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Note 2 - Inventory (Tables)
6 Months Ended
Jun. 30, 2021
Notes Tables  
Schedule of Inventory, Current [Table Text Block]
   

June 30,

2021

   

December 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