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Note 2 - Inventory (Tables)
 6 Months Ended
Jun. 30, 2019
Notes Tables  
Schedule of Inventory, Current [Table Text Block]
   
201
9
    
201
8
  
Furnace parts and supplies
   $
730,370
     $
596,806
  
Raw materials
    
1,756,414
      
1,659,826
  
Work in process
    
1,501,307
      
1,691,175
  
Finished goods and filtration systems
    
1,527,554
      
1,596,042
  
Reserve for obsolescence
    
(801,990
)
    
(1,111,794
)
Net Inventory
   $
4,713,656
     $
4,432,055