Foxden Posted April 30, 2016 Report Share Posted April 30, 2016 I am making a somewhat large ceramic globe (15 inch) as part of an outdoor garden sculpture. I built it from slabs around a big inflatable ball I purchased at Walmart. I can lessen the inflation of the ball as the clay firms up to prevent it from cracking as it shrinks, but I am now wondering about removing the ball or letting it burn. Deflated, the ball will probably come out of a 3-4 inch opening I can cut into the globe when it's leather hard OR I can just put a small hole in the globe for ventilation and let the plastic ball burn out. I know burning combustibles can shorten element life, but is just this once really going to be an issue? The kiln is located in a separate facility so we wouldn't be breathing any fumes from the burning plastic. Making pots for over 20 years and still have unique situations to deal with. Your advice? Link to comment Share on other sites More sharing options...
Babs Posted April 30, 2016 Report Share Posted April 30, 2016 Don't know your question's answer but I made a number of molds using vaselined balls, mold in plaster to half way, ie hemispherical, make two with lock in keys. Can make any sized molds from balls like this and join at leather hard or just a tad softer. Gets around this prob for the future, and you don't have to keep releasing air, so reduces the error factor. Can carve etc these orbs later. Lots of possibilitiescoil build then and leave the outside showing coils. Great use of soccer, netball, basketballs. Schools sometimes have supplies of old balls that you "borrow" then donate to the ball obsessed dogs of the world. maybe placing the pot in a sagger will reduce element damage, but I don't have the scientific knowledge to back this. Just thinking that some of the gunk will be depostited first on the sagger.... Link to comment Share on other sites More sharing options...
Foxden Posted April 30, 2016 Author Report Share Posted April 30, 2016 I had thought about making a plaster mold and assembling the two hemispheres. I will likely follow that route if I need to make any more, but this is a one time project. Of course if it cracks or fails the mold will be my next try. Link to comment Share on other sites More sharing options...
Magnolia Mud Researdh Posted May 1, 2016 Report Share Posted May 1, 2016 Just recently went through an assignment requiring making spheres. Used several techniques. Throwing spheres is not that complicated unless you need the sphere to be thin walled. Students in class used press molds, hump moles, balloons, and hallowing out solid balls; all worked at least on sizes up to about 12 inches diameter. Drying is slower than a bowl or cylinder. Removal of the ball would be the best option. Getting oxygen into the sphere to burn the plastic is likely to be incomplete unless you deliberately force air into the sphere while firing. If the plastic is not completely burned it will likely cause problems in the glaze firing. I see two options, equally tedious. 1. cut a big hole - the 3 to 4 inch you estimated and replace or 2. cut the sphere in to two pieces and join the pieces back together. (think slicing a pieces off the top). I have seen both work, but personally lean toward option 2. I suggest that after removing the ball you make two small holes - one top and one bottom - about 1/4 or 3/8 inch size to improve drying. LT Link to comment Share on other sites More sharing options...
Marcia Selsor Posted May 1, 2016 Report Share Posted May 1, 2016 I wouldn't burn rubber/plastic in a kiln. Very toxic. Marcia Link to comment Share on other sites More sharing options...
Foxden Posted May 1, 2016 Author Report Share Posted May 1, 2016 I intend to deflate it fully and remove it. Marcia and her various firing techniques certainly make her an expert in fumes. If they are toxic in her book, I'll heed her advice. Link to comment Share on other sites More sharing options...
Babs Posted May 1, 2016 Report Share Posted May 1, 2016 The advice given to cut it in half to remove the ball is the best one. Cutting a hole and then trying to remove the ball through that hole will end up a little more difficult than you think. Would work with a balloon but the rubber ball would not compress that easily imho Link to comment Share on other sites More sharing options...
Foxden Posted May 1, 2016 Author Report Share Posted May 1, 2016 These balls are more like a beach ball. I saw it before they inflated it in the store. It isn't made like a basketball, although it is larger. I think I can get out of a 3 inch opening. I think, that is. Your suggestion is my plan B. Link to comment Share on other sites More sharing options...
Foxden Posted May 2, 2016 Author Report Share Posted May 2, 2016 I need closure when I can get it, so here's the story and a couple of photos. The ball came out pretty easily through about a 3-inch opening. I attached a picture of the leather hard clay ball and the plastic ball once removed. I did need to draw some air out of the ball to really get it deflated but that was a breeze. Good lungs I guess. Link to comment Share on other sites More sharing options...
oldlady Posted May 2, 2016 Report Share Posted May 2, 2016 thanks for the follow-up. Link to comment Share on other sites More sharing options...
Babs Posted May 2, 2016 Report Share Posted May 2, 2016 Hey, well done! Sure it's gonna be a one off? Link to comment Share on other sites More sharing options...
Foxden Posted May 3, 2016 Author Report Share Posted May 3, 2016 No, now I plan on making another one and carve openings all around, lit on the inside with an outdoor LED light. I love challenges and that ought to make the bone dry form extra fragile. This method allows for relatively thin and even walls. Link to comment Share on other sites More sharing options...
rayaldridge Posted May 3, 2016 Report Share Posted May 3, 2016 I wouldn't burn rubber/plastic in a kiln. Very toxic. Marcia I agree. Even if you have a vent, you're just polluting your neighbors' air. Link to comment Share on other sites More sharing options...
AndreaB Posted May 4, 2016 Report Share Posted May 4, 2016 No, now I plan on making another one and carve openings all around, lit on the inside with an outdoor LED light. I love challenges and that ought to make the bone dry form extra fragile. This method allows for relatively thin and even walls. Sounds like fun Link to comment Share on other sites More sharing options...
JudyM Posted May 10, 2016 Report Share Posted May 10, 2016 Foxden, could you explain your technique in making the ball - I am only new to ceramics and would love to know the steps - btw it looks great👌 Link to comment Share on other sites More sharing options...
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