Cold Zone under kiln shelf?

[Jenna]

I currently have my cordelite shelf on 2" kiln posts with a 1" gap between the shelf and the kiln wall.
The bottom elements begin just over the top of the shelf.
The top elements are 9" from the shelf surface.

My problem...
I do mostly frit casting in open face refractory molds and have been having more and more pieces come out where the glass hasn't melted into the base of the mold and filled in the detail of the mold.
I have had this same setup for years and have had reasonable success, however I'm recently getting more and more scrap pieces.
25-30% scrap vs about 5%
This has been baffling since I'm also using a kiln schedule that has worked very well for thousands of castings.

My question...
Would it make sense to raise the kiln shelf another 2" to try and get some heat under the shelf? Will this even get heat There without some kind of ventilation to draw the heat there?
Or adjust my schedule and Heat longer/slower during the firing?
My current thinking is That the glass is presssing into a cooler base, which is the last place to "see" the heat and therefore not forming well.

I ordered an external thermocouple to measure the temp down there but it won't arrive for a few days.

Your thoughts and insights would be much appreciated.
Where do you position your shelves?

[Brad Walker]

Get rid of the shelf. Just use posts.

Also, I'd hold a little bit longer at your top temperature than you have been.