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Note 2 - Inventory - Summary of Inventory (Details) - USD ($)
Dec. 31, 2020
Dec. 31, 2019
Furnace parts and supplies $ 471,622 $ 621,991
Raw materials 1,955,713 2,125,921
Work in process 2,394,481 1,624,499
Finished goods and filtration systems 1,424,171 1,492,135
Reserve for excess and obsolescence (723,949) (665,308)
Net Inventory $ 5,522,038 $ 5,199,238