Great shape and look to this soda fire flask. Fired on its side in the kiln and lined with a deep amber glaze. (cork not pictured)
Basically we fire a gas kiln to 2350 degrees. The kiln has "soda" introduced to in the last hour to help effect the bare outside of the usually unglazed pots. There are many ways to accomplish adding this soda and many recipes for the soda itself. We added a sodium carbonate mixture to boiling water and sprayed it into the kiln then allowed the kiln to re-heat and get to temperature before shutting it down.
Functional flask. Food, dishwasher and microwave safe