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Note 2 - Inventory (Tables)
 12 Months Ended
Dec. 31, 2019
Notes Tables  
Schedule of Inventory, Current [Table Text Block]
   
2019
    
2018
  
Furnace parts and supplies
   $
621,991
     $
596,806
  
Raw materials
    
2,125,921
      
1,659,826
  
Work in process
    
1,624,499
      
1,691,175
  
Finished goods and filtration systems
    
1,492,135
      
1,596,042
  
Reserve for excess and obsolescence
    
(665,308
)
    
(1,111,794
)
Net Inventory
   $
5,199,238
     $
4,432,055