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Note 2 - Inventory (Tables)
12 Months Ended
Dec. 31, 2020
Notes Tables  
Schedule of Inventory, Current [Table Text Block]
  

2020

  

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