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Note 2 - Inventory - Summary of Inventory (Details) - USD ($)
Jun. 30, 2021
Dec. 31, 2020
Furnace parts and supplies $ 417,608 $ 471,622
Raw materials 2,581,670 1,955,713
Work in process 2,004,560 2,394,481
Finished goods and filtration systems 1,193,052 1,424,171
Reserve for obsolescence (622,403) (723,949)
Net Inventory $ 5,574,487 $ 5,522,038