I would speculate that the flame of your stove ignited the gases that had accumilated on top of and around the container containing the cloth.
I made a device to visually help me determin the correct distance from stove to bottom of pot. It’s adjustable, raises and lowers the pot in relation to the stove top. I was using windshield washer solvent in my glass pot because of freezing temps in my garage(too lazy to get fresh water from house)I didn’t realize there was enough alcohol in the fluid to be concerned about. As the wndsld solvent heated up the alcohol vapors ignited by the stoves flames coming up the side of the pot without me knowing it.
The flames inside the pot being invisible during the testing. I made ready my camera to make a movie of the testing under dark conditions and then shut the lights off. to my surprise, I could then see the flames inside the pot. I took some photos of the flames to be posted with test results on my website bplite.com.
This is why I speculate flames came up along side the container being used to bake the cloth and ignited the gasses coming out the hole.
First two photos are a steel mesh cone shaped wood burner that worked very well.(MYOG)
The second two are of the device used to determine correct distance burner to pot. The burners flame is visible inside the glass pot. The flames changing color and pattern can be seen clearly through the pyrex type glass.
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