture was shallow and subtle. Because the lentil is domed on both sides, I knew this would be difficult to fire as a horizontal sandwich.

​The kiln posts were wrapped in kiln paper and formed a rectangular vessel for the glass. I propped up two panels of clear glass on either side of the vessel, then put clear and green stringers broken into pieces at the bottom. I propped up the lentil bead on the stringers, sandwiched between the glass panels. I filled in the top with stringers.

​This was fired at 800 degrees C for 30 minutes using a slow ramp up and then allowed to cool in the kiln overnight. When I unpacked the kiln, the sandwich had fused together but was not fully fused and was quite crude. I refired the panel laid down flat on the kiln shelf using the same schedule. The result of this was a panel fully fused with the lentil in the middle.

Panel 7 – Conclusion

​This was a very interesting experiment. The challenge of embedding the domed lentil in the glass led me to do the initial firing vertically. This was a feat in itself and took me considerable time to get right. The lentil completely lost its texture although you can still see the hole I’d made in it. A large bubble has formed underneath the lentil and there are a couple of other bubbles in the glass.

I’m surprised that the lentil remains suspended in the glass. I expected it to drop to the bottom of the vertical panel when the glass became viscous, particularly considering the weight of the lentil. I conclude that it didn’t because the firing was too short and probably not hot enough. The result of the first firing was a very crude light tack which required a second firing for full fusing.

It’s hard to tell if the lentil has retained its doming or flattened out. It looks flatter but this may be an optical illusion. I would like to do more of these vertical fusing experiments to refine the technique. My questions include what would happen if I used a hotter, longer firing with the vertical firing. Would the inclusion drop to the bottom or remain suspended as happened in the experiment. Could I achieve a full fusing with a vertical configuration?

Panel 8 – Blue square with fired paper clay inclusions and a hole

​This experiment combined fired paper clay inclusions with making a square donut shaped glass panel. Blue glass was cut into strips and squares then placed in a square formation with a hole in the middle. Fired pieces of paper clay, brass brushed, were placed on top. Then clear glass was cut in strips and squares and placed on top of the blue glass. This was fired for 30 minutes at 800 degrees.

​Panel 8 – Conclusion

​This was a successful experiment with the donut forming well and the paper clay inclusions remaining silvery. In contrast to Panel 5, this panel didn’t crack during firing. I put this down to only using the very thin paper clay inclusions for Panel 8. I was also very sure that both top and bottom layers of glass were Bullseye.

Overall Conclusions

​Panels 1, 3, 4 and 5 were fired together on the first firing. 700 degrees C for 30 minutes is not a high enough temperature to soften the edges of the cut glass enough for them to be safely handled so they all required re-firing.

The reaction of the glass indentations at the higher temperature was interesting. Panels with heavier inclusions managed to retain their indentations to some extent at 850 degrees for 30 minutes. The lighter slip inclusions were not sufficient for the glass to retain the indentations at this temperature.

​The challenge of embedding a lentil bead for Panel 7 made for some interesting times in my workshop! It was great fun working out how to do this and seeing the results.

​The square donut shape was an interesting project to attempt. I’m glad it came out well and will use the method again. Including the fired paper clay elements was also successful and allowed me to learn from the mistakes of Panel 5.

Although this project requires five panels to be submitted, I’ve sent six which I feel reflect my learning from this exercise. I’ve submitted Panels 1, 2, 3, 4, 7 and 8.

​Here is the description of this project from the Masters Registry website:-

​C3 Five Glass Panels

Make at least five separate glass panels, each approximately two inches square, embellished with slip, paper, and other forms of metal clay. These are not wearable or functional. The purpose of this project is to encourage experimentation and innovation. Successful candidates will not stop at five experiments, but will alter layers, inclusions, firing times, and types of glass as much as needed to develop five interesting samples. Proper note keeping will allow duplication, so a written description of materials and the process of each test should accompany the samples.

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