old thermocouples lose integrity as they age and it maybe the T?C is wore out and not reading the proper temp. if this is the case you need to change the t/c. several things could give this result, t/c and or elements
no need for 3 phase, just get another 11 cu ft, better return on investment. When you mentioned hand building, are you slabbing the clay , cutting out a template, and wrapping it around a form, then attaching a bottom then handle? If so, where is your bottleneck.
To give you an idea of labor cost, a contract potter in Seagrove, NC, who turns for several potters during the week, works at about $1.25 to $!.50/lb of clay. The clay is weighted and ready for him to turn, no handles,no trimming, just turning.
As suggested above rolling the bottoms save time
Since these contract potters work by the pound, they must produce enough to prosper, a hundred lbs a day is common.
At 3lb of clay labor and clay equal to $6/piece +/-.
Clay can be thrown and covered so your production can exceed your daily demands as well, store in damp box..
If your hand builders are making just the tile badges that are applied, these too can be stored by wrapping and storing in a damp box.
If you don't have an extruder, get one for handles, you can make the die out of 1/4 in lexan and cut the handle pattern out with a drill press and a jig saw. Extrude the handles and form them on a board to firm up. There again keep in a damp box till ready to apply.
You can make 200 handles in an hr if needed.
Next get a larger kiln to add to what you have. If you have the power to handle the amps and the margin to handle the expense.
Just a few thoughts, hope some help, no idea if these fit your situation.
Add water seal and let sit for a day or 2 then start stir until things start loosening up . You might want to invest in a kitchen stick blender for about $10 or so to help blend these back to a usable consistency. You'll need to screen the glazes and some may have hardened lumps from some ingredients crystallizing.
Put those aside in a bowl after screening and try dissolving them in a small amt of hot water, after dissolving, add this back to the glaze.
Test these glazes on some test tiles by themselves as well as in concert with out glazes you might be using. This will allow you to make a palette to refer back to.
I've had glazes dried out for years that I forgot about.They are as good today as when I made them, just some work to get them back to the right consistency