Raku firing temp.

[terrim8]

Just about finished building my raku kiln. It is the metal cage type with a base and a top portion that lifts off. The plan came from a book about alternative kilns- its the raku "rocket"!

I would like to buy a nice pyrometer but it will have to wait for awhile. Can i just judge the temp with cones? Visually? 

I will probably do a test firing for glazes with a load of test tiles first.

[Mark C.]

I have only done it Visually-never used cones-you can see the glaze melt or if no t glazed then the color of the glow will tell you the temp.

You can use cones but usually its a many times over deal or with me it used to be -fire feet then in hot/warm kiln do some more.

[JohnnyK]

During my Raku class at Sierra College in Rocklin, CA last fall our prof was pretty insistent on firing the kiln to ^06 using witness cones. We had a pyrometer in place but she felt the cones were more reliable. There were times when we did 2 firings in an evening and a couple of times we were able to do 3 firings. The results were pretty consistent throughout the semester. We made and used test tiles but the were not the best to use as a baseline since each pot and reduction process is inherently different. 

I built my own kiln last spring and so far have only done Horsehair Raku in it and have found that ^017 is a good temp to work with because at higher temps the horsehair tends to burn off before it attaches itself to the pot. These pieces were three done at this temp. Each was fired individually because I found that while I was processing a jar, the others in the kiln would cool too much for effective lay-down of the hair. Refiring the cooled pot would result in very fine hairline cracks in the piece.  These were juried and accepted as a submission for a local PBS TV station (KVIE in Sacramento) for their annual art auction in October.

 

[Gabby]

1 hour ago, JohnnyK said:

During my Raku class at Sierra College in Rocklin, CA last fall our prof was pretty insistent on firing the kiln to ^06 using witness cones. We had a pyrometer in place but she felt the cones were more reliable. There were times when we did 2 firings in an evening and a couple of times we were able to do 3 firings. The results were pretty consistent throughout the semester. We made and used test tiles but the were not the best to use as a baseline since each pot and reduction process is inherently different. 

I built my own kiln last spring and so far have only done Horsehair Raku in it and have found that ^017 is a good temp to work with because at higher temps the horsehair tends to burn off before it attaches itself to the pot. These pieces were three done at this temp. Each was fired individually because I found that while I was processing a jar, the others in the kiln would cool too much for effective lay-down of the hair. Refiring the cooled pot would result in very fine hairline cracks in the piece.  These were juried and accepted as a submission for a local PBS TV station (KVIE in Sacramento) for their annual art auction in October.

 

These are really stunning. I cannot imagine anyone not wanting one of these.

[neilestrick]

No cones needed for raku. The firing is too fast for them to work. Peek in the kiln occasionally, and you'll see the glazes start to bubble up. Once they settle down and go glassy, they're ready to pull. The pyrometer is nice for repeatability, though, so you don't have to keep peeking in the kiln.

For horse hair, you only need to go up to about 1025F. Hotter than that and you greatly increase the risk of pieces cracking as they go through quartz inversion as they cool quickly.

[terrim8]

Those jars are gorgeous Johnny! Thanks everyone- I thought it could be done visually as per all the reading I've been doing but it feels reassuring to check  

[preeta]

Congratulations Johnny.  I’ll be looking forward to seeing your name on the screen and squeal I know him.  

Pyrometers depends on the type of Raku you do. For glaze fire just used visual cues. 

But for mica Raku and horsehair  needed pyrometers. With mica the temperature was important and length of time of reduction otherwise the mica would lose or change its colour. It’s make up grade fine mica.

Dave Hodapp a retired chemistry school teacher does a lot of mica Raku   https://goo.gl/images/jh3q36 

https://goo.gl/images/oxo2Du

[Mark C.]

I call it seat of your pants firing-you learn to read temp by color-its another skill that potters need to learn.

[Benzine]

I do use a pyrometer, but really only for the first part, where I preheat a bit.  At those stages, there isn't much heat color to go by.   However, I do use glaze appearance, to know when it's time to pull them.