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Note 2 - Inventory - Summary of Inventory (Details) - USD ($)
Mar. 31, 2020
Dec. 31, 2019
Furnace parts and supplies $ 925,300 $ 621,991
Raw materials 1,967,234 2,125,921
Work in process 1,877,131 1,624,499
Finished goods and filtration systems 1,209,729 1,492,135
Reserve for obsolescence (654,895) (665,308)
Net Inventory $ 5,324,499 $ 5,199,238