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Note 2 - Inventory (Tables)
6 Months Ended
Jun. 30, 2020
Notes Tables  
Schedule of Inventory, Current [Table Text Block]
  

June 30,

2020

  

December 31,

2019

 

Furnace parts and supplies

 $834,710  $621,991 

Raw materials

  1,980,305   2,125,921 

Work in process

  2,124,366   1,624,499 

Finished goods and filtration systems

  1,084,111   1,492,135 

Reserve for obsolescence

  (666,878

)

  (665,308

)

Net Inventory

 $5,356,614  $5,199,238