In my experience, the thermocouple will age. And as it ages, if it is hanging out in the air (not tubed), it will start dropping little bits of ashy metal flakes. They may be small to begin with and you might not notice right away.
To check your thermocouple, just
1. (IMPORTANT) Unplug your kiln
2. Set A white shelf under the thermocouple
3. LIGHTLY scratch over the thermocouple metal part with your fingernail. (Do not apply pressure.)
Check to see what drops onto the shelf. If you had a pottery piece that was getting glazed, that’s the junk that ‘s going to land onto your glazed piece.
If your thermocouple is new enough and the ash pieces are small enough, you may not have noticed yet, but sooner or later, without protection, you will likely find a ruined piece in your firing.
My kiln uses an environvent.
Pottery tip for preventing ashy metal flakes on your electric kiln glazed ware:
Throw a short cylinder, vertally cut off about a third , and fire it under the thermocouple. The black ashy type substance falls into the cup bottom instead of on your wares.
Just leave enough room for the thermocouple to work when stacking your shelves and you will keep a nice clean kiln.
I’ve been using the same cylinder for a couple of years. See how black the bottom is!
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