I unloaded the soda kiln today to get out these glaze tests I did to help correct the crazing. I kept the color variable the same in the test so at least I can see that is consistent. I'm happy with the color, only the things I tried to decrease the crazing (cracks in the surface) didn't really show up because the soda we put into the kiln worked against me! It creates even MORE crazing. So I can't win! Every single tile looks pretty much identical, so I can't even detect which portion that I altered in each test worked or not. I'll at least try some more in my next large kiln load that I fire, which will be a couple months. This so called crazing problem might not even be a problem when it's a liner inside a bowl in an area where not as much soda comes into the kiln. So we'll see....on with the testing, right?
I unloaded the soda kiln today to get out these glaze tests I did to help correct the crazing. I kept the color variable the same in the test so at least I can see that is consistent. I'm happy with the color, only the things I tried to decrease the crazing (cracks in the surface) didn't really show up because the soda we put into the kiln worked against me! It creates even MORE crazing. So I can't win! Every single tile looks pretty much identical, so I can't even detect which portion that I altered in each test worked or not. I'll at least try some more in my next large kiln load that I fire, which will be a couple months. This so called crazing problem might not even be a problem when it's a liner inside a bowl in an area where not as much soda comes into the kiln. So we'll see....on with the testing, right?
4 comments:
Morning Joy-
Couple ideas to help with crazing: first off remember that anytime you are tossing a glazed pot into a soda kiln, you have to account for that ADDED sodium. Sodium based glazes craze a TON. So, what to do, drop some of the sodium(or other KNa fluxes) OUT of the glaze. Another way of looking at this, RAISE the melting point of the glaze by increasing the Si:Al2O3 ratio.... (dry out the glaze).
Another issue is that some fluxes craze more than others. Magnesia,Strontium, Lithium and Barium all contribute LESS to crazing. So, consider replacing some of your feldspar with small SMALL amounts of things like talc, magnesium carb, strontium carb, etc. It may initially cause MUCH greater fluxing, and the glazes may move more. If that happens, increase the amount of clay/silica in your glaze (ie, raise the maturing temp of the glaze)...
When I did a ton of salt/soda firing all my glazes had to be reformulated for soda/salt. I kept my 2 fave liner glazes, allowed them to overlap the outer glazes just at the lip. Made for a nice decorative element, but inside the glazed pot everything was fine.
More on color development and bleaching next time.
cheers and GOOD LUCK!!!
It's so funny, I got all this crazing on my raku test tiles and was so excited about it. The glazes that didn't craze were a disappointment. I personally like the crackle look but I know it's not too good for functional pieces. Good luck!
Tracey- I love the crazing too, actually, just not inside...It's funny how we get so picky about our expectations. Your raku tests look great!
Alex- Thanks for the tips. One of the tests I did increase the silica, another one I increased the lithium content either 1. by adding more lith. carb., and 2. adding spodumene instead of half of the F-4. But, I didn't think about the F-4 that is in the glaze. So maybe I'll try a round with Custer. I was afraid to try the mag. carb route or talc b/c I thought that might change to a more matte surface? I'll try though, and of course, always remember that the soda is working against me, but it's certainly worth it on the outside of the piece! There already was some lith. carb and strontium in the glaze so I thought that would help by trying to increase those. I'm still looking closely at my tiles to look for subtle differences, they MIGHT be there. Good idea to switch out the soda spar.
Another thought I had is to throw them in a non soda firing just to see where I am on the level of crazing and then I'll really know if this glaze should be in a "quiet" place in the kiln. Since I fire in a crossdraft, there are drier areas where this might work.
Adding MORE fluxes wont solve the problem. Adding clay might. Adding silica and clay might. Changing the fluxes might. More flux just means a lower eutectic. So, more crazing!
Try adding 2-6% ball clay. In 1% increments, to the same glaze. You will probably see the crazing stop between 2-3% added ball clay.
The lithium and mag carb route will DEFINITELY give you different surface texture. Potentially rich satins and mattes. Very different color response too.
Good luck.
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