I recently purchased a used RioGrand kiln and would like to use witness cones near my piece to confirm it's getting to temperature. My wife uses them in her pottery kiln and wondering if I would use similar style cones for getting a tool to 1575 fahrenheit and holding for 1/2 hr.

I'm sure the temperatures will be different depending on how high or how close to the wall my piece is. That's why I want to test several areas inside the kiln.

Anyone have any experience with them?

Dave Hake 

Ft. Collins CO 

Are they available in the temperature ranges you want? If so I can't think of a reason they won't work for determining forge temperature accurately.

I don't know pottery so my opinion is worth what you paid me.

Frosty The Lucky.

Well, I haven't used cones in close to 50 years, so take this for what it is worth:

1. Ceramic cones are a temperature over time system.  My feeling is that it will likely be helpful to get a better picture of the variation of temperatures in your kiln in different locations, but not necessarily a good indication of the actual temperature within a couple of degrees that you would get with use of a proper thermocouple.  By all means put a bunch of cones of different ratings on shelves in different locations in your kiln, but I would take that as a relative test rather than an exact indication of what temperature each location is holding.
2. If you are using the kiln for heat treatment, the controller and associated sensor are really the critical piece of kit you need to setup.  The cones may tell you what peak temperature the kiln gets to, but a calibrated thermocouple and readout will give you an instantaneous reading.  Control systems are prone to drift, overshoot and hysteresis.  Any of these can mess with your planned heat treatment cycle.  Fortunately most simple carbon steel heat treatment doesn't need +/- 10 degree accuracy to give an acceptable outcome.  Still, proper selection and setup of a correct controller/sensor system will lead to success more often than not.
3. Your high power (coil supply) switch is also critical to good heat treat oven performance.  Old school standard contactors will eventually arc, oxidize and fuse.  SCR are great, but can be expensive and hard to tune.  I used to use mercury relays in my builds.  They are a good compromise between contactors and SCR, particularly if you can source them cheaply from a liquidator like I did. 
4. All things being equal, the more thermal mass in the system the slower, but more stable the heating.  

Thanks Latticino,

I figured the cones were related to time as well as heat. That's why I wanted to see if there's a formula for picking the right ones. I'll experiment with a few and at multiple levels.

The kiln is programmable with display and an "Even heat" lining, so it 'should' be fairly even, but I tried to anneal a farriers rasp in it and it didn't turn out as annealed as the same brand that I heated up in a forge and stuck it in vermiculite. That's why I wanted to do some testing.

Looks like a nice, solid piece of kit.  With the controller properly tuned (and if the coils are still good) it should easily be able to accomplish what you need.  Note that it does appear to have some significant thermal mass, which is a double edged sword.  As noted, it should keep temperatures more stable, but it will also take more time and energy to get up to heat.  This will also impact you being able to easily double purpose it as an austentizing oven and a tempering one.  A cheap toaster oven can also be used for this (they can also be fairly easily modified to perform really well at this).