Temperature Conversion Cones to Bars

[Pagan Clay]

Hi y’all!  Beginner ceramist here!  I have some over glaze decals and lusters I want to try, but I’m in a community studio that won’t fire that low (come 018-019). I have however found a friend at the studio with a personal kiln willing to fire this low. However she uses bars instead of cones. How can I convert the cones to bars so that she knows how to fire them?  Is there even a way to do this?  Here’s the decal for reference- https://www.chinaclayart.com/collections/overglazedecal/products/gold-bee

 

Thanks in advance for your time, help, and input!

[Dick White]

The mini-cones and pyrometric bars are more-or-less equivalent. Some would argue that the bars are more accurate, in that they cannot be shifted to one end or the other to slightly change the outcome, but if her bars are 018 or 019, they will be fine for your work.

[PeterH]

Looking at the table Orton Cone Chart I'm surprised/confused that the  heating rate assumed for small cones is so much faster than for regular ones.
https://www.ortonceramic.com/_files/ugd/7c9d79_11dd303c800c46b08d3a05178a02d99c.pdf
Small at 300°C/hr and regular at  15°C/hr, 60°C/hr & 150°C/hr.

Is there a simple explanation?

I note that a footnote states the small cones were fired in a gas kiln, while bars are typically used in a electric kilnsitter.

 

Edited December 2, 2023 by PeterH

[High Bridge Pottery]

The blurb on the right says  (incorrect information - see Hulk's next post)

Quote

Temperatures shown for small cones were determined using a heating rate of 300C/hr (540F/hr) in a gas fired kiln. Small cones will come close to duplicating the results of self-supporting cones if mounted upright, properly simulating the position of a self-supporting cone. Typically, small cones will deform 7-10 degrees C earlier than a self-supporting cone, so the temperature values for a self-supporting cone can be used to determine an equivalent small cone temperature by subtracting 7-10 degrees C (or 12-18 degrees F).

 

Edited December 3, 2023 by High Bridge Pottery

[Hulk]

There had been discrepancies in Orton's online materials regarding small cone deformation temperatures*.

I used small cones for the kiln sitter (prior kiln), and I like them. They are a tiny bit cheaper.

Here's an excerpt from the message I received from Orton Engineer (circa March 2020):

Dear Sir,

 

Thank you for contacting Orton to draw our attention to some incorrect information on our website.  The small cones do in fact deform after the large cones.  We have updated the information on the website. 

 

See also this thread (start at the bottom/end) Kiln Sitter cone for witness cone - Studio Operations and Making Work - Ceramic Arts Daily Community

 

*There still are! The 2016 cone charts are all "backward"

 

See the small cone page, SMALL CONES | Orton Ceramic
"Small Cones used on the kiln shelf deform at about 9°F after Large or Self-Supporting Cones of the same number."

It's just because the small ones are smaller - the cones are same material; same reason a large candle will slump in hot weather before a small one.
 

[Callie Beller Diesel]

I was told that another part of the reason for the small cones deforming later is that they have the weight from the kiln sitter arm applied to them, where self supporting and regular cones don’t. So the later melt is to help compensate for that, as they’re being used as a shutoff.