Pottery questions


Most of my pottery knowledge is theoretical rather than practical, but here's a few things to think about.

The amount of sand depends on your clay - a very pure high quality clay source might need more sand than a lower quality clay that already has a good bit of silt and sand in it. You're probably going to have to experiment. Make a few small simple pinch bowls using clay with 5, 10, and 15 percent sand (for example), fire them, and see which ones turn out well. The sand you use will also make a difference. Some sand is water tumbled (beach sand, river sand bars) so much that it's basically lots of little spheres, the lack of corners means it doesn't stabilize the clay as well. Other traditional materials you can try are shell (freshwater mussel or sea shells) pounded fine and grog - grog is good because you can recycle any failed/broken ceramics into grog to temper the next batch by pounding them down into fine particles. I've seen grog temper that ranged from fine sand to the size of peppercorns.
 
I was planning on grinding down the sand from a wash bed... would that be okay... I want to make an oil lamp so the less porous the better.
 
I always use grog with my pottery clay and foundry/forge/kiln refractory. Old coffee mugs, plates, bricks or any other ceramic/pottery that has already been fired works terrific. Just remember it has to have already been fired.

If you don't have any, just make up a few discs of clay and fire them, they will break, crack and crumble, but thats okay because your just going to break them up and pound them into a powder any way.

Mix your newly made grog powder with your sand and clay while dry and then add water slowly, mixing and kneading the whole time.

After you get the consistency you want, cover the clay and let it set for at least 24 hours. You might think this step isn't important, but it makes a HUGE difference in the clays elasticity and workability.

Good luck and have fun!
 
Peacelovingirl said:
I was planning on grinding down the sand from a wash bed... would that be okay... I want to make an oil lamp so the less porous the better.
Click to expand...

To make pottery that was able to hold water/oil without it seeping through the pores, the Cherokee used to fire the bowl or vase with corncobs on the inside. Something with the oils in the cob seals the pores in the clay.

To make it fully water proof you need to make a glaze for the pottery after it has been fired. Paint the glaze on the fired pottery after it has cooled and re-fire the pottery.

A simple glaze can be made with crushed glass beer/soda bottles, borax and water. Mix the powdered glass with a little water until it's a milky consistency and then paint it on to the pottery. Allow the glaze to dry, then fire.

If your really interested in pottery and the old ways of how it was done, I highly recommend the following reading material. It can be found at the Internet Archive and is free to download. :-)

Pottery; a hand-book of practical pottery for art teachers and students by Lunn, Richard
http://www.archive.org/details/potteryhandbooko02lunniala

Pottery, for artists, craftsmen & teachers (1914) by Cox, George James
http://www.archive.org/details/potteryforartist00coxgrich

and

The chemistry of pottery (1895) by Langenbeck, Karl
http://www.archive.org/details/chemistryofpotte00langrich

Between these few books, most if not all your questions on pottery, mixes, ratios, glazes, glaze recipes, how to fire, build a kiln, and firing times will be answered.

Good luck and have fun!
 
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Well... I did some pottery for a challenge a while back and since have done a bit more.

I temper my clay with about 1/8 sand or something like that. I think that different clays will act differently so you may want to try some small samples to get the ratio just right.

As far as firing, I dig a fairly large pit and once the clay is very dry, I put it in the center of the pit on a flat rock with hot coals all around it. Then I build a fire all around and even on top of the clay (not sure if I'm making sense here or not) basically you want the entire piece engulfed in a hot fire. Keep it burning furiously for about an hour or so, and then let the fire die down with your piece inside. You want the clay to cool with the fire completely so that you pull the piece out of the cool ashes with bare hands this allows the clay to cool at the same rate as the coals of the fire and not change temperatures rapidly as it would if you pulled it out hot and set it in the cold ground in the cold air.

I don't know if I was able to help, but there's some tips based on my VERY limited experience.

Ed
 
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