Raku pottery kiln and glazing technique - GIF

Traditional Japanese raku pottery kiln and glazing technique.

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Previously:

https://www.homemadetools.net/forum/...821#post129219
https://www.homemadetools.net/forum/...124#post149575
https://www.homemadetools.net/forum/...814#post140292
https://www.homemadetools.net/forum/...1660#post94342
https://www.homemadetools.net/forum/...779#post140153

Strange that it does not pop when they add the water??

Trigger, I suspect that the reason the water (?) is relatively calm in the brief interval between pouring it into the cup and adding the black substance is a phenomenon that I was told is called calefaction (but which definition I cannot find online today). In my youth (70 years ago) the father of a friend of mine worked in a liquid air company and we were let loose in the company lab after hours to play with some liquid nitrogen while waiting for a ride home. We asked why a drop of liquid nitrogen would gently skitter around on a metal plate for many seconds without losing any apparent volume, then suddenly disappear. We were told it was due to calefaction, the creation of a thin film of N2 gas formed between the plate and the drop that insulated the drop from the hot (relative to the temp of LN2) plate until the gas film was disrupted and the drop would boil away in an instant.

Same phenomenon occurring between the red hot cup and the water? Then, when he drops the black substance into the cup it disrupts the steam film and the fluid suddenly boils away explosively.