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Wednesday, September 24, 2008

Notes on terra sig - part 2

In part 1, I talked a little about proportions of clay and water and basic clay prep.

Deflocculants will definitely improve your results over mixing only clay and water. What they do is help separate all the individual clay particles and keep the smaller particles of clay suspended until the larger particles settle out. What to use is a whole other matter.

By far, the most recommended deflocculant for terra sig is sodium silicate. It's very effective, and only a few drops are needed. Other choices include soda ash and tri-sodium phosphate (TSP).
For my first experiments, I used TSP since it was readily available at the local building store as a cleaning agent. Make sure you get actual TSP, and not TSP substitute. I used about a teaspoonful in a gallon or so of slip and it was plenty. Later I used about a tablespoonful in a 3 gallon batch of red sig slip.

So then you mix well - I used a paint mixer attachment on an electric drill for a few minutes.
Depending on the clay you'll usually see an almost oily appearance to the surface when you stop stirring from the fine clay on top of the water.

Then walk away. Let it sit. 24 hours minimum. My first try didn't sem to be separating into distinct layers, so I let it sit for 3 days.

You'll either get layers or not, but either way you'll then want to carefuly siphon off either the top 2 layers, leaving the heavy third layer behind, or siphon off the top 1/2 to 2/3 of the liquid if there isn't distinct layering. This is the terra sig you've been after.

You'll need to experiment with the consistancy. As I said earlier, my first batch used WAY too much water, so I had to evaporate some of the water away to get a usable product. I actually poured it into an old bisque bowl I had laying around which let it evaporate and also absorbed and wicked away water through the bowl.

Next time - Future testing


cynthia said...

Interesting - I don't know a lot about terra sig. Do you have any images of your finished tests?

Brian said...

Not really in one place.
If you click on 'terra sig' in the Tags section of the right column, it'll bring up all the posts that have pics of my sig pieces. You can click on the photos and it should bring up a bigger version. The shiny ones have sig, there are a few pots mixed in that aren't but they're noticeably duller/drier looking.
The white ones in this post:

are before being saggar fired. The third pic down has a sig piece on the left, 'normal' stoneware on right.

cynthia said...

Thanks - going to check them out now....