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Rough surfaces


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#1 kheicksen

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Posted 11 June 2013 - 04:44 PM

Hi,

I have am a newbie and having issues I would love your thoughts on.

I started with earthenware - mostly white, but also some sandy red. Every firing and every glaze I used, except for one firing using the same glazes, have had pinholing problems - multiple glazes, all commercial, and multiple clay bodies. I brush my glazes. I have used different types of brushes, including foam brushes. The kiln I have been using is a used Duncan Artists +, small in home electric. It uses a kiln sitter and has a timer but no peepholes. I tried leaving the kiln to cool for 24 hrs after firing as well as propping the lid at the beginning to allow gasses to escape. I can't get a piece to come out with a smooth surface. I am really frustrated.

Now I have moved on to midfire stoneware. All the clay I have been using is quite sandy. I thought that glazing would create a smooth surface over the natural roughness of the clay. Once again I am brushing commercial glazes. My surfaces are even rougher after firing. It almost looks like pinholing but I think its just the sand in the clay. I even burnished a piece before glazing it, and its still rough with a clear glaze over it. Its almost like the glaze enhanced the rough texture. Seriously frustrated. What should I try next? I have a lot of sandy clay and I want to use it.

I don't know if it matters, but the clay is all Laguna clay. Also, not sure if it is relevant, but the earthenware comes out of the kiln sounding like stoneware or porcelain when you strike it... . . Not sure why. Its still very absorbent.

Are my rough textured glazed stoneware pieces that are made with food safe materials actually food safe? What about the pieces with pinholes?
What do I do to create a smooth surface? I never had this problem when I was using school materials and dipping my glazes, but I can't dip at this point in the game and have very limited resources.
K. Heicksen

#2 neilestrick

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Posted 11 June 2013 - 05:16 PM

Mae sure you're not working the surface with a sponge during throwing/forming. It will remove the fine clay particles and expose the larger rough particles. I always go over my pots with a metal rib to smooth the walls before removing them from the wheel.
Neil Estrick
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neil@neilestrickgallery.com

#3 Diane Puckett

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Posted 11 June 2013 - 06:40 PM

Glaze will not cover a rough surface and make it smooth. It generally just makes any flaws in the clay more obvious. If you want smooth, consider using a clay with less or no grog. Groggy clays can be easier to work with, but, as Neil said, wiping with a sponge just exposes the grog. Wiping with your finger or a damp piece of chamois tends to smooth it. When trimming, you can use a smooth stone or wooden rib to smooth leatherhard clay.

If you can feel the roughness on the finished piece, it is probably from the grog in the clay. Pinholes are tiny holes in the glaze, so the surface feels smooth.
Diane Puckett
Dry Ridge Pottery

#4 Min

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Posted 11 June 2013 - 08:01 PM

The pinholes are probably the result of not enough ventilation of your kiln during bisque firing. If your kiln doesn't have a peephole is it possible for you to add one or two? I think this would help a lot with the pinholes. Pick up a kiln peephole plug(s), disconnect the power to the kiln, turn off the breaker and start with a small size drill bit from the inside of the kiln and in a spot where you have clearance around the elements. Enlarge the hole to the proper size to fit the plug. Obviously be very gentle with the drilling, move up to a small round file when enlarging it. Vacuum kiln thoroughly when done. The hardest part would be cutting through the outer metal case of the kiln. Again, use a small drill bit first, from the inside, then gradually enlarge it. Other option would be to buy a kiln vent but those can be pricey.

Use witness cones also, quite often kiln sitter small cones fire cooler than large witness cones. If you don't have a peephole you are just guessing when the kiln has actually reached the cone you are aiming for. Bisque firing slowly and to ^04 with plugs out until the kiln glows dark red inside will usually take care of most pinhole issues.

If you are having a rough surface even on your burnished pot then perhaps your glaze just isn't applied heavy enough. Try using test tiles from both rolled out clay and thrown clay, brush on 2, 3, 4 coats of glaze, and fire them on a scrap piece in case they run. Make both types of test tiles, if you are exposing sand/grog during your throwing then those test tiles will look different from the rolled ones. Again, it would really help to use witness cones, some glaze can thin out when overfired, if this is happening the sandy texture would also be more apparent.

Good luck, we have all been there!

Min




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