hold cycle

[Bonnie Hornsby]

Is it that important to add a hold to your firing cycle?  Does it make that much different to the end result?  Any feedback would be much appreciated. 

Bonnie Hornsby

[Norm Stuart]

The purpose of a short hold, on the order of ten minutes, is to equalize the temperature in different parts of the kiln. There are also some glazes which become chemically reactive or off-gas near the peak temperature. Holding for as long as twenty minutes can allow these glazes to lay down after the reaction or bubbles have left the melt, leaving a smooth surface during the cooling process.

Some have reported longer holds resulted in more pin-holing. Personally I've never seen this. All reactions stop at some point.

Longer holds at a particular temperature can be used to favor formation of certain types of crystals or chemistry, such as with macrocrystalline glazes.

Adding a controlled slow-cooling after your firing will provide different results, often radically different. Slowing the rate of cooling between approximately 1,800 F and 1,500 F to 180 degrees F per hour, or even slower like 50 degrees F per hour, will closely emulate the glaze formation process in a hard-brick gas kiln which naturally cools more slowly than the foam core brick used in electric kilns.

Try different approaches and discover something new.

[john autry]

Hmmmm. How do you hold if you have a manual kiln with a kiln sitter? Are some glazes only meant for programmable kilns? I hope not.   

[George Lewter]

John,

See the article at http://cone6pots.ning.com/page/how-to-downfire-a-manual-kiln for how to do holds and controlled cooling on a manual kiln.

[john autry]

john autry said: Thanks for the information , George. I'll check it out. ja

[Bonnie Hornsby]

Thanks so much, Norm.  This information is so beneficial.

[john autry]

Yes, this information is useful and appreciated. Thanks Norm. ja

[Norm Stuart]

Once you find yourself frequently baby-sitting your kiln-sitter at the end of each firing, to perform holds and slow-cools, the $500 cost of replacing your kiln-sitter with a computerized kiln controller will soon seem like the most sensible investment you have ever made.

Another valuable contribution of a computerized controller is the ability to perform multiple hour pre-heats on greenware and and freshly glazed pieces which are not completely dry. Using a nail in place of a bar cone while you turn the kiln on and off, to keep the temperature just below 200 F, is not quite the same as setting it and walking away.

At some point $500 divided by all your time turns out to be far less per hour than you'd earn working in a sweatshop in a third world nation.

john autry said:

Hmmmm. How do you hold if you have a manual kiln with a kiln sitter? Are some glazes only meant for programmable kilns? I hope not.   

[Jeff Poulter]

You can get some plug & play controllers off of e-bay for less than $500.00.  You have to size your kiln with the appropriate controller on the amperage.  You plug the controller where your kiln was plugged in, then plug your kiln into the controller, turn the switches to high & program away.  I think they are mostly Orton controllers.  A while back, I even bought a couple of L&L controllers for less than $50/each.  One was a re-build and the other was a demo.  They must have belonged to a sales rep or something.  The one came with it's own wall wart so they could demo it anywhere they went.  jhp

[George Lewter]

We have an existing discussion about retrofitting manual kilns with programmable controllers

[Robert Coyle]

I have not been doing holds at the top end of my firing cycle since I was only using a kiln sitter for a long time. I developed the glazes to work with the sitter. I have gone to a programmed ramp but have not tried a hold except around 200F and 1150F.

The question is would there be a difference between a hold right before maximum temp and the same hold at the same temp after. I assume the glaze is still in a molten state either way. 

[Norm Stuart]

If you're trying to equalize temperature in a bisque, or give glaze enough time to react, a hold could be just as effective before reaching maximum temperature as after. But it's different for us.

We use our Bartlett controller's pre-programmed cone fire, so all holds occur after the cone fire is completed. We still choose a cone-fire program one cone cooler than we want, as even with a new Type-S thermocouple, our kiln still reliably fires to exactly one cone hotter, by witness cones, than it's programmed for - when fired without a hold or slow-cool. I'll take reliability any day, even if it occurs in a round-about manner.

Slow-cools obviously need to occur after the peak temperature in either case. And unless you happen to be sleeping next to your kiln, witness cones don't mean much when you're adding on slow-cools.  Additional heat work may be done during the slow-cool, but that's not why you're slowing down the cooling cycle. You're accumulating glaze crystallization.