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Saturday, April 17, 2010

Pinholes, yep, but......read this

Wesley's band played at Clydefest today so we spent the day out with her and I didn't get a chance to photograph the kiln I unloaded at 7am this morning. I'll do it tomorrow because I have some nice things to show you. I worked on a very large house box yesterday that I am really excited about, although the roof part got too dry over night, guess I didn't wrap it as well as I thought and I broke it to bits today in a small fit I had. Oh well, I'll make another one.
In other news, yep I had lots of pinholes, I don't care, the forms are nice and the glazes are great so I am going to live with them and just tell people it costs extra to put in the pinholes! But the best part is I had a lightbulb moment after I unloaded and tried for the life of me to figure out what I was doing wrong. I have tried everything, my bisque is getting to be about 14 hours, lord! I soak the bisque at 1100 f, I sand the pots, wash the pots, the glaze was a commercial glaze, I soak the glaze fire near the end, used different clay bodies, blah blah blah...... and then I read this on digitalfire:
A very important factor to consider also is that modern industrial kilns supply a lot of airflow to the chamber and this carries away products of decomposition. If you are using a kiln without adequate ventilation then there may be not be enough oxygen available at the glaze surface to oxidize and carry away the carbon products of decomposition. Ventilation systems can be added to kilns but that does not mean they are adequate, the air may not be passing over all sections of the ware or at a great enough rate. Some industrial kilns have so much airflow that taller ware can actually blow over if it is not set correctly! If you are doing fast-fire this is critical, a fast fire kiln absolutely must have good air flow. If you are using an electric kiln without airflow, then expect glaze imperfections unless you are firing very slowly.

and that is when I realized there was one more thing that might be causing the problem. When I first got this kiln I had no pinholes at all. Then I went to a friend's house to see how they fired a reduction with the same kiln and I came home and cranked down the burner ports to 1/4 inch to allow for LESS OXYGEN! TADA, could this be my problem? Do you think that there is less ventilation going through the kiln? It seems that way to me, soooo, next firing I am opening those ports back to the way I had them and see if that does it, if not, I will be the famous pinhole potter haha!!!!

6 comments:

amy said...

Glad you figured that out!

Just as another possibility: I have a friend who was having problems with pinholing and blistering. She was told to soak her bisque for a half an hour at 1500 degrees to insure burning off all organic matter and then continue to cone 06. This has solved her issues. I haven't tracked along the entire way with your glaze issues, so sorry if this is a repeat suggestion!

Tracey Broome said...

I soak the bisque for an hour at 1100, can't remember who told me to do that but I read in the Ceramic Spectrum about what was going on at 1100 and it made sense. I fired to 04 this time, seemed way hot but I'm willing to try any and everything at this point! Just think how smart I'm going to be one of these days :)

Tracey Broome said...

Oh by the way, Amy, I am enjoying the baby blog!! Can't believe how fast those two are growing!

Dirt-Kicker Pottery said...

I got a noticable improvement when I installed my kiln vent/fan. I still get a pinhole here and there, but nothing like a few months ago.

ang said...

wow ... excellent that you've back tracked to the changes you made... i really hope this solves it coz i think you have it covered now..thanks for dropping in on my glaze unload i was having some doubtful moments yesterday on the shinos and i'm going to blame it on the baby quake we had friday night. peeps have been acting weird!! it was only a 3.8 and totally strange the way it affects folks..

cookingwithgas said...

worth a try isn't it!
Hope you make it over to join us!