This all depends on your recipe.

using your kitty litter container sounds good. I have used different plastic type containers, I line mine with a plastic bag first. For the hole or holes I use a 1/2"-3/4" thick closed cell foam (not sure that is really what it is called) cut to the shape that I want the opening to be, then using eye screws I screw through the plastic container, and position the foam.One screw holds the foam in place. I can then pack my tufa mix in the bottom and up the sides to the foam, then in between and over the top of the foam. The foam acts as sort of a gage for how thick I want the lantern to be. At some point I often put a smaller plastic bag covered container (as tall as the lantern will be) in the opening, so that I will retain a more uniform void. Continue up the side an inch or more. Then place sand in the inside container, just to hold it in place. Cover with plastic, for a day or more. To release it, unscrew the eyescrews. Remove the center container. Gently wiggle the entire lantern out with the plastic, and then roll the plastic down. Depending on how soon you released it you will be able to rough up the surface a bit if that is your preference. Gently push the foam out, I can reuse my foam pieces. I also do some clean up carving of the spaces at this time with an old serrated knife.
Hope that made sense,
Happy casting,
Dena

Hi, mpasserr,

Are you thinking about casting a solid block in the kitty litter bucket and then carving out the center and the lantern windows? I plan to sand cast a lantern in a similar manner in the spring.

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Here is the inside of a sand cast rectangular planter that I carved out (well, more like scooped out actually).

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Here is a cone torch that I sand cast with an 'accidental' window. When I was carving out the space for the torch, I hit a patch of perlite and ended up making a hole in the side of the cone. Hey, I liked it, so I carved it into a little window.

With a mix of 1 part cement, 2 parts sand, and 2 parts perlite, I wait about 3 hours after casting to start carving. But that's casting in a sand mold and leaving the casting in the mold when I do the initial carving.

Eva

P.S. Hi, Dena and David!

Here is a link that might be useful: Sand Cast Bowl and Planter with Carved Spaces

Im really interested in doing a Japanese lantern but seem to be having great difficulty in finding proper plastic ware to use as molds. Making me think that either carving from a block OR making forms from foamcore board or foam insulation might be a better alternative.

Use Blue styrofoam.
Home Depot will sell you a 2'x8'x1.5" sheet for a few dollars.
You can cut it into any shape you wish, make boxes, etc.

I used a method similar to Dena when I made my Japanese-style lantern, which is pictured in the gallery. I cleaned things up with a wire brush and old rugged wood rasp.

I used cheap plastic ware (a square plastic bowl, and square top/round based garbage can) and used the blue styrofoam mentioned above to make the windows in the lantern body and arches on the lantern base. I used heavy duty double stick tape to hold the styrofoam in place, (I love those molds and don't want to damage them!)

I have seen the bowl at the Christmas Tree Shop and possibly at Mal-Wart, where I regularly troll for interestingly-shaped plastic molds! I also find great molds at yard sales.