Briefly, your quality specification should mention : 

1. the admitted defects and their admission proportion 
2. that no other defects than the above indicated are admitted 
 

Putna is an export quality specification :

A. Natural Defects

1.Knots
Category a and b partially intergrown admitted on faces and edges without affecting the timber piece resistence 

On faces : 
b dead and c :up to diameter 25 mm - unlimited admitted 
up to diameter 30 mm admitted 1 piece/meter 

On lateral sides : 
category b dead (falling) and c 20 mm and up admitted 2
pieces/edge; also admitted 2 pieces with diameter max. 25 mm unthrough. 

2. Cracks 
Unthrough straight cracks : admitted on faces and edges
cumulated 2/3 from piece' s length without being largely opened 
Through cracks : on face is admitted 1/3 of piece length; on heads admitted cumulated on 2 times timber piece length. 

3.Insect Holes 
Admitted small and medium sized without larves and alive
insects. 

4.Red and blue stains 
Admitted on both faces and edges cumulated on 1/2 from piece's surface. 

5.Mould 
Dried and superficially - admitted on stains form up to 20% of piece' s surface. 

6.Hard sap rot 
Admitted on a face and a lateral side 1/4 from length and width.

7.Soft Sap Rot 
Admitted on points form which cumulated cannot surpass 4 cm³, without appearing on edges and heads. 

8.Obtuz Wane 
Admitted on an edge  1/4 from length and on face 1/3 from thickness well cleaned of bark. 
 

B. Preservation and Processing Defects

9.Cup 
Admitted with arrow of max. 4 mm. 

10.Spring, simple bow and twist 
Admitted with arrow of max. 0,3% of length. 

11.Snakings 
Admitted sligth form at max. 15% of quantity. 

12.Thickness deviations 
Admitted at +/- 1 mm. 
 

C. Other Defects

13.Not admitted.

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a category knot - healthy, intergrown 
b category knot - healthy, partially intergrown, dead or falling 
c category knot - unsound and rotten knots