Post #740625 by MadDogMike on Thu, Apr 2, 2015 9:08 PM

I made a new type of volcano bowl, more low and flat than the traditional volcano bowl. It is actually a water dish for our new iguana enclosure :wink:

Tried something new for the "lava", Amaco black Arroyo glaze over Mayco Wildfire Jungle Gems glaze. Looks like the lava has partialy cooled and formed a crust over the top but you can still see the glowing orange in the cracks. Also has a cool texture.

CLAY OVER STYROFOAM TUTORIAL
This is a technique I use frequently, might as well share it. It works well for one-off items that are odd shaped. Much easier than building the object hollow or building it solid then splitting it and hollowing it out. I use the white Styrofoam from Lowes or Home Depot, about $12 for a 4x8 foot sheet of 1 inch thick. Take a sharp knife to the store with you, score and break the sheet into managable sized pieces in the parking lot to fit it into your car. You can cut the foam with a saw or knife or use a handheld heated wire tool available at Michael's or JoAnns. Stack the pieces of foam as needed to make the desired size blank. Dampen the pieces with water, glue with a small amount of Gorilla Glue and secure with a bamboo BBQ skewer (the water causes the Gorilla Glue to harden). After the glue is cured, remove the skewer and sculpt with a Sur-Form rasp. Sculpting will make a HUGE mess, I usually do it outside over the dumpster.

I aways use paperclay for this technique, it shrinks less than regular clay as it dries and is less likely to crack against the foam core. Roll the paperclay into a slab the desired thickness and cover the foam core. Trim excess and add pieces to cover foam as needed. Press the clay against the foam but be careful not to press too much as it will thin the clay.

After the clay has dried and firmed up a bit, texture the clay as desired. I tried something new for a rock texture this time. I usually take a piece of lava rock and "pounce" it into the clay. But you have to keep turning the rock or the texture starts to look too much the same. This time I took a roundish lava rock and rolled it around on the clay in several different directions, made a more believeable rock texture.

OPTIONAL STEP -
In theory, there is no reason to remove the Styrofoam core. Paperclay doesn't shrink much as it dries and the paper fibers help make it stronger. I have done several that I left the foam core in with no problem but I did have one crack while drying. I think it may be because I used the more dense blue Styrofoam and it didn't "give" as much when the clay dried. So now I dissolve the foam core with acetone, it provides a little safety and make me feel like a mad scientist :lol:
Once the clay had dried enough to be self-supporting, you can start by pouring a little acetone fingernail polish remover on the foam. The acetone doesn't seem to harm the clay but dissolves the foam. Keep pouring the acetone on the foam a little at a time until the foam is mostly dissolved. You don't have to get rid of ALL the foam, just enough to weaken the structural integrity so it flexes if the clay shrinks.

With or witout dissolving the foam, it is ready to fire once the clay is completely. Hopefully your kiln is outside because it is going to stink and release some possibly toxic fumes. The foam will burn up leaving nothing but ashes. One caveat is that the inside of the piece (that was against the foam) will have a rough texture. Depending on your design, you might be able to smooth the inside some if you disolve the foam out?

Now the piece is bisque fired and can be treated in the normal fashion. Have fun! Here are some other pieces I have made using this technique.