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Artwork (Traditional) / Fantasy
Species Eastern Dragon
Size 1280 x 427
File Size 120.4 kB
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So this....... If you want to know what's been eating up my time and driving me up the wall, this guy is it.
Let me tell you a little story; my school has one of the best sculpture-labs in the area, we even have a five-foot electric kiln! So when I had to sculpt an animal for my sculpture class last quarter I decided that bigger was better, and made this guy. Over the course of the two months I've had to work on him he has broken a total of four times and I have had to resize him just to fit into the kiln a total of three times.
When I say this guy is epicly huge, I'm not exaggerating. My teacher and other faculty members in the lab have commented that this is the largest project they have seen attempted in their career, and not just for the size of the kilns but for also for the tensile strength of the medium. I have literally pushed this clay to its absolute limit in both form, size, and stability.
So here we have two pictures of him from the side. I attempted to sculpt every single scale but at the fourth repair I had to cut my losses and determined that having most of the scales rendered would have to do. (Not to mention the fact that my technique for sculpting the scales was what made the sculpture so weak in the first place.)
Originally I had planned on glazing him so that he would be able to stay outside for the summer months and guard our garden, but I have a deadline to keep and keeping the deadline means that I will probably only have time to fire him once and then paint him.
So the lesson I learned was that a big dragon can be big trouble!
Let me tell you a little story; my school has one of the best sculpture-labs in the area, we even have a five-foot electric kiln! So when I had to sculpt an animal for my sculpture class last quarter I decided that bigger was better, and made this guy. Over the course of the two months I've had to work on him he has broken a total of four times and I have had to resize him just to fit into the kiln a total of three times.
When I say this guy is epicly huge, I'm not exaggerating. My teacher and other faculty members in the lab have commented that this is the largest project they have seen attempted in their career, and not just for the size of the kilns but for also for the tensile strength of the medium. I have literally pushed this clay to its absolute limit in both form, size, and stability.
So here we have two pictures of him from the side. I attempted to sculpt every single scale but at the fourth repair I had to cut my losses and determined that having most of the scales rendered would have to do. (Not to mention the fact that my technique for sculpting the scales was what made the sculpture so weak in the first place.)
Originally I had planned on glazing him so that he would be able to stay outside for the summer months and guard our garden, but I have a deadline to keep and keeping the deadline means that I will probably only have time to fire him once and then paint him.
So the lesson I learned was that a big dragon can be big trouble!
Category Artwork (Traditional) / Fantasy
Species Eastern Dragon
Size 1280 x 427px
File Size 120.4 kB
The cause of fracture while firing is thermomechanical stresses. As a rocket scientist, I know a great deal about this problem. It takes time for heat to penetrate an object, especially one with low thermal conductivity such as a ceramic. During heatup, the outer regions are hotter and hence expand more than the inner regions, so the outer regions go into compression (ceramics are usually strong in compression), BUT this necessarily puts the inner regions in tension (where most ceramics are weak). During cooldown, the opposite happens, with the outer regions going into tension. The lower the temperature gradient from surface to interior, the lower the tensile stresses that cause fracture.
Since this is the largest piece that they have ever fired, the heating and cooling rates should be lower than they have ever used before. Try to talk them into an at least one week long very slow and gradual heatup and another at least one week long slow and gradual cooldown. If they can't tie up the kiln for that long while school is in regular session, see if it could be fired during the summer when the demand for the kiln might be less. Try to avoid firing during July or August when brownouts and blackouts are most likely; they aren't going to have emergency backup power for a kiln.
See http://en.wikipedia.org/wiki/Thermal_conduction , Section 1.2 Transient conduction
See also http://en.wikipedia.org/wiki/Heisler_Chart
As an approximation, you can think of your dragon being made of cylinders and spheres. Note that the temperature distribution with time is very non-linear, and that twice as thick takes a lot more than twice as long:
http://en.wikipedia.org/wiki/File:H.....ler_Zoom_4.jpg
http://en.wikipedia.org/wiki/File:H.....ler_Zoom_5.jpg
http://en.wikipedia.org/wiki/File:H.....ler_Zoom_7.jpg
http://en.wikipedia.org/wiki/File:H.....ler_Zoom_8.jpg
In fact, the thick stone (ceramic) walls of medieval cathedrals conduct heat so slowly that the outside winter cold reaches the inner surface during the summer, and the outside summer heat reaches the inner surface during the winter.
Please do everything that you can to persuade them to let you use the kiln for at least two weeks, one (or more) week for very gradual heatup, and one (or more) week for very gradual cooldown. The slower the better!
PS: The National Academy OF Engineering concluded that the reason that the twin towers collapsed so rapidly on 9/11 was thermomechanical failure; the very long steel floor beams heated up, expanded, and broke their connections to the walls, resulting in pancake collapse. Bigger means more vulnerable to thermomechanical failure.
Since this is the largest piece that they have ever fired, the heating and cooling rates should be lower than they have ever used before. Try to talk them into an at least one week long very slow and gradual heatup and another at least one week long slow and gradual cooldown. If they can't tie up the kiln for that long while school is in regular session, see if it could be fired during the summer when the demand for the kiln might be less. Try to avoid firing during July or August when brownouts and blackouts are most likely; they aren't going to have emergency backup power for a kiln.
See http://en.wikipedia.org/wiki/Thermal_conduction , Section 1.2 Transient conduction
See also http://en.wikipedia.org/wiki/Heisler_Chart
As an approximation, you can think of your dragon being made of cylinders and spheres. Note that the temperature distribution with time is very non-linear, and that twice as thick takes a lot more than twice as long:
http://en.wikipedia.org/wiki/File:H.....ler_Zoom_4.jpg
http://en.wikipedia.org/wiki/File:H.....ler_Zoom_5.jpg
http://en.wikipedia.org/wiki/File:H.....ler_Zoom_7.jpg
http://en.wikipedia.org/wiki/File:H.....ler_Zoom_8.jpg
In fact, the thick stone (ceramic) walls of medieval cathedrals conduct heat so slowly that the outside winter cold reaches the inner surface during the summer, and the outside summer heat reaches the inner surface during the winter.
Please do everything that you can to persuade them to let you use the kiln for at least two weeks, one (or more) week for very gradual heatup, and one (or more) week for very gradual cooldown. The slower the better!
PS: The National Academy OF Engineering concluded that the reason that the twin towers collapsed so rapidly on 9/11 was thermomechanical failure; the very long steel floor beams heated up, expanded, and broke their connections to the walls, resulting in pancake collapse. Bigger means more vulnerable to thermomechanical failure.
It's so awesome to have a technical, in-depth explaination of what's going on with my sculpture. My teacher explains that things happen with physics and chemistry when we cook everything in the kiln - but she's a sculptor not a physicist, so in the end it all comes out as, "just trust me on this one."
Slow is good when it comes to firing, and you've given me the solid facts on why that is.
Slow is good when it comes to firing, and you've given me the solid facts on why that is.
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