Wednesday, March 12, 2014
Work in Progress Wednesday: Grog tests
The only work being done this week in my studio is grog tests for tiles. It's not too exciting- though it is exciting to see the pattern play out over more than one tile (the bottom left hand corner has one wonky tile from the first mold I made- I just used it to get done a little quicker- it's total crap- so happy I squared things up). So you can see how the pattern will repeat- I'm pretty pleased with it- though the real test will come after it's glazed.
Okay let's get a little technical- I'm using Plainsman M390 clay for these tiles- mainly because it's what I use for everything else- it's a good plastic clay- that holds up well to hand building, and is really white once fired so it looks good with bright colour glazes. I'd like the tiles to be glazed with my regular glazes- so I don't have to worry about testing and formulating new glazes- so M390 it is. The only thing about this clay is that it's not grogged- and non-grogged clay leads to warping and irregular shrinking, and it's tougher to work with as a tile. So I'm opting to try and add fine grog (fired clay dust basically) to the M390. I'm also trying out some homemade paper clay (by wedging 1 ply toilet paper into the wet clay).
My method for adding the grog is to wedge it into wet clay- I know this makes my measurements a bit off percentage-wise- by adding dry grog to wet clay instead of dry grog to dry clay- I'll end up with a higher grog percentage, But all my percentages will be higher- so when I say 5 percent it's probably closer to 7, 2.5 closer 3.5 etc. Also I don't want to go to the trouble of mixing my clay from dry- unless I have to- I think it's safer for my lungs to work with the grog if I incorporate into wet clay because it's less dusty.
I started with 10 % dry grog ( 100 g grog - 1000 g wet clay) It was difficult to wedge in, and not very plastic, the clay got very dry, fast, it was unworkable. I diluted the 10% mix down to 5% by adding another 1000g wet ungrogged clay. The 5% clay was slightly dry, but as a result it came out of the mold quickly, and it dried nicely, the 2.5 % was not as quick to unmold- but it was a bit smoother- and dried down more, the.75% was smoother still- but also not as quick to unmold- it was the most like working with plain M390.
So far I like the 5% the best; the tiles dried very flat- they felt more solid and thicker right from the mold- they could handle a bit of sliding and flipping without deforming. My only concern is on how the grog will fire- Straight from the bag it looks grey- and I wonder if I'll be left with grey flecks in the white tile. That's why I'm also trying Paper clay (clay with paper fibers in it)- which would undoubtedly fire white.
Also I'm using a trick to help the tiles dry flat- waxing the edges with wax resist- so that they dry more slowly than the center. This works great for me, I've gotten the plain M390 tiles to dry flat with waxed edges and careful covering- but I'd rather have a sturdier clay mix so it's not as finicky. Next I'll get my paper clay samples done, and then make a bunch of stuff to fill the kiln so I can get firing these guys.