Help With Older Cress Kiln

[MarkS]

I am looking for some help with a older Cress kiln. It is a model FX-27P with the Kiln Sitter and Firemate Speed Control. As I understand it the speed control determines what percentage of total power is going to the elements over time. At the slowest speed it ramps up about 10%/75 minutes, at med. slow its 10%/45 min. and so on. The manual says to start at "0" and use a slow speed for bisque firing hand turned ware. It really doesn't go into much more detail. I did a ^6 glaze firing this weekend at med-slow speed and it took about 11+ hours.

So I'm looking for some practical advice as to how I need to be using the settings for best results - either from personal experience or just ideas.

Thanks!

[Idaho Potter]

I've been using a Cress FX-27P with a Kiln Sitter for 25 years. The only time I ever use slow speed is when I have sculpture pieces and want to make sure they are truly dry before firing bisque. Sometimes the clay thickness isn't as even as I'd like so I lean towards the safe side. If you are throwing pots and know they are dry you can start at fast speed, although I usually use medium.

 

My instruction manual says to start at the number one, leave the lid propped open for the first hour or so, ALWAYS leave the top peekhole open throughout the firing. That's pretty much what I do. Since I got a digital Skutt, I mostly use it now for firing bisque (cone 06 to 04), but when I have a lot of glaze work it takes the overflow and fires to cone 5 - 6 without a problem.

 

Bisque firing takes from 4.5 hrs to 6 hrs. Glaze firing takes 8.5 to 12. Time depends on how heavy the load is and firing speed. Until you get used to the kiln's idiosyncrasies, I'd err on the side of caution. Better to use slow speed that might take more time than to lose your pots. Keep a ledger to refer to (i.e., size of load; type of work fired; firing speed; time elapsed). I'd also suggest setting the hour timer to at least one hour more than you think is needed (on glaze firings I set it for two extra hours).

 

Hope this helps. If you bought this used, check the elements and cone assembly for wear--this should give you good service for years to come.

[MarkS]

Thanks for the help. I've basically been doing as the manual says but was interested in more practical experience. I wondered if you need to change the speed as it got hotter or just let it do its thing.

It appears to be little used and in pretty good shape. And the price was right!

I've wondered about the logic of leaving the top peephole open. I was told for oxygen? But I've heard of others who never take the plugs out.

A pyrometer isn't the budget right now.

[Idaho Potter]

I leave the top plug out always, but I don't know if it's habit or a compelling reason. One reason is to give an exit for any stuff burning off the clay or glazes. It might take a bit longer to fire a load, but not much. I tried changing the speed halfway through a glaze firing and it was not a good result. I thought if I turned the speed down it would work like a soak. Hah! Not so much.

 

As to pyrometers--I've not had much luck with mine. Even doing raku, I have better luck eyeballing the pieces than depending on pyrometer reading. I'm sure this is operator error.

 

I suggest you load the kiln, place sight cones (even if you only use them to verify the kiln fired to proper cone), put the junior cone in the kiln sitter pick your speed, time, and press the button to start. Afterthe first hour close the lid and pray. That's how I do it.

[MarkS]

Thanks for the help!